Climate change

Six notable extreme rainfall events have occurred within the past thirteen years in the GTHA, resulting in damages due to flooding. This figure shows a notable extreme rainfall “near-miss” event, labelled “Lake Ontario 2012”.

Radar tracking of the August 10, 2012 extreme rainfall event. The Lake Ontario nearshore experienced sustained intensities approaching 200 mm/hr, while the southern portion of Peel Region had no measurable precipitation. (Source: Risk Sciences International)

Drought conditions at Island Lake in the summer of 2007

Climate-related impacts

Since 1995, Ontario has had a weather-related state of emergency almost every single year . The City of Windsor saw extreme events that caused severe flooding in 2007, 2010, 2016 and 2017 . The Ottawa region experienced one extreme event every year for five years, and in the Greater Toronto Area (GTA), there have been four extreme rainfall events in the past ten years . Such high intensity events produce heavy rainfall in relatively short periods of time. While it is reasonable to expect runoff to be produced under such conditions – particularly when rain falls which exceeds a soil’s hydraulic conductivity - the production of stormwater is exacerbated in urban areas where the overwhelming majority of surfaces are impervious. The problems associated with managing stormwater volumes are exacerbated when dense stormsewer networks efficiently convey stormwater runoff volumes from a large contributing upland area to a single outlet location, such as a stormsewer outfall in a river or stream.

In July 2013, the GTA experienced its most severe storm event in 60 years. Nearly five inches (126 mm) of rain fell in a two-hour period. In comparison, during Hurricane Hazel (a devastating event in 1954 where 81 lives were lost), the two-hour maximum precipitation was 91 mm and the total amount of rainfall was 285 mm over nearly two days . Conventional municipal drainage systems could not carry stormwater away fast enough. Roads and highways were overcome with floodwater closing major transportation corridors including Highway 427. GO Train passengers were stranded, and power outages and basement flooding were widespread with property damage of more than $1 billion .

While it is nearly impossible to ascribe the cause of a single event to the broader issue of climate change, the trend is clear: an increasing number of high-intensity, short-duration (HISD) events are impacting our urban areas, exacerbating the stresses on overtaxed stormwater infrastructure. The figure highlights a series of seven recent extreme rainfall events which have struck the Greater Toronto and Hamilton Area (GTHA). On August 10, 2012, a large storm tracked across Lake Ontario parallel to the Canadian shoreline. Situated only 15 km southeast of Mississauga, this event lasted 6.5 hours and had estimated sustained intensities of 150-200 mm/h (see Figure). While the impacts of extreme rainfall events on urban areas cannot be ignored, the increasingly prolonged, dry inter-event periods necessitate that stormwater infiltration and percolation be maximized in order sustain base flows in support of aquatic ecosystems.

While urban flooding and extreme rainfall garner the most attention in discussions pertaining to stormwater management, it is crucial that consideration also be given to the management of our water cycle during dry periods as well. Collectively, we need to be able to manage extreme rainfall events such as the July 8, 2013 storm, combined rain and snow events such as that which caused the Bow River flood in Calgary in 2013, and extended periods of drought as occurred in southern Ontario in 2007. Drought preparedness is required if we are to sustain riverine baseflows, ensure the security of drinking water resources and optimize both water and waste water infrastructure.

As municipalities grapple with these new climate realities and their associated costs, they are rethinking how to manage stormwater using a variety of innovative solutions. The figure illustrates what has already happened in Ontario under conditions of prolonged drought. The Island Lake Reservoir, located near the Town of Orangeville, saw significant drawdown during the summer of 2007 after a period of prolonged drought. Reliant on groundwater for its municipal supply, continued pumping by the Town led to a significant drawdown within the reservoir. This was problematic not just for the ecosystem of the Lake, but for the downstream wastewater treatment plan as well, which relies on discharges from the reservoir in order to ensure that treated effluent can safely be assimilated by the receiving watercourse.

Concerns with projections

• Even if we significantly reduce GHGs, the impacts of climate change will continue
• There is uncertainty in the models, confusing policy makers and practitioners
• “The extent of the impact of climate change is not fully known, and there are limitations in understanding the Earth’s climatic variations over long spans of time (CSIRO 2007). Additionally the modelling of climate projections to a local level is still not yet precise. As expressed by the MOE (2011): “Climate change science and modeling currently is not at a level of detail suitable for stormwater management where knowledge of the intensity, duration, frequency of storms and their locations and timing is required. However the economic, health and environmental risks dictate a need to be proactive in the management of stormwater.” These uncertainties require a process for continuously assessing the adapted measures, as well as assessing the physical facilities or infrastructures affected by these adaptations.” Upadhyaya et al 2014
• Climate change should be considered in future planning but the uncertainty in estimates makes it harder for those involved
• “How to adapt cities to climate change is emerging as one of the greatest challenges that spatial planners will face in the 21st Century (Measham et al., 2011; Perry, 2015).” cited in Matthews et al 2015

Climate Trends in Ontario

Observed to date

• IDF: Changing rainfall intensities affect stormwater runoff timing, peak rates and volumes; Methods have been relying on static IDF curves
• Increased frequency of 12% and increase intensity of 16% of extreme precipitation events for 1958 - 2007 for the US Northeastern region (Larson et al 2011)
• “Percent changes in the amount of precipitation falling in very heavy events (the heaviest 1 %) from 1958 to 2012 for each region. There is a clear national trend toward a greater amount of precipitation being concentrated in very heavy events, particularly in the Northeast US (71 %) and Midwest US (37 %). (Figure source: updated from Karl et al. 2009c )”  Melillo et al 2014
• “As for the temporal trends, significant warming trends are detected throughout the province of ON and the overall trend in annual mean temperature varies largely between 0.01 and 0.02 ∘C year–1. Increasing trends in annual rainfall (by 1 – 3 mm/year) and total precipitation (by 1 – 4 mm/year) are detected at the vast majority of gauged stations, but no significant trends in annual snowfall are identified at most of the stations.”  in Wang et al 2015 (Meteorological Applications Journal)
• “Extreme downpours are now happening 30 percent more often nationwide than in 1948. In other words, large rain or snowstorms that happened once every 12 months, on average, in the middle of the 20th century now happen every nine months. Moreover, the largest annual storms now produce 10 percent more precipitation, on average.”  Madsen et al 2012 a study in the US
• “Extreme weather events including prolonged heat waves, torrential rainstorms, windstorms, and drought have increased throughout Ontario in recent years (Ontario, 2011). The frequency of very hot days (above 32°C) is expected to increase by 2.4-fold in Ontario by the late 21st century (Vavrus and Dorn 2009)”.  cited in Thunder Bay, 2015
• “Increases in the frequency and magnitude of extreme rainfall events have been documented in New York State (Fig. 1). These changes are among the largest seen within the United States (DeGaetano 2009). Climate change projections suggest that these increases will continue (Frumhoff et al. 2007).”  in Tryhorn 2010

