Data vs Cartoon Infographics? Ontario Extreme Rainfall Data Trends Show Increases and Decreases, Contradicting Environmental Commissioner of Ontario 2017 Report

ECO Report uses a cartoon call-out to explain climate change trends
in Ontario but fails to provide any data to support statements regarding
historical storm trends. Data tells a different story on storm trends.

The Environmental Commissioner of Ontario (ECO) has released her 2017 Greenhouse Gas Progress Report, Ontario’s Climate Act: From Plan to Progress, to the Ontario Legislature.

The report fails to acknowledge extreme rainfall trends in Ontario, ignoring trends identified by the academic community and fundamental information in the official Engineering Climate Datasets.

Chapter 9 indicates:

"Abstract
Here in Ontario we are already feeling the effects of climate change. Higher average temperatures, more climate extremes and the increased incidence of drought, storms, and unseasonable temperatures are affecting people across the province."

ECO has relied on cartoonish data previously in describing climate change issues, but the ECO infographics contradict engineering data used for infrastructure design and flood risk assessments. Toronto observed annual maximum rainfall trends have been decreasing for durations of 5 minutes to 24 hours.

Unfortunately, local data does not support ECO's stated increased incidence of storms. In fact Engineering Climate Datasets show twice as many statistically significant decreasing annual maximum rainfall trends as increasing ones - these are the observed, measured, documented data trends:

Short duration rainfall in southern Ontario shows many statistically decreases for duration of 2 hours or less and only one statistically significant increase. There are several statistically significant decreases for 5 to 15 minute durations but no increases for the shortest rainfall durations. 

The ECO report exercises an "Availability Bias" to characterize storm incidence stating "  The Toronto floods in 2013, the 2014 floods in Burlington and parts of eastern Ontario, and those experienced on the Toronto Islands, in Windsor, in Cambridge, in Minden and in the Ottawa-Gatineau region in 2017, are all the types of events that climate change makes more likely." Evidence-based policies should instead rely on data to characterize extreme weather risks as opposed to anecdotal lists.

July 8, 2013 was a record rainfall for July 8ths but
daily maximum rainfall has been decreasing.

Despite the fact Toronto experienced a flood in 2013, Toronto rainfall extremes have not increased. The chart at right shows that the 2013 maximum rainfall while above average is still part of a decreasing trend since the 1940's. Media report July 8, 2013 as a record .. which is true for all historical July 8ths - but nobody designs infrastructure for rainfall on particular calendar days. Too often, median and non-technical reports confuse the incidence of flooding with that of extreme rainfall - correlation is not the same as causation when it comes to rain and flooding, as urbanization has significantly increased flooding, despite clear stationary extreme rainfall trends.

Academic research published in the International Journal of Environmental Research, Changes in Rainfall Extremes in Ontario relies on data and peer-reviewed analysis to characterize extreme rain - that rigorous approach indicates no obvious regional pattern:

"Abstract

Many Ontario Extreme Rainfall Trends are decreasing especially in
south west and south east regions.

There is a general consensus that climate change has impact on the intensity and frequency of rainfall events. However, very little research is available about the changes in short term rainfall extremes. The focus of this paper has been on the change in annual and monthly rainfall extremes in Ontario. The results indicate a greater variability (increase and decrease) among stations for shorter durations (15-min, 30-min, and 60-min). There is no obvious regional pattern with possible exception of increasing trends at north-western locations."

The table from the paper below shows that Southwest Ontario and Southeast Ