Climate Trends in Ontario
Observed to date
- IDF: Changing rainfall intensities affect stormwater runoffThat potion of the water precipitated onto a catchment area, which 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. timing, peak rates and volumes; Methods have been relying on static IDF curves. Increased frequency of 12% and increase intensity of 16% of extreme precipitationAny form of rain or snow. events for 1958 - 2007 for the US Northeastern region 
- “Percent changes in the amount of precipitationAny form of rain or snow. 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 precipitationAny form of rain or snow. being concentrated in very heavy events, particularly in the Northeast US (71 %) and Midwest US (37 %).” 
- “As for the temporal trends, significant warming trends are detected throughout the province of Ontario 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 precipitationAny form of rain or snow. (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.”
- “Extreme downpours are now happening 30 % 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 precipitationAny form of rain or snow., on average.” 
- “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 
- “Increases in the frequency and magnitude of extreme rainfall events have been documented in New York State. These changes are among the largest seen within the United States (DeGaetano 2009). Climate change projections suggest that these increases will continue 
- Increase in frequency and intensity of extreme precipitationAny form of rain or snow. events between now and 2100 
- “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 °C in the 2030s,
- 4.0 - 4.7 °C in the 2050s, and
- 5.9 - 7.4 °C in the 2080s.
Likewise, the annual total precipitationAny form of rain or snow. 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 intensityThe rate of rainfall in millimeters per hour.–duration–frequency (IDF) curves are developed to help understand the effects of global warming on extreme precipitationAny form of rain or snow. 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.” 
- “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.”
- 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)
- PrecipitationAny form of rain or snow. 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 precipitationAny form of rain or snow. 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 precipitationAny form of rain or snow. intensity; however, is unclear. It is recommended that a conservative approach should be taken in planning and adapting for extreme precipitationAny form of rain or snow. 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 precipitationAny form of rain or snow. over summer months and significant increases in temperatures.”
- “If winter precipitationAny form of rain or snow. falls as rain instead of snow, which may actually occur more frequently in temperate 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 runoffThat potion of the water precipitated onto a catchment area, which 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. events.” “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 sedimentsSoil, 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..”
- “Dominguez et al. (2012) found increases in the intensity of 20- and 50-year return period winter precipitationAny form of rain or snow. events over the western United States, while over Canada, Mailhot et al. (2012) showed that the intensity of annual maxima precipitationAny form of rain or snow. would increase, with the largest increases for Ontario, the Prairies and Southern Quebec.”
- “The hydrologicalRelating to the properties, distribution and effects of water on and below the earth’s surface, and in the atmosphere. response to climate change was investigated through stormwater runoffThat potion of the water precipitated onto a catchment area, which 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. 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 flushThe 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. (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.”
- “The potential consequences of climate change for phosphorus 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 phosphorus under eutrophic conditions, greater seasonal variability in runoffThat potion of the water precipitated onto a catchment area, which 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. volumes, carbon and nutrient inputs from terrestrial sources (e.g. more winter runoffThat potion of the water precipitated onto a catchment area, which 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. and less summer runoffThat potion of the water precipitated onto a catchment area, which 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.), 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 runoffThat potion of the water precipitated onto a catchment area, which 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. volume and peak flow rate. "a potential increase of up to 60% in precipitationAny form of rain or snow. in the NYC region by 2030". 
- Pyke et al 2011 – Boston scenario for with and without LIDLow 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. vs conventional
- “Burian (2006) assesses drainage infrastructure performance in response to increased precipitationAny form of rain or snow. intensity. The results show that upstream parts of urban drainage catchments in the United States may be resilient to precipitationAny form of rain or snow. 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 precipitationAny form of rain or snow. 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 drainageNatural or artificial means of intercepting and removing surface or subsurface water (usually by gravity)., 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 ecosystemA biological community, including humans and their natural environment.. 
- “Thus, in order to adapt to the increased winter precipitationAny form of rain or snow. 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, detentionThe temporary storage of stormwater to control discharge rates, and allow for sedimentation. and retention ponds in parks” 
- “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 headwaterReferring to the source of a stream or river. 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.” 
- Higher temperatures, greater annual precipitationAny form of rain or snow., larger precipitationAny form of rain or snow. events, increase in frequency of high flow events. Future climate scenarios predict a 40 % increase in future TSSTotal suspended solids loadingThe 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.. 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 sedimentSoil, 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. loadingThe 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. in watercourses. Combines with higher peak flows and lower baseflow, altered sedimentSoil, 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. 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.
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 stormwaterSurface runoff from at-grade surfaces, resulting from rain or snowmelt events..” These uncertainties require a process for continuously assessing the adapted measures, as well as assessing the physical facilities or infrastructures affected by these adaptations.” 
- 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" 
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 runoffThat potion of the water precipitated onto a catchment area, which 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. to be produced under such conditions – particularly when rain falls which exceeds a soil’s hydraulic conductivityA parameter that describes the capability of a medium to transmit water. - the production of stormwater is exacerbated in urban areas where the overwhelming majority of surfaces are imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.. The problems associated with managing stormwater volumes are exacerbated when dense storm sewer networks efficiently convey stormwater runoffThat potion of the water precipitated onto a catchment area, which 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. volumes from a large contributing upland area to a single outlet location, such as a storm-sewer outfallThe point, location, or structure where wastewater or drainage discharges from a sewer pipe, ditch or other conveyance to a receiving body of water. 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 precipitationAny form of rain or snow. 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.
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/hr. 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.
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 cycleThe 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. 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 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 ecosystemA biological community, including humans and their natural environment. 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(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..
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