Projected

• Increase in frequency and intensity of extreme precipitation events between now and 2100 (Larson et al 2011)
• “The analysis indicates that there is likely to be an obvious warming trend with time over the entire province. The increase in average temperature is likely to be varying within [2.6, 2.7]8C in the 2030s, [4.0, 4.7]8C in the 2050s, and [5.9, 7.4]8C in the 2080s. Likewise, the annual total precipitation is projected to increase by [4.5, 7.1]% in the 2030s, [4.6, 10.2]% in the 2050s, and [3.2, 17.5]% in the 2080s. Furthermore, projections of rainfall intensity–duration–frequency (IDF) curves are developed to help understand the effects of global warming on extreme precipitation events. The results suggest that there is likely to be an overall increase in the intensity of rainfall storms. Finally, a data portal named Ontario Climate Change Data Portal (CCDP) is developed to ensure decision-makers and impact researchers have easy and intuitive access to the refined regional climate change scenarios.”  in Wang et al 2015
• “Some researchers, however, have demonstrated that the volume (Kuchenbecker et al. 2010, in Germany; cited in Bendel et al. 2013), frequency (Bendel et al. 2013, in Germany; Fortier and Mailhot 2014, May and October in Canada) or mean annual duration (Fortier and Mailhot 2014,in Canada) of CSOs should increase in the future climate. Logically, these increases will cause water quality to deteriorate in urban rivers – impacts that could be more severe as a result of increased water temperature.”  St-Hilaire et al 2016
  • For York Region: “• Of all temperature variables, the minima are anticipated to increase the most significantly by the 2050s in all seasons and on an annual basis (i.e. minimum temperature, average minimum temperatures) • Precipitation is expected to increase annually and over most months; however, may in fact remain relatively consistent or decrease compared with the current climate for the summer season • Extreme events are anticipated to become more frequent and more extreme. • Extreme heat indicators demonstrate that the number of days by the 2050s experiencing extreme temperatures will increase significantly. On the other hand extreme cold events are anticipated to decrease correspondingly by the 2050s, where the number of days exhibiting extremely cold temperatures could decrease • Extreme precipitation events are likely to increase in magnitude and in frequency, particularly in the summer time when convective activity is highest in and surrounding York Region. The future trend of extreme precipitation intensity; however, is unclear. It is recommended that a conservative approach should be taken in planning and adapting for extreme precipitation events. • The growing season in York Region is expected to lengthen by over 30 days by the 2050s. With this, the start date will shift earlier and the end date will shift later in the year. It is less certain, but more likely than not, that drier conditions will be present throughout the growing season in the 2050s as a result of no significant increase in precipitation over summer months and significant increases in temperatures.”  OCC et al, 2016
• “If [winter] precipitation falls as rain instead of snow, which may actually occur more frequently in temper- ate regions with climate change, phosphorus concentrations in winter have the potential to be equivalent to those observed in other seasons due to the ubiquitous impacts of runoff events.”  Long et al 2014, a study done in Hamilton, ON
• “Another potential impact of climate change on summer nutrient conditions that has been discussed in the literature is an increase of summer soluble reactive phosphorus (SRP) concentrations in creeks during low flow conditions due to temperature-dependent release from riverine sediments.”  Long et al 2014
• “Dominguez et al. (2012) found increases in the intensity of 20- and 50-year return period winter precip- itation events over the western United States, while over Canada, Mailhot et al. (2012) showed that the intensity of annual maxima precipitation would increase, with the largest increases for Ontario, the Prairies and Southern Quebec.”  from Guinard et al 2015
• “The hydrological response to climate change was investigated through stormwater runoff volume and peak flow, while the water quality responses were investigated through the event mean value (EMV) of five parameters: turbidity, conductivity, water temperature, dissolved oxygen (DO) and pH. First flush (FF) effects were also noted. Under future climate scenarios, the EMVs of turbidity increased in all storms except for three events of short duration. The EMVs of conductivity were found to decline in small and frequent storms (return period <5 years); but conductivity EMVs were observed to increase in intensive events (return period ½5 years). In general, an increasing EMV was observed for water temperature, whereas a decreasing trend was found for DO EMV. No clear trend was found in the EMV of pH. In addition, projected future climate scenarios do not produce a stronger FF effect on dissolved solids and suspended solids compared to that produced by the current climate scenario.”  He et al 2011
• “The potential consequences of climate change for P cycling in streams include (i) increasing prevalence of droughts and extreme summer low flows causing a reduction in baseflow dilution capacity, increased P retention during summer as residence times increase and a greater frequency of anoxia (Caruso, 2002; Van Vliet and Zwolsman, 2008), (ii) changes in magnitude and frequency of extreme high flows and floods causing reduced river P retention capacity and net in-channel loss of P under eutrophic conditions, greater seasonal variability in runoff volumes, carbon and nutrient inputs from terrestrial sources (e.g. more winter runoff and less summer runoff), scouring of streams and more frequent flushing of storm sewer overflows (Newson and Lewin, 1991; Schindler, 1997; Biggs et al., 2000; Bouraoui et al., 2002; Wilby et al., 2006a), (iii) greater range and higher average air tempera- tures causing warming of water temperatures in shallow streams, increasing the time window of biological activity, higher rates of primary production, increased soil wetting/ drying cycles, greater rates of OM mineralization and greater dissolved organic carbon (DOC) concentrations reaching the stream with impacts on microbial populations and metabolic rates (Wilby et al., 2006b; Durance and Ormerod, 2007; Harrison et al., 2008).”  Withers and Jarvie 2008 – study on phosphorus in rivers, this quote shows how climate change would also negatively impact the phosphorus cycle
• Climate change can substantially increase future urban runoff volume and peak flow rate (Zahmatkesh et al 2016).
• Zahmatkesh et al 2015 report a potential increase of up to 60% in precipitation in the NYC region by 2030.
• Pyke et al 2011 – Boston scenario for with and without LID vs conventional
• “Burian (2006) assesses drainage infrastructure performance in response to increased precipitation intensity. The results show that upstream parts of urban drainage catchments in the United States may be resilient to precipitation effects of climate change because most development codes have required a minimum pipe size that has resulted in oversized drainage systems. Results also show downstream parts of urban catchments are more affected by in- creased precipitation intensity and thus more susceptible to the effects of flooding from climate change.”  cited in Zahmatkesh et al 2014
• Impacts of weather on buildings, roads, bridges, hydro-transmission lines, stormwater drainage, drinking water and water treatment services, natural gas and communication lines, range from softening of tarmac during summer heat waves and cracking of concrete during freeze-thaw cycles, to catastrophic flooding, road washouts, ice and windstorm damage. The frequency and intensity of all these small- and large-scale effects is changing and infrastructure of all kinds is in danger of becoming subject to conditions for which it was not designed. For example, this means that the environmental performance of some infrastructure, such as wastewater and stormwater infrastructure may become inadequate, which would have impacts on the water quality, water quantity and the ecosystem.  Ontario 2012 (Action Plan)
• “Thus, in order to adapt to the increased winter precipitation expected with climate change, greenspace provision will need to be considered alongside increased storage. There is significant potential to utilize sustainable urban drainage (SUDS) techniques, such as creating swales, infiltration, detention and retention ponds in parks”  Gill et al 2007
• “CC effects were on average two orders of magnitude greater than LU impacts on mean daily stream T. LU change affected stream T primarily in headwater streams, on average up to 2.1°C over short durations, and projected CC affected stream T, on average 2.1-3.3°C by 2060.”  Daraio and Bales 2014 – a modelling study that assesses the effects of land use vs climate change on urban stream temperatures

o Higher temperatures, greater annual precipitation, larger precipitation events, increase in frequency of high flow events. Future climate scenarios predict a 40% increase in future TSS loading. Return periods for critical flows are reduced in future scenarios, while larger storms will be more frequent. Baseflow will decrease with potential impacts on rates of stream aggradation. Increased risk of erosion damages to infrastructure . Stream crossings may need to be larger. Erosion thresholds exceeded more frequently. Greater sediment loading in watercourses. Combines with higher peak flows and lower baseflow, altered sediment transport regimes could change the way our rivers form and adjust. Potential change in vegetation, habitat with increase of invasive species, drying wetlands, stress on fish species in warm and turbid waters.  Karen Hofbauer 2016 NCD 2016 Conference Presentation. Need to contact her in few months to obtain a draft of the study. Based in Hamilton – good local example of potential impacts of climate change to local streams and rivers.

Impact of observed and projected climate change on urban infrastructure

• Stormwater is sensitive to 3 main drivers – amount of impervious cover, precipitation volume and event intensity
• Natural vs built infrastructure
• “Typically, stormwater management practices are designed to meet performance standards based on historical climate conditions. In the coming decades, however, the built environment, including stormwater management systems, may need to meet performance expectations under climatic conditions different from those in recent history (IPCC, 2007; Karl, Melillo, & Peterson, 2009; Milly et al., 2008; USGCRP, 2009)”.  cited in Pyke et al, 2011
• Climate change and urbanization forma vicious circle: you cannot separate the two as they form a loop, whereby urbanization exacerbates climate change, and climate change drives people to urban centers which results in urbanization
• “Over the coming century, climate change scenarios project that urban regions will be expected to manage extremes of precipitation and temperature, increased storm frequency and intensity, and sea-level rise. Increases in problems with which urban areas are already coping may be indicating–or at least mimicking – that climate change impacts are already occurring and are likely to worsen in the future.2 In practice, these impacts will mean coping with: • Longer and hotter heat waves • Increased urban heat island (UHI) impacts such as heat related illness and higher cooling demand and costs • More damaging storms and storm surges • Greater river flooding • Increased frequency and intensity of combined sewer overflows (CSOs) • More intense and extended duration of droughts • Longer water supply shortages, and • Declines in local ecosystem services, such as the loss of coastal wetlands that buffer communities against hurricanes.”  Foster et al 2011
• “With climate change comes an increased risk of intense storms, extreme precipitation events, flooding, and sea level rise (IPCC, 2014). This risk is more pronounced in urban areas due to the preponderance of paved, impermeable surfaces and critical infrastructure such as centralized energy grids and communications systems. Ecosystem-based solutions to this problem provide more permeability, slowing and sinking excess water, which in turn reduces pressure on wastewater treatment systems and diminishes the threat of floods.”  Nichol and Harford 2016
• Soil compaction is likely to reduce baseflows in catchments
• Conventional infrastructure degrades watercourses (Walsh et al 2012)
• “Nonpoint-source pollution, i.e., stormwater runoff in cities, is the main cause of stream water-quality degradation in North America (Environment Canada 2001, Brown and Froemke 2012).”  in Wallace and Biastoch 2016
• “Stormwater management is a second fundamental concern when analyzing the impacts of climate change on regional water systems. The increased intensity and frequency of high- precipitation events will likely result in increased runoff and flooding (Wilby 2007). Additionally, future development locations and land use decisions play influential roles in determining future stormwater runoff impacts regionally. Analyzing future regional stormwater runoff patterns involves considering climate change impacts in conjunction with urban development patterns. One such study, performed on the Rock Creek Basin in Oregon, indicates that, given climate change projections, sprawling development patterns increase annual runoff by 5.5 percent compared to the baseline model, while a more compact development scenario results in increased annual runoff by 5.2 percent (Franczyk and Chang 2009). The researchers conclude that while regional development patterns have a significant impact on streamflow and water runoff, climate change is expected to have a greater impact on streamflow than land use change (Barlage et al. 2002; Chang 2003; Franczyk and Chang 2009). As water runoff has a strong connection to flood risk and damage in urban areas (Ashley et al. 2005), as well as impacts on the health of natural watersheds (Barlage et al. 2002), considering the future effects of climate change is extremely important.”  Larson et al 2011

Becoming a climate-ready region through stormwater management

Mitigation, adaptation and resiliency

• According to The Co-operators (2014), the City of Toronto scored a grade of B- for flood preparedness. Among 16 metrics, the Urban Drainage Maintenance metric scored as one of the lowest, with a grade of D. “Urban drainage maintenance refers to pro-active efforts to ensure that structures such as culverts, sewer grates and storm sewer systems remain clear. Eight cities in the survey have established formalized programs to maintain urban drainage – notably, Vancouver is near completion of an integrated storm water management plan, which will include recommendations for green infrastructure on public and private land.”  The Co-operators 2014
• “Some responders noted that installation of backwater valves provides only a secondary line of defense. Improvements to drainage infrastructure, long term investments into redevelopment of sanitary and storm sewer systems, and the introduction of green infrastructure techniques are also required to protect property from loss.”  The Co-operators 2014
• Bill 72, the Water Opportunities and Water Conservation Act Section 26(2) 4. “An assessment of risks that may interfere with the future delivery of the municipal service, including, if required by the regulations, the risks posed by climate change and a plan to deal with those risks.”  calls for a plan to deal with risks of climate change
• “Characteristics of a resilient urban system are its ability to bounce back from impacts which may include elements of flexibility, diversity, sustainability, adaptability, self- organization, self-sufficiency, and learning.6 However, community resilience and climate adaptation are difficult to assign value, given uncertainties about future climate impacts and the subsequent difficulty in knowing when a community is adequately “adapted.” Multiple goal, no-regrets policies centered on “green-infrastructure” can offer measureable benefits regardless of how climate changes.”  in Foster et al 2011
• Resilience: “The ability of a system to absorb and rebound from weather extremes and climate variability and continue to function.”; Adaptation: “Any action or strategy that reduces vulnerability to the impacts of climate change. The main goal of adaptation strategies is to improve local community resilience.”  Roseen 2008
• “Moreover, adaptation to climate change emphasizes system resilience, which refers to ‘the amount of change a system can undergo and still retain the same function and structure’ (Nelson, Adger, & Brown, 2007, p. 398). Green infrastructure can moderate the adverse impacts of climate change and may enhance our ability to deal with larger-scale extreme weather events. These contributions are usually articulated in terms of resilience, which describes the ability of communities to recover from shocks and return to a functional state within a reasonable timeframe (Pelling, 2011; Renn, 2008).”  Matthews et al 2015
• Paragraph on the definition of resilient, adaptation and mitigation. Good paper on this  Voskamp and Van de Ven 2015
• “Land use management, including LID, will be an important component of strategies for adaptation. Research has shown that the effects of land use and climate change on watersheds can vary, yet the two factors can operate synergistically, increasing the magnitude of stormwater runoff and overall water quality impacts (Chang, 2004; Tu & Xia, 2008).”  cited in Pyke et al 2011
• “Adaptive capacity is defined as the ability of a system to adjust its characteristics or behavior to expand its coping range to respond successfully to climate variability and change. This includes the re-sources available for adaptation as well as the ability of the system to use these resources effectively toward adaptation. Adaptive capacity may be aided or con- strained by factors both inside and outside the community (e.g., social and ecological reasons, cost, state or national regulations, etc.) Social capital is a key component (Brooks and Adger 2005), including the relationships between community members, participation in decision making processes (Moore and Koontz 2003), and the presence of leadership that is willing to advance adaptation objectives (Lowe et al. 2009).”  Tryhorn 2010
• Roseen et al 2011 (study for University of New Hampshire) have an extensive chapter on LID as a climate change adaptation tool and have case study examples
• “It is common to consider adapting stormwater systems to climate change by adding simple uplifts to rainfall intensities and then assessing whether or not the existing system can cope or not (e.g., Defra, 2010; Semadeni-Davies et al., 2008). This is the Predict-Then-Adapt method which begins by considering the changing climate system (drivers) and the consequent pressures (e.g., increased runoff), state (e.g., system performance) to predict the impacts (e.g., flooding and pollution). Responses then need to be formulated to deal with the pressures and impacts in a way that maintains expected levels of performance. This method has been classified as cause-based after its reasoning (Jones and Preston, 2011). The main problem with it is the reliance on estimated climate change scenarios that are expected to provide some precision as regards forecasts of climate change. However, despite past and current scientific advances in climate modelling, there remain large uncertainties about the direction, rate and magnitude of climate change”  Gersonius et al 2012.
• “It should be noted that although the stormwater management initiatives that are proposed to be integrated into Toronto’s street network will not contribute significantly to mitigating the impacts of extreme precipitation events, they will improve the function and resilience of existing stormwater infrastructure by reducing runoff volumes, thereby freeing up capacity within the downstream stormwater drainage system”  City of Toronto 2016 (green streets technical guidelines)

‘No-regrets’ approach

This is an approach referenced in few different studies and seems to fit well with the benefits of LID in light of climate change. Tie back to the fact that climate change projections are uncertain, especially at local scales, so why not implement LIDs – they are practices that work well for stormwater management with and without the effects of climate change.

• Climate change should be considered in future planning but the uncertainty in estimates makes it harder for those involved
• “Acknowledging that there is uncertainty as to how the climate will change and at what rate, the team developed strategies that are built upon three principles which ensure that their recommended actions make sense under any scenario: • Triage: Avoiding efforts that are unlikely to succeed and concentrating on areas where improved management can have the biggest impact; • Precautionary principle: Not waiting for certainty to act where the consequences of potential impacts are high; and • No regrets: Focusing on actions that provide benefits regardless of how the climate changes (Wisconsin Initiative on Climate Change Impacts, 2011).”  Huron River Watershed Council, 2013
• “No-regrets actions are those that provide benefit under both current climate conditions and potential future climate conditions. No-regrets options increase resilience to the potential impacts of climate change while yielding other, more immediate economic, environmental, or social benefits (Heltberg et al, 2008). The no-regrets approach is considered “proactive adaptive management” which is based on the development of a new generation of risk-based design standards that take into account climate uncertainties. There are a wide variety of no- regrets actions that improve the adaptive capacity of the watershed to handle stormwater.” Huron River Watershed Council, 2013
• ‘No-regrets’ strategies “Faced with uncertainty about future climate change, and given constraints on available resources, communities may choose to pursue no-regrets strategies – actions that are beneficial in addressing current stormwater management needs regardless of whether or how climate may change in the future (Means, Laugier, Daw, Kaatz, & Waage, 2010)”. -Cited in Pyke et al 2011. “The results of this study also demonstrate the effectiveness of site redevelopment, including increased density and reduced impervious cover as a no-regrets adaptation strategy for reducing pollutant loads associated with stormwater runoff.”  Pyke et al 2011. “management infrastructure, a challenge that many practitioners and decision makers are just beginning to consider (Blanco, Alberti, Forsyth, et al., 2009; Blanco, Alberti, Olshansky, et al., 2009). Responding to climate change will be complicated by the scale, complexity, and inherent uncertainty of the problem, therefore it is unlikely that this challenge can be solved using any single strategy. The scenario analyses conducted in this study illustrate the potential effectiveness of one common element of LID, reducing impervious cover, in the context of climate adaptation.”  Pyke et al 2011
• “Managing green infrastructure for climate adaptation is primarily about managing risks or uncertainties created by anthropogenic activities. The risk-based approach to climate change has three defining aspects: problem framing and role; embedded policy discourse; and planning approaches. First, problems associated with adverse weather conditions, including rainstorms, floods, heat waves and cyclones, tend to be understood in probabilistic terms. The ‘thing’ that matters is not discrete material benefits that can fulfill the needs of the public, but non-linear, irreducible uncertainties associated with changes in the climate. Functioning as a risk buffer, green infrastructure actually helps minimize the impacts of public ‘bads’ (i.e. natural perils) and, by doing this, indirectly provides public ‘goods’. There is limited precision as to where and when these impacts will eventuate and in what manner. The ‘necessity’ for green infrastructure is thus reduced to a matter of probabilities that are influenced by global climatic dynamic and humanity’s collective actions. It is driven by problems that we seek to avoid and are unable to predict with high level of precision.”  Matthews et al 2015

Water as a valuable resource

Drill down the fact that stormwater is not waste, but rather a resource. It is not in anybody’s interest to get rid of it quickly – move away from the ‘out of sight out of mind’ mindset. Stormwater can be captured, treated and reused and these benefits can be enjoyed by nature, taxpayers, residents, municipalities.

• “Unlike the usual environmental flow problem of needing to allocate a reduced volume of water to the environment, urban stormwater runoff presents a problem of increased runoff volume, which should be prevented from reaching receiving streams and thus could be used by humans….. Urban stormwater runoff is thus revealed as the best type of problem, because solving it provides an opportunity to solve other problems such as the provision of water for human use in cities.”  Walsh et al 2012
• good paper on this by Walsh et al 2012 out of Australia
• “By not harvesting stormwater to keep an appropriate proportion of it out of receiving waters, we not only forego the benefits to society of this large water resource, but also contribute to the degradation of waterways”  Walsh et al 2012
• “Over the past two decades, the paradigm governing urban stormwater management has shifted from strategies that deal with runoff as a waste in end-of-pipe systems to those in which stormwater is viewed as a resource to be infiltrated, stored and/ or re-used at the site (Fletcher et al., 2014; Ahiablame et al., 2013). “  in Vogel et al 2015
• “If a community perceives their stream is a threat (e.g., due to the damage it might cause by flooding), local managers may be pressured to enact policies that degrade a stream’s aesthetic and ecological value (e.g., through installation of formal drainage with high effective imperviousness, and stream burial), unintention- ally reinforcing negative perceptions of the stream as a drain (red loop in the figure). Conversely, if a stream is perceived as a valuable asset, local managers may respond by enacting policies that protect the stream from urbanization, reinforcing positive perceptions of the stream as an asset through increased property value and the provision of green space and other ecosystem services (green loop).”  Askarizadeh et al 2015 –review paper of how LID fits in stormwater management
• “Climate change is likely to reduce precipitation, and therefore runoff, in many parts of the world (Arnell 1999). Reductions in runoff volumes from pervious catchments will be greater than reductions in volumes of runoff from impervious surfaces. Thus, urban stormwater runoff should be a more reliable source of water in response to long-term changes in rainfall patterns. Further- more, the diverse, deeper rooted perennial plant communities that are possible with well-irrigated urban green spaces may also exhibit increased resistance, as they are buffered from the vagaries of our ever harsher climate.”  in Walsh et al 2016
• “stormwater will be considered to be a valuable water resource to be retained and infiltrated into the land within the Built Environment to the fullest extent possible, not a waste product”  Town of Ajax 2016 (Official Plan)

The business case for becoming climate-ready

Floods are expensive and they are expected to increase with climate change; it is worthwhile to invest in flood-mitigating measures to reduce the overall cost of disasters. LIDs could be more cost-effective options even for day-to-day stormwater management.

• Frequency and severity of extreme events is the most costly impact of climate change. Rise in insurance claims due to extreme weather. Taking pro-active measures can help avoid these costs
• “The increased frequency of urban flooding due to climate change is an additional challenge for stormwater systems. Urban flooding not only creates engineering system failures, but directly causes socio-economic loss in the form of: loss of personal property, associated health and safety issues, and psychological stress and distress. Improved management of infrastructure in terms of capital assets, cost reduction, service level, environmental protection, and efficient use of water resource are essential to water infrastructure’s sustainability (Infrastructure Canada 2006; EPA 2012). A necessary step for effective implementation is to assess whether the system is moving towards or away from being sustainable.” Upadhyaya et al 2014
• “Water, wastewater and stormwater infrastructure will re- quire about $400 per household per year to fulfill the investment deficit. A municipal property tax is inadequate to raise the required funds. Therefore, additional federal and provincial funding would be needed.” Upadhyaya et al 2014
• “There are strategies that can be adapted to reduce the risks of flooding while ensuring a minimal economic impact such as revising design criteria based on revised climatic projections, revised acceptable level of risk, and revised life span of infrastructures (Mailhot and Duchesne 2010). The long-term impact was evident, for example, in the flooding that occurred in the city of Peterborough (Ontario) in 2004. It was not realized, until many years after the event, that the actual cost of the flood ranged from $50 million to $300 million (Ontario Center for Climate Impacts and Adaptation Resources 2010) because the actual cost exceeded the projected cost; some of the costs were not visualized beforehand.”  Upadhyaya et al 2014
• “In Canada homeowners can be covered for sewer overflow but they cannot be insured for overland flooding (Sandink et al. 2010). …. The direct and indirect economic bur- dens related to managing stormwaters using inadequate and un- sustainable infrastructure and funding are significant.”  Upadhyaya et al 2014
• “Cincinnati, Ohio has formally agreed to eliminate 85% of its CSO volume in order to better comply with the Clean Water Act. As part of the planning process to comply with the Clean Water Act, a large waste- water storage tunnel was proposed for the Lick Run area. This tunnel was estimated to cost roughly $250,000,000 and have a capacity of roughly 40,000,000 gallons (MSD Cincinnati, 2012). It would have been constructed deep underground in the bedrock beneath the city, connected to existing sewers by dropshafts for transporting water and personnel, and include a pump station and wastewater plant upgrades to facilitate the treatment of its volume. This proposition has been rejected in favor of a plan that includes a type of green infrastructure (GI) called rain gardens. Green infrastructure uses vegetation, soils, and natural processes to infiltrate and evapotranspirate rainwater, as opposed to the engineered collection systems of traditional “grey” infrastructure that capture, treat, and discharge it (USEPA, 2014c).”  in Vineyard et al 2015
• “Garden implementation is heavily favored by higher discount rates due to its cost amortization versus that of the grey alternative. Whereas standard infrastructure requires a large upfront investment and relatively minor maintenance afterward, rain gardens require a proportionally smaller initial investment but (with required upkeep) can include a relatively higher lifetime maintenance cost; this maintenance cost is, however, more straightforward than the unevenly distributed tunnel maintenance. This relationship between cost and discount rate is exacerbated by the long construction time of a storage tunnel compared to the very short startup time of a rain garden.”  in Vineyard et al 2014
• “Insurance premiums are already rising to cover the industry’s rising weather-related losses. So, in light of this new normal, it is shortsighted that all three levels of government seem to be more focused on finding tax dollars to pay for last year’s flood or ice storm instead of addressing the challenge of what to do about next year’s extreme events that we know are coming. Decision makers need to move beyond a reactive stance, and instead forge a proactive plan to improve the resilience of our infrastructure.”  Env Comm of Ontario 2014  they list green infrastructure as a tool that local municipalities use. They critique the current state of stormwater management

LID as a framework for climate-ready city-regions

Provide specific examples of how LIDs are beneficial. Provide references of studies and agencies that promote the use of LIDs.

LIDs as preferred tools

• Zhou 2014 calls for LIDs to mitigate climate change
• Loperfido et al 2014 call for LIDs to mitigate climate change  “In areas predicted to receive more frequent and more intense precipitation events under climate change, distributed BMPs may be an effective means to achieve some reduction in runoff volume during extreme precipitation events as was observed during Tropical Storm Lee.”
• “Although hydrologic improvements provided by distributed BMPs were substantial, land cover appeared to play a dominant role in reducing total runoff volume and decreasing stream response during precipitation events. Thus, it is important to consider land cover factors (e.g., decreased impervious cover and greater forested area) as effective stormwater BMPs with respect to urban stream hydrology in addition to the implementation of distributed BMPs.”  Loperfido et al 2014
• “This paper has provided an assessment of several alternatives in the 7.05 ha catchment of Shockoe Creek adjacent to the SMV. These alternatives included: Existing conditions, Gray (storage infrastructure), Green-Free (free discharge GSI with uncontrolled outlets), and Green-Control (GSI with controlled outlets). In terms of hydraulic performance, Green-Control performed substantially better than Gray. In terms of volume control, however it had slightly more overflow occurrences. In addition, the Green-Control alternative also has much less discharge after the event, reducing treatment plant operational costs. As the additional cost of installing such controls is nearly negligible, these benefits of outlet controls are clearly worth deploying in GSI SCMs. The relative position of both GSI alternatives improved with the altered climate alternative, indicating that they are more resilient than the Gray alternative. Furthermore, the reductions in peak flows by Green-Control are the greatest of all alternatives, providing the most benefits in terms of minimizing nuisance flooding and erosive flows. While the Gray alternative reduced CSO occurrences by the largest number, the larger benefits, smallest overflow volumes, and most resilient system was obtained by the Green-Control alternative. CSO volume is directly related to negative ecological impacts to receiving waters. As such, this study has demonstrated that GSI provides a more sustainable solution to CSOs than gray. Hydraulic control of discharges is strongly recommended for GSI solutions to CSO mitigation.”  Lucas and Sample 2015
• “Insurance premiums are already rising to cover the industry’s rising weather-related losses. So, in light of this new normal, it is shortsighted that all three levels of government seem to be more focused on finding tax dollars to pay for last year’s flood or ice storm instead of addressing the challenge of what to do about next year’s extreme events that we know are coming. Decision makers need to move beyond a reactive stance, and instead forge a proactive plan to improve the resilience of our infrastructure.”  Env Comm of Ontario 2014  they list green infrastructure as a tool that local municipalities use. They critique the current state of stormwater management
• “Third, the effect that retention ponds have on flood frequency diminishes in the downstream direction as the proportion of unregulated subcatchments that contribute to the peak discharge at the outlet also increases. This means that the flood mitigation benefits of flood retention ponds are primarily local, which underscores the added value of distributed flood retention ponds in terms of their ability to disperse the flood control benefits across the catchment.”  Awalew et al 2015 – study on pond configuration in a modelled catchment. Good point to use when claiming that LIDs are better suited to mitigate floods
• “Seattle is currently developing its first comprehensive Climate Preparedness Strategy, which underscores the value of flexible, scalable approaches that allow for adaptive management in the face of climate uncertainties. Distributed GSI installations are one such approach, offering protection against back up risks or other localized pipe capacity issues that are likely to be exacerbated by increased precipitation under climate change. Distributed GSI prevents stormwater from entering the piped system, preserving or enhancing existing capacity. Rainwater harvesting and reuse reduces demand on drinking water supply and may also provide emergency drinking water sources in the case of natural disasters.”  Coven et al 2015
• “Runoff mitigation through emerging approaches like green infrastructure and low impact development can apply this information to design sustainable urban ecosystems [Yang et al., 2013] and to increase the resilience of watershed systems to changing land use and climatic conditions.” Ekness and Randhir 2015
• “While the challenges of stormwater management appear to be vast, overcoming them creates opportunities to make gains beyond just controlling stormwater. This is especially true when incorporating green infrastructure. Combining stormwater controls with other urban planning investments can lead to more vibrant communities, better climate change resilience, and cost savings”……” Communities also can use stormwater controls to improve climate resilience, which is the ability to adapt to and recover quickly from climate-change-related events. Climate”  WEF Stormwater Institute 2015
• Green Infrastructure Ontario states that LIDs provide climate change mitigation benefits (GIO 2012)
• “The modelling work presented here suggests that the use of urban greenspace offers significant potential in moderating the increase in summer temperatures expected with climate change. Adding 10 per cent green in high-density residential areas and town centres kept maximum surface temperatures at or below 1961–1990 baseline levels up to, but not including, the 2080s High.”  Gill et al 2007
• The implementation of LIDs has been identified as a strategy to adapt cities to climate change in a Netherlands paper  Albers et al 2015
• In a 2009 State of the Practice Report produced by TRCA for the Region of Peel called for the implementation of LIDs to mitigate the impacts of climate change. TRCA, 2009
• Studies have found LID to be effective in moderating extreme temperatures and increased surface runoff (Gill et al 2007)
• Calling for an improved assessment of LIDs and how they can mitigate climate change back in 2011 (by Pyke et al 2011). An attempt to address this is done by Zahmatkesh et al 2015 who analyze the impacts of LID related to climate change on a watershed in New York
• An example where LID was recognized to mitigate effects of climate change – in 2012 Hurricane Sandy – Bloomberg and Strickland (2012) acknowledged that GI played an important role in “creating a resilient city that can not only manage its stormwater but recover more quickly from the impacts of climate change.”
• “Gill, Handley, Ennos, and Pauleit (2007) found LID to be effective in moderating potential climate change impacts such as extreme temperatures” cited in Pyke et al 2011
• Landscape and greenspace can lessen the future effects of climate change, site level adaptation strategies are crucial (Larson et al 2011)
• “A study conducted by Zahmatkesh et al. (2015) showed that the introduction of LID had the potential to mitigate the majority of expected runoff increase due to climate change in New York City. Stack et al. (2014) also documented similar potential to reduce flood vulnerability associated with climate change through LID retrofits in Minnesota, though integrating structural LID practices with natural green infrastructure networks showed the greatest resilience to flooding across a range of climate change scenarios. As climate change issues receive greater attention from local governments, the technical evidence base now being developed to demonstrate the flexibility of LID and GI to climactic change could support broader implementation.”  Vogel et al 2015
• “As to the National Post Construction Stormwater Rule, EPA has decided to defer action on rulemaking to reduce stormwater discharges from newly developed and redeveloped sites or other regulatory changes to its stormwater program. Instead EPA is redirecting its efforts to focus on pursuing a suite of immediate actions to help support communities in addressing their stormwater challenges. EPA will provide incentives, technical assistance, and tools to communities to encourage them to implement strong stormwater programs; leverage existing requirements to strengthen municipal stormwater permits; and continue to promote GI as an integral part of stormwater management. EPA believes this approach will achieve significant, measurable, and timely results in reducing stormwater pollution and provide significant climate resiliency benefits to communities.”  Goulding et al 2014

What can LID offer?

The examples below contain multiple examples of what LID can offer in light of climate change and this is why they have not been placed in individual categories below. For example, when talking about the benefits of infiltration and filtration, multiple sources from the list below can be referenced. In some cases where the source talks about one benefit specifically, it has been populated under the specific category.

• “GI primarily benefits the environment by eliminating the need for traditional grey infrastructure and its associated environmental impacts. Green infrastructure can promote improved air and water quality (Nowak et al., 2006; CWP, 2007). GI has the potential to sequester atmospheric carbon, remove atmospheric pollutants, and reduce the urban heat island effect to save energy and money in cooling costs (Odefey et al., 2012). GI can restore natural hydrology, recharge groundwater, eliminate CSO contributions, and slow the flow of stormwater to streams to restore stream health (Dietz, 2007; Davis, 2008; Stephens et al., 2012). Tzoulas et al. (2007) suggests there are considerable social benefits to the urban green space that accompanies GI.”  in Vineyard et al 2015
• “Figure 5 compares the impacts of the Shepherd Creek rain gardens to their grey counterparts. The stormwater storage tunnel and the wastewater treatment plant together emitted more environmental impacts in every category than the base case rain garden. Choosing the green alternative offered important reductions in the eutrophication and global warming categories, which saw 98 and 90% reductions, respectively, according to our model….. They dramatically reduce environmental impacts in every impact category (with the possible exception of ecotoxicity). Of greatest interest are their benefits to both eutrophication and global warming, which they achieve by intercepting nutrient pollution before it can reach the wastewater and by reducing the use of electricity for wastewater treatment..”  Vineyard et al 2015
• “While the benefits of blue-green measures lie in general in the variety of ecosystem services that can be provided [8,9], only a selection of services specifically contributes to adaptation to extreme events. These are the urban ecosystem services (and corresponding climatic hazards): water flow regulation and runoff mitigation (pluvial flooding, drought), urban temperature regulation (heat stress) and moderation of environmental extremes (pluvial flooding, heat stress and drought) [12]. These regulating ecosystem services are provided by ecosystem functions: the bio- physical structures or processes in ecosystems [36]. The ecosystem functions that underlie the ecosystem services of concern are: infiltration, retention in the soil, adsorption on kinetic energy, storage, evapotranspiration and rainfall interception [12,37]. As it differs among blue-green measures if or in which degree these processes are present, the role in adaptation to heat stress, drought and pluvial flooding varies among the measures. Based on the ecosystem functions present, the following blue-green measures are distinguished in this paper: * Storage & harvesting measures, facilitating water retention in the soil, storage or rainfall interception; * Attenuation measures, slowing down runoff during a rainfall event after the storage capacity of the measure has been exceeded; * Infiltration measures, enabling groundwater recharge; * Cooling measures, providing evapotranspiration; see table below for details:
• “The approach seeks to create healthier more socially cohesive and biodiverse urban environments and a connected city ecosystem for people and wildlife that also builds in resilience measures against climate change in the form of storm, flood, heat, drought and pollution protection. The Cities Alive approach seeks to positively utilise the key GI components that lie within our city environments and perform essential ecosystem services. A GI-led design approach aims to create a network of healthy and attractive new and upgraded city environments, sustainable routes and spaces. The approach would build on, strengthen and link existing GI components described above. Over time this resilient and networked “city ecosystem” will be capable of generating a substantial range of social, environmental and economic benefits for urban citizens, whilst also providing protection against the effects of climate change.”  Arup, 2014
• “Seattle has also set an ambitious goal to be a carbon neutral city by the year 2050 and is implementing its 2013 Climate Action Plan to sharply reduce greenhouse gas emissions across all sectors. GSI implementation supports Seattle’s carbon neutrality target in three principle ways: •GSI installations in combined sewer basins reduce pumping and water treatment demand, saving the associated energy and GHG emissions. •The use of compost in bioretention soil mixes and all compost- amended soil replacement triggered by Stormwater Code results in a net increase in soil carbon/sequestration. •Trees planted and retained have direct sequestration value as well as indirect mitigation value via shading.”  Coven et al 2015
• “The core principle of LID is the management of increased runoff typically through filtration and infiltration strategies to provide treatment and reduce runoff volumes. These measures will have similar effects for managing increased storm sizes associated with changing rainfall patterns resulting from climate change.”  Roseen et al 2012
• “Yet adaptation has been slow, mainly because some potential solutions are politically unpalatable (Byrne & Yang, 2009). Other solutions may be expensive, may impact the rights of private property owners, may require major changes to existing planning systems, or may constrain future property development options (Bulkeley, 2013). Green infrastructure however, appears to be relatively quick to implement, is comparatively inexpensive, has broad public appeal, and is politically benign (Bowler, Buyung-Ali, Knight, & Pullin, 2010; Byrne & Yang, 2009). Moreover, it could gain rapid acceptance in an age where planning is increasingly attentive to urban infrastructure (Dodson, 2009).”  cited in Matthews et al 2015
• “Green infrastructure has broad appeal, largely due to its multiple benefits (Emmanuel & Loconsole, 2015; Gill, Handley, Ennos, & Pauleit, 2007; Jim, 2015; Kambites & Owen, 2006). For example, climate change will likely magnify urban heat island effects and increase flood events for many cities (Field, Barros, Stocker, & Dahe, 2012; Lo, 2013). Such impacts will likely be exacerbated by increases in ‘hard’ surfaces associated with rapid urbanization (e.g. concrete, stone, tile, asphalt and tarmac) (Field et al., 2012; Gartland, 2011).”  cited in Matthews et al 2015
• LIDs are not only useful in terms of a climate agenda, but are useful anyway – aesthetic and other socio-economic benefits
• “The biophysical features of greenspace in urban areas, through the provision of cooler microclimates and reduction of surface water runoff, therefore offer potential to help adapt cities for climate change.”  Gill et al 2007
• GI’s benefits are – CO2 reduction, thermal comfort and reduced energy use (green roof given as example), reduced problems with flooding and improved water quality (bioretention as example), effects on air quality, health and restorative benefits, education.  Demuzere et al 2014
• Literature on LIDs to reduce runoff and improving water quality at all scales is substantial ((e.g., Davis 2005; Dietz and Clausen 2005; Fach and Geiger 2005; Hunt et al. 2006; Carter and Jackson 2007; Dietz 2007; Elliott and Trowsdale 2007; Scholz and Grabowiecki 2007; Collins et al. 2008; NRC 2008; Bedan and Clausen 2009; Davis et al. 2009; Hinman 2009; Berndtsson 2010; Fassman and Blackbourn 2010; Roy-Poirier et al. 2010; Zimmerman et al. 2010; Gregoire and Clausen 2011; Hurley and Forman 2011; Myers et al. 2011; Scholz 2011; Rowe 2011;Walsh and Pomeroy 2013).  cited in Zahmatkesh et al 2015
• The use of LIDs to manage the urban runoff problem have been recommended by Walsh et al 2012
• “The temperature benefits of green roofs extend to climate change mitigation as well. Vegetation and the growing medium on green roofs also can store carbon. Modeling has determined that green roofs may reduce building energy use for electricity consumption by 2 - 6% over conventional roofs, particularly for summer cooling.24 One study estimated carbon sequestration at 375 grams per square meter for green roofs. However, because many of the plants are small and the growing medium layer is relatively thin, green roofs tend not to have as large a carbon storage capacity as trees or urban forests.2g”  in Foster et al 2011
• “Other benefits of GI implementation in urban areas may include biodiversity protection, climate change mitigation, water management, and food production (Sussams et al., 2015).”  Vogel et al 2015

Infiltration and Filtration

“In particular, the frequency and magnitude of overflow from the systems substantially increased under the climate change scenarios. As this represents an increase in the amount of uncontrolled, untreated runoff from the contributing watersheds, it is of particular concern. Further modelling showed that between 9.0 and 31.0 cm of additional storage would be required under the climate change scenarios to restrict annual overflow to that of the base scenario. Bioretention surface storage volume and infiltration rate appeared important in determining a system’s ability to cope with increased yearly rainfall and higher rainfall magnitudes.”  Hathaway et al 2014 – modelling study in US to see how bioretention can mitigate climate change.

• “This study shows that the current levels of SGI in two major Mid-Atlantic cities and surrounding areas do have small, but significant to marginally significant and positive impacts on hydrology and nitrogen exports. Specifically, this study found that at the watershed scale, when stormwater green infrastructure controls N5% of drainage area, flashy urban hydrology and nitrogen exports are reduced. The magnitude of impacts are small, but will likely increase with more SGI. There were also some promising trends towards reduced CSO levels with higher SGI in watersheds, but the differences between sewersheds create high variability in CSO levels.”  in Penino et al 2016 – already evidence of improvement

Simultaneous benefits for periods of drought and periods of excess water

“Approaching urban climate adaptation to extreme events in an integrated way, shows that we are dealing with a temporal variation in water surplus (pluvial flooding) and water shortage events (drought and heat stress). Linking water surplus and water shortage events is required in order to buffer temporal variations. To this end storage has to be created [35]. Sufficient storage capacity helps to prevent heavy rainfall events to cause pluvial flooding. In addition, the water stored serves as supply for evaporative cooling to prevent heat stress in times of heat waves and as water source to prevent drought in times of no or little precipitation.”  Voskamp and Van de Ven 2015

• “For combined scenarios of high climate change and high urban development, there is a projected increase in winter flows of up to 71 percent and decrease in summer flows of up to 48 percent.”  cited in Praskievicz and Chang 2012  shows the extremes of climate change
• “We find that in situ and modeling methods are complementary, particularly for simulating historical and future recharge scenarios, and the in situ data are critical for accurately estimating recharge under current conditions. Observed (2011–2012) and future (2099–2100) recharge rates beneath the infiltration trench (1750–3710 mm/yr) were an order of magnitude greater than beneath the irrigated lawn (130–730 mm/yr). Beneath the infiltration trench, recharge rates ranged from 1390 to 5840 mm/yr and averaged 3410mm/yr for El Nino years (1954–2012) and from 1540 to 3330mm/yr and averaged 2430 mm/yr for La Nina years. We demonstrate a clear benefit for recharge and local groundwater resources using LID BMPs. (Newcomer et al 2014)

Retaining pollution from non-point sources

“Work done to reduce nonpoint sources of contaminants to streams needs to consider the realities of not only groundwater inputs and the role of ambient conditions but also the additional stress caused by climate change and other factors like invasive species which can often counteract initiatives taken to improve stream water quality. These considerations only emphasize the need for source control where possible and for monitoring programs which when thoughtfully designed will help determine what can be done to achieve tangible improvement in water quality.”  Long et al 2016 (Hamilton study)

1. Reduced CSOs - Discussion on CSOs – introduction of Vineyards et al 2015 has a detailed explanation of the issue.
2. Reduction of Urban Heat Island Effect
3. CO2 Sequestration
4. Overall ecological benefits

Conventional stormwater drainage has been identified as a primary driver of the commonly observed, severe degradation of stream ecosystems in urban catchments (Walsh et al 2010; Wenger et al 2009)  cited in Walsh et al 2012

Opportunities for LIDs in an already built-up environment

1. Talk about retrofitting opportunities and the benefit of some LID that take up little space
2. Case that our infrastructure is degrading, hard to upkeep, so when we are changing to new infrastructure, change to LID
3. Old infrastructure using old methods

• “The built environment of an existing city is continuously changing by maintenance, modification and renewal. This inherent dynamics of the urban environment provide opportunities for retrofitting blue-green measures synergistically with other structural changes in the urban form [15,28,40,41]. Opportunities for retrofitting arise for instance when existing paved areas are removed for works on cables or for sewer rehabilitation [15,28,41], when buildings are renovated, when infill development takes place [28], and with urban renewal projects [40,41]. Linking implementation of blue-green climate adaptation measures with such ‘windows of opportunity’ is greatly beneficial for a reduction of implementation costs [15].”  Voskamp and Van de Ven 2015

d. Watershed-scale approaches to LID Single LIDs placed scarcely may not be able to tackle climate change. For this reason, there has to be a (sub)watershed scale effort.

o “Retrofitting a single blue-green measure is hardly ever a successful strategy to deal with all relevant climate risks. In order to optimally use the potential of blue-green measures in creating urban resilience to flooding, drought and heat stress combinations of blue-green measures, ‘adaptation sets’, have to be implemented. The composition of an effective and cost efficient package of measures depends on the characteristics of the project site.”  in Voskamp and Van de Ven 2015 o “As explained in paragraph 2.2.1, four vulnerability reduction capacities are required to effectively create resilience: adaptive, threshold, coping, and recovery capacity. An urban area has different levels of these capacities for pluvial and fluvial flooding, heat stress, and drought. Each type of blue-green measure strengthens these capacities in a different way and to a different degree. A combination of measures is required for all-inclusive climate vulnerability reduction. It depends on the current vulnerability of a site which capacities require strengthening most [15] and, accordingly, which combination of measures is most beneficial to increase resilience to extreme events of a particular site.”  in Voskamp and Van de Ven 2015 o LIDs are like a toolbox from which engineers can pick and choose depending on site constraints o “Green infrastructure retrofits, which included street- connected bioretention cells, reduced peak and total stormflow and increased lag times from a suburban residential headwater street. On Klusner Ave, a voluntary participation scheme in which 13.5% of households had rain barrels and rain gardens or street-connected bioretention cells added to their parcels resulted in up to 33% reductions in peak flows, 40% reductions in total storm volumes and desynchronization of peak flow timing compared with an adjacent street where no green infrastructure was installed. Connecting”  Jarden et al 2016, also notes: “The results of this study demonstrate promising effectiveness of catchment-scale green infrastructure retrofits in mitigating stormwater run-off from headwater streets. In particular, connection to streets appears to leverage high value out of a limited number of installations. The site of this study is very typical of mid-20th-century American residential development, suggesting that the results achieved here may be possible to replicate in other areas.” 6. Case studies Specific examples of what agencies and municipalities are doing to make a link between climate change and LIDs and how far they have gone to mitigate climate change through LIDs. Further reading on each document is needed.

Within Ontario

Climate Ready Adaptation Strategy Action Plan 2012. Action 10 | Develop Guidance for Stormwater Management The Ministry of the Environment is currently reviewing best management practices in other jurisdictions in support of proposed Municipal Water Sustainability Planning under the Water Opportunities and Water Conservation Act. The review includes municipal water, wastewater and stormwater systems for additional guidance and information on adapting water systems to deal with impacts caused by climate change. Among system issues and practices being reviewed: • source control (reuse and low impact development) • sewers for conveyance • end-of-pipe treatment works • water conservation • inflow and infiltration • by-passes and combined sewer overflow. . Action 3 | Promote Water Conservation - • applying proactive solutions that encourage groundwater infiltration of stormwater, such as increasing permeable surfaces in built-up areas

MOECC

MOECC 2014 (Ontario’s Climate Change Update) – Glen Murray intro “To keep reducing emissions with a growing population, we need to build for the future. More energy-efficient buildings, smart urban planning, low-carbon transportation options, and green infrastructure are just some of the solutions we need.” MOECC 2015 – (Ontario Climate Change Strategy): “Build green infrastructure to restore eco- systems, reduce atmospheric carbon and protect and expand carbon sinks. Green infrastructure is inter-connected networks of green open spaces that provide a wide range of ecosystem services. Benefits of green infrastructure include cooling communities, reducing the urban heat island effect which, in turn, improves air quality and reduces the impacts of heat stress on our health, preserving biodiversity and pollinator health, capturing and filtering rainwater to reduce flood risk and improve water quality, and promoting carbon sequestration to reduce emissions.”

===City of Toronto City of Toronto Green Streets Guidelines Draft 2016 – “Green streets incorporate green infrastructure into the road rights-of-way to complement or replace grey infrastructure, to build a city that is resilient to climate change and that contributes to an improved quality of life. Green infrastructure as defined in Toronto’s Official Plan refers to “natural and human-made elements that provide ecological and hydrological functions and processes” (Toronto, 2016). Examples of green infrastructure integrated into green streets can include: alternate energy sources, high efficiency lighting, street trees, permeable surfaces, Low Impact Development (LID) stormwater infrastructure and more.”…” Finally, in May of 2016, the Ministry of Municipal Affairs and Housing (MMAH) approved an amendment to policies within the City’s Official Plan (OPA 262) that focuses on climate change, energy conservation, green infrastructure and the natural environment. Adoption of this amendment affects several sections of Toronto’s Official Plan policy framework.”….” The City’s vision was amended to include the following: • a healthy natural environment including clean air, soil, energy and water; • infrastructure and socioeconomic systems that are resilient to disruptions and climate change; and,• a connected system of natural features and ecological functions that support biodiversity and contribute to civic life.”…From Climate Change Adaptation Chapter  “According to Toronto’s Future Weather & Climate Driver Study: Outcomes Report (Senes, 2012), over the coming decades, climate change will produce variable weather patterns throughout the City of Toronto. The study projects some positive outcomes, such as shorter, milder winters with less snow and more rain as well as and longer growing seasons, however it also warns of the occurrence of extreme weather events.”….” The GTSG seeks to assist in climate change adaptation efforts by providing a tool that outlines proper design, construction and care of green infrastructure practices within road rights-of-way that will: • Enhance ecology and reduce heat Island effect; • Protect air quality; • Manage stormwater quality, quantity & efficiency; • Reduce greenhouse gases and promote energy efficiency.”….” Unlike conventional stormwater management systems, some LID practices have the potential to be expanded to provide additional storage capacity. This will be of critical importance for ensuring that Toronto remains a resilient City in spite of potential future changes in precipitation volumes and patterns that may occur as a result of climate change.”….. o Based on these predictions, the City of Toronto should take aggressive action immediately to not only reduce greenhouse gas (GHG) emissions, but also to adapt to changes that will be imminent in the coming decades. The City of Toronto defines climate change adaptation as “initiatives and measures taken to reduce the vulnerability of natural and human systems to actual or expected climate change effects.” Some notable examples of “adaptive actions” already being implemented in the City include: • Increasing the size of storm sewers and culverts to handle greater volumes of runoff; • Increasing the frequency of inspection and maintenance of culverts both as part of a routine inspection program and after storm events; • Changing the slope of the land at the lot level to direct runoff away from property that can be damaged by excess surface water; • Installation of basement backflow preventers and window well guards to reduce flooding risks; • Using cool/reflective materials on the roofs of homes and buildings to reduce urban heat island effect.

York Region

The Region is increasing its efforts to combat climate change, including adopting best practices for infrastructure design. Other strategies include: • Improve hydrological data collection • Use of models and monitoring localized effects • More frequent monitoring and maintenance • Improve bridge, road and culvert design to be more climate change resistant  York Region Transportation Master Plan 2016

Town of Ajax

The Official Plan for Ajax has extensive content and calls for the promotion of LIDs to treat SW. they also mention that new infrastructure needs to be sized properly, although they do not specially say if there are new requirements.  Town of Ajax 2016

City of Ottawa

Ottawa (Boliviar Philips 2013): “Green infrastructure and low impact development (LID)10 have many common elements with the objectives of stormwater management adaptation; however, like existing measures and no regret actions, techniques and the promotion of green infrastructure/LID was well developed in some jurisdictions when climate change, mitigation and more recently adaptation began to be considered at the municipal level. The City’s Infrastructure Master Plan promotes green infrastructure however the scope of promotion is limited to giving “greater consideration” to green infrastructure in the context of capacity management of urban systems. This level of commitment is very different from other cities including a number of cities in the northeastern United States with similar climate, anticipated climate change impacts and infrastructure profiles as Ottawa. Some cities have adopted and are moving forward aggressively with green infrastructure plans as a cost effective (and some assert cost saving) plan to address infrastructure deficits, combined sewer overflows, water resource improvements and climate risks .11 The success of these green infrastructure plans is worth noting as a possible avenue for stormwater management adaptation (and many other no regret benefits) in Ottawa and is discussed further in Section 9 (pg. 44).”

Thunder Bay

Thunder Bay – “Climate-ready city: City of Thunder Bay climate adaptation strategy” 2015. Stormwater management is one of 5 areas of adaptation efforts: The way stormwater is managed will be crucial as extreme weather events increase in frequency and intensity. The City's Stormwater Management Master Plan will consider climate change impacts and focus on resilient Low Impact Development (LID) and Green Infrastructure to reduce and treat stormwater while also delivering many other benefits to the community. GOAL 4. CONSIDER CLIMATE CHANGE IMPACTS IN THE DESIGN, CONSTRUCTION AND MAINTENANCE OF PHYSICAL INFRASTRUCTURE WHILE CONSIDERING AFFORDABILITY AND CO- BENEFITS: Objective 4.1 Incorporate new technology and best practices in the design, construction and maintenance of new municipal infrastructure and facilities to minimize service disruption and increase resiliency. Objective 4.2 Identify retrofit opportunities for municipal infrastructure to minimize service disruptions related to extreme weather events. Objective 4.3 Investigate areas of priority to incorporate best practices and green infrastructure into community and land- use planning and design. The hectares of catchment areas of LID sites is an indicator of Goal 4. Develop education and communication materials promoting the use and benefits of green infrastructure. Prepare a tool kit or resource kit for City administration with information on available best practices and latest innovations in green infrastructure relating to community and land-use planning and design.

Other Jurisdictions

IPCC

IPCC 2014 Summary for Policymakers calls green infrastructure an structural/physical adaptation measure to “Urban floods in riverine and coastal areas, inducing property and infrastructure damage; supply chain, ecosystem, and social system disruption; public health impacts; and water quality impairment, due to sea level rise, extreme precipitation, and cyclones” “Acknowledging that there is uncertainty as to how the climate will change and at what rate, the team developed strategies that are built upon three principles which ensure that their recommended actions make sense under any scenario: • Triage: Avoiding efforts that are unlikely to succeed and concentrating on areas where improved management can have the biggest impact; • Precautionary principle: Not waiting for certainty to act where the consequences of potential impacts are high; and • No regrets: Focusing on actions that provide benefits regardless of how the climate changes (Wisconsin Initiative on Climate Change Impacts, 2011).”  Huron River Watershed Council, 2013  green infrastructure can mitigate the impacts of extreme events which are predicted to be more common as climate changes

US EPA

US EPA (2016) Stormwater Management in Response to Climate Change Impacts: Lessons from the Chesapeake Bay and Great Lakes Regions – “This report provides specific examples of tools, data, methods, and actions to help stormwater managers, community environmental decision makers, and land use planners incorporate climate change into their management plans. Climate changes (e.g., the amount, timing, and intensity of rain events, droughts, and other extreme events), along with land use changes (e.g., development), can affect the amount of stormwater runoff to be managed. Local decision makers have stated a need for more information on how they can adapt local stormwater management planning and stormwater control to account for these changes.” They propose GI and LID as ways to adapt and be resilient to climate change. Some of the goals of the held workshops were : Explore stormwater management adaptations to climate and land use changes in the Chesapeake Bay watershed, particularly green infrastructure or other LID strategies. Lots of mention of GI and LID in this report with respect to dealing with climate change.

New York City

New York City – “New York City has created a Green Infrastructure Plan and is committed to goals that include the construction of enough green infrastructure throughout the city to manage 10% of the runoff from impervious surfaces by 2030.”  cited in Mellilo et al 2014 Zahmatkhesh et al 2015 – NYC modelling study of LID vs no LID scenarios. Based on the model results, it was observed that future runoff volumes increased in comparison to historical runoff volumes due to expected increase in rainfall. The monthly runoff volumes decreased when looking at the with-LID scenarios. Runoff increases by 44% under a projected scenario without LIDs, while runoff decreases by 17% for with-LIDs scenario. “Although the effect of LID implementation on projected runoff based on the maximum scenario was not considerable, future runoff corresponding to a 25-year return period for the mean P scenario will correspond to a 50-year event, and runoff corresponding to 5-year return period for minimum scenario will correspond to a 25-year event, for the same scenarios after using LIDs. The de- crease in runoff reduction was more for climate scenarios that had less precipitation for the future time period. Among the implemented LID types, porous pavement was noted to have the greatest effect on peak flow reduction. In summary, faced with uncertain future weather conditions considering the adverse impacts of cli- mate change, LIDs can provide mitigation benefits.” “New York City is adopting this new stormwater rule to reduce the adverse impacts on City sewers from runoff during rainstorms that are more severe than combined sewers are designed to handle and, to the greatest extent possible, maximize the capacity of these systems. Sewer overflows, floods, and sewer backups can occur when excessive stormwater from impervious surfaces enters too quickly into the combined sewer system. The new Stormwater Rule will allow the City to more effectively manage stormwater runoff from new developments and alterations in combined sewer areas by reinforcing, specifying and prescribing the methods and standards for the application, permitting, construction and inspection of sewer connections to the City sewer system. DEP expects the rule to: ● slow the flow of stormwater from sites, ● mitigate flooding and sewer backups, ● protect the sewer system, and, ● mitigate combined sewer overflows.” The new rule is: “For a new development, the Stormwater Release Rate will be the greater of 0.25 cubic feet per second (cfs) or 10% of the Allowable Flow, unless the Allowable Flow is less than 0.25 cfs, in which case the Stormwater Release Rate shall be the Allowable Flow. (Allowable Flow means the stormwater flow from a development that can be released into an existing storm or combined sewer based on existing sewer design criteria.)”  The City Record, January 4, 2012, NYC (mode detail on this new rule is found in this document). More info found in http://www.sprlaw.com/new-york-city-adopts-new-stormwater-performance-standards-for-development-projects/

Philadelphia

City of Philadelphia Green Streets Design Manual 2014 – “As we witness the effects of climate change causing storms of greater frequency and severity, the green infrastructure we build on our streets is an added safeguard that can help mitigate flash flooding during such events.” City of Philadelphia – “In 2006, the Philadelphia Water Department began a program to develop a green stormwater infrastructure, intended to convert more than one-third of the city’s impervious land cover to “Greened Acres”: green facilities, green streets, green open spaces, green homes, etc., along with stream corridor restoration and preservation.”  cited in Melillo et al 2014

Seattle

“Seattle has also set an ambitious goal to be a carbon neutral city by the year 2050 and is implementing its 2013 Climate Action Plan to sharply reduce greenhouse gas emissions across all sectors. GSI implementation supports Seattle’s carbon neutrality target in three principle ways:•GSI installations in combined sewer basins reduce pumping and water treatment demand, saving the associated energy and GHG emissions.•The use of compost in bioretention soil mixes and all compost- amended soil replacement triggered by Stormwater Code results in a net increase in soil carbon/sequestration.•Trees planted and retained have direct sequestration value as well as indirect mitigation value via shading.”  Coven et al 2015 Seattle – How Does it Work? Green Stormwater Infrastructure In Seattle: Implementation Strategy 2015-2020 (Coven et al 2015). Adopted resolution that GSI is a critical aspect of sustainable drainage system, some examples of text are: WHEREAS, GSI reduces the strain on the City’s sewer system and stormwater system and preserves system capacity, which will be important in managing Seattle’s growth and the potential precipitation impacts from climate change; and WHEREAS, the Green Ribbon Commission, charged with developing climate action recommendations for inclusion in the next version of Seattle’s Climate Action Plan, has identified enhancing the resilience of Seattle’s drainage system as a critical climate adaptation measure and has recommended (as a quick start action) the adoption of a green stormwater infrastructure policy that affirms GSI as the preferred stormwater management tool and articulates pathways for multi-agency implementation; and WHEREAS, GSI can provide additional community benefits, such as increased tree canopy, improved pedestrian safety, new small business opportunities, improvement to streetscapes or bikeways that provide appreciable economic and aesthetic value, and climate mitigation and adaptation value…… <this report greatly ties climate change to GSI and gives examples of successful projects> “Using smart operational fixes – like adjusting weirs and directing flows strategically – helps the existing drainage system perform as optimally as possible. Operational adjustments can be used to address a range of pipe capacity issues like back-ups, flooding, and overflows. Seattle and King County are investing significantly in inter-agency coordination to increase operational excellence and efficiency.”  Coven et al 2015 Seattle – How Does it Work? Green Stormwater Infrastructure In Seattle “Regulatory Requirements Stormwater Code Seattle was one of the first cities in the U.S. to require GSI as part of new development and redevelopment site mitigation. Now, as part of the new 2015 NPDES permit, Washington State Department of Ecology has required the use of low impact development (LID) and GSI statewide, documenting broad concurrence on the ecological and social benefits of these stormwater management practices. Seattle requirements are being revised slightly to align with these new state requirements and are expected to be adopted in January 2016. (For a summary, please see Table 13, page 27.)” “Low Impact Development (LID) Code Integration - Under the new state-issued Municipal Stormwater Permit , Seattle must review, revise, and update its development-related Codes and standards to make low impact development the default approach to site planning and land development. The three key LID principles articulated in the Permit requirement are: minimizing impervious surface; minimizing stormwater runoff; preserving native vegetation. This broad-reaching requirement is driving changes to documents such as Land Use Code, the Right-of-Way Improvement Manual, the Fire Code, Standard Plans and Specifications, and the Municipal Stormwater Code.

Portland

Portland Oregon – updated the city code to require on-site management for new and re-development. “Titles 24 and 25 (Building and Plumbing Regulations) State building and plumbing code requirements are implemented through the Bureau of Development Services during the development review process for private property. BDS approves private parking and driveway surfaces (see Portland City Code 24.45), flood hazard areas (see Portland City Code 24.50), and installation of private downspouts, pipes and sewers, including those that lead to or from stormwater management facilities.”  Portland Stormwater Management Manual 2016 “Many of the actions that help prepare for climate change are already underway today because they benefit the community in other ways. One example is Portland’s long-established regulations and practices to protect, manage, and expand the City’s green spaces and urban forest. These efforts help to improve air quality and reduce the urban heat island effect, which in turn improves comfort and saves energy and money by reducing the need for air conditioning. To reduce flooding and improve stormwater management, significant work has been done to acquire and restore natural areas and floodplains, and to install green infrastructure such as bioswales and ecoroofs. In addition, the development of Portland’s groundwater well system not only supplements the region’s primary drinking water supply, the Bull Run watershed, but also improves Portland’s resilience to withstand potential impacts to the water supply system due to current climate variability as well as future climate change.”  City of Portland and Multnomah County 2014 (Climate change preparedness plan) “Review city codes and drainage rules to evaluate their ability to protect and improve stream flows, seeps, springs, wetland function, water quality including temperature, vegetation and habitat, and stormwater management during hotter, drier, summers. Use the Natural Resource Inventory and other data to track gains and losses, and propose revisions as necessary. Evaluate and pilot planting native species that are currently considered to be at the “northern” edge of their range in Portland.”  City of Portland and Multnomah County 2014 (Climate change preparedness plan) year 2030 Objective 4 (Increase the resilience of natural systems to adapt to increased temperatures and drier summers.) “Better manage stormwater by reducing the overall impervious area (currently 34 percent) within the city through depaving, green infrastructure (greenstreets, ecoroofs, trees, and raingardens), and expanding the urban forest canopy, natural areas and open space. Encourage or require private property owners and developers to implement climate change preparation measures, including limiting or reducing impervious area at site-specific and district scales.” Also “Develop the Stormwater Systems Plan, and update the Stormwater Management Manual and the drainage rules to better manage increased winter precipitation, including reevaluating the modeled “24 hour” storm event design standard. “  City of Portland and Multnomah County 2014 (Climate change preparedness plan) year 2030 Objective 6 (Increase the resilience of the natural and built environment to more intense rain events and associated flooding.) “Begin rainfall event-based monitoring of sediment accumulation in pipes and stormwater facilities”  City of Portland and Multnomah County 2014 (Climate change preparedness plan) year 2030 Objective 12 (Improve monitoring, evaluate effectiveness of climate change preparation actions and advance new research to support climate change preparation efforts.)

Others

• Pyke et al 2011 – similarly to Zahmatkesh et al 2015 but for Boston, they found that the with-LID scenario was superior for managing runoff – 29% less runoff than conventional scenario.
• Pennsylvania – “Enacted polices to encourage the use of green infrastructure and ecosystem-based approaches for managing storm water and flooding.”  in Mellilo et al 2014
• US 3rd National Climate Assessment (Melillo et al 2014) – Key Message 11: Adaptation Opportunities and Challenges – green infrastructure listed as on the adaptation strategies. “Increasing resilience and enhancing adaptive capacity provide opportunities to strengthen water resources management and plan for climate change impacts. Many institutional, scientific, economic, and political barriers present challenges to implementing adaptive strategies.”
• City of Moncton – Climate Change: Adaptation and Flood Management Strategy (2013) – an adaptation strategy listed is “Adopt zero-net stormwater policies and regulations in order to reduce the quantity of stormwater run-off”
• Lake Champlain Basin Program (2015) recommends the use of LID as an adaptation strategy  “be located outside of established flood hazard zones. As new development occurs, the conservation of functioning ecosystems, widespread adoption of GSI and LID practices, and awareness of the impacts of flooding are fundamental climate-ready tools. Training and funding for implementation of better management practices is necessary to prepare for future changes.”

Temperature

Increases in temperature will affect evapotranspiration

Rainfall patterns

Rainfall patterns are forecast to change . Intensity-Duration-Frequency (IDF) curves have been forecast for a number of urban areas in Southern Ontario

Vegetation

Increased atmospheric CO₂ levels will stimulate photosynthetic processes, increasing phosphorus uptake of all plants.

For further information

Reach out to our colleagues at the Ontario Climate Consortium.

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Any form of rain or snow.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

A parameter that describes the capability of a medium to transmit water.

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.

The point, location, or structure where wastewater or drainage discharges from a sewer pipe, ditch or other conveyance to a receiving body of water.

The continuous movement of water from the oceans to the atmosphere (by evaporation), from the atmosphere to the land by condensation and precipitation, and from the land back to the sea (via groundwater and stream flow); also referred to as hydrologic cycle.

A biological community, including humans and their natural environment.

(a) A natural well-defined channel produced wholly or in part by a definite flow of water and through which water flows continuously or intermittently. Also, a ditch, canal, aqueduct, or other artificial channel for the conveyance of water to or away from a given place, as for the draining of a swamp.

(b) A stream or current of water. Legally, a natural stream arising in a given drainage basin but not wholly dependent for its flow on surface drainage in its immediate area, flowing in a channel with a well-defined bed between visible banks or through a definite depression (as a ravine or swamp) in the surrounding land, having a definite and permanent periodic supply of water (the stream may be intermittent), and usually, but not necessarily having a perceptible current in a particular direction and discharging at affixed point into another body of water.

(c) A legal right permitting the use of a flow of a stream (especially of one flowing through one’s land) or the receipt of water discharged upon land belonging to another.

Surface runoff from at-grade surfaces, resulting from rain or snowmelt events.

The rate of rainfall in millimeters per hour.

Any form of rain or snow.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

Relating to the properties, distribution and effects of water on and below the earth’s surface, and in the atmosphere.

The delivery of a disproportionately large load of pollutants during the early part of storms due to the rapid runoff of accumulated pollutants. The first flush of runoff has been defined several ways (e.g., 10 mm per impervious area).

Initial pulse of stormwater runoff which picks up the pollutants that have settled on surfaces during the dry period. The first flush contains the highest pollutant concentrations.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Natural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

The temporary storage of stormwater to control discharge rates, and allow for sedimentation.

Referring to the source of a stream or river.

Total suspended solids

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

The changing of land cover and land uses from rural to urban; the growth of urban settlements.

A biological community, including humans and their natural environment.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

Ground depression acting as a flow control and water treatment structure, that is normally dry.

Natural vegetation and vegetative technologies in urban settings such as: urban forests; green roofs; green walls; green spaces; rain gardens; bioswales; community gardens; natural and engineered wetlands and stormwater management ponds; and porous pavement systems. These systems are designed to provide multiple benefits, such as moderate temperatures, clean air and water, and improve aesthetics.

Natural vegetation and vegetative technologies in urban settings such as: urban forests; green roofs; green walls; green spaces; rain gardens; bioswales; community gardens; natural and engineered wetlands and stormwater management ponds; and porous pavement systems. These systems are designed to provide multiple benefits, such as moderate temperatures, clean air and water, and improve aesthetics.

A system flow of gully inlets, pipes, overland flow paths, open channels, culverts and detention basins used to convey runoff to its receiving waters. City of Toronto 45 Wet Weather Flow Management November 2006

Watercourses and Lake Ontario, to which Stormwater and Combined Sewer Overflows discharge.

A discharge to the environment from a combined Sewer system that occurs because of a precipitation event when the capacity of the interceptor sewer or treatment plant is exceeded. It consists of a mixture of sanitary wastewater and Stormwater runoff.

Green infrastructure

A lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

The greatest volume of stream flow occurring during a storm event.

A body of water smaller than a lake, often artificially formed.

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Toronto and Region Conservation Authority

The technique of removing pollutants from runoff as it infiltrates through the soil.

The addition of water to ground water by natural or artificial processes.

The infiltration and movement of surface water into the soil, past the vegetation root zone, to the zone of saturation or water table.

The water below the surface, and typically below the groundwater table.

The attachment of gas, vapour or dissolved matter onto the surface of solid materials.

The quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/day

The combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.

The interception, storage and eventual evaporation of rainfall from vegetation canopies.

Reduction of peak flow and increase of the duration of the flow event.

Increases in groundwater storage by natural conditions or by human activity. See also artificial recharge

The inflow of surface water to a groundwater reservoir or aquifer.

Ground depression acting as a flow control and water treatment structure, that is normally dry.

Decayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

Land owned by private individuals or companies.

A mixture of mineral aggregates bound with bituminous materials, used in the construction and maintenance of paved surfaces.

A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.

The technique of removing pollutants from runoff as it infiltrates through the soil.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

The rate at which stormwater percolates into the subsoil measured in inches per hour.

The total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds.

A practice or structural measure that is usually implemented at the beginning of a drainage system or at the lot level, to reduce the volume of runoff and minimize the concentration of pollution in overland flow from private property and prevent pollutants from entering Stormwater runoff or other environmental media, as described by the Ministry of Environment.

The drainage area of a river.

An area of land that drains into a river or a lake. The boundary of a watershed is based on the elevation (natural contours) of a landscape.

State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.

Reduction in applied water due to more efficient water use such as implementation of Urban Best Management Practices or Agricultural Efficient Water Management Practices. The extent to which these actions actually create a savings in water supply depends on how they affect net water use and depletion.

A discharge to the environment from a combined Sewer system that occurs because of a precipitation event when the capacity of the interceptor sewer or treatment plant is exceeded. It consists of a mixture of sanitary wastewater and Stormwater runoff.

Low impact development is a stormwater management and land development strategy applied at the parcel and subdivision scale that emphasizes conservation and use of on-site natural features integrated with engineered, small scale hydrologic controls to more closely mimic pre-development hydrologic functions.

A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

The treatment of urban runoff as close to the source area as possible through application of small scale stormwater management practices on individual properties that are linked to downstream conveyance and end-of-pipe practices.

The drainage area of a river.

An area of land that drains into a river or a lake. The boundary of a watershed is based on the elevation (natural contours) of a landscape.

Defined as those plants (including grasses, herbaceous species, shrubs, vines and trees) that have historically existed within a particular area. Native plants have co-evolved with the local ecosystems and natural processes.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

A vegetated area such as a bog, fen, marsh, or swamp, where the soil or root zone is saturated for part of the year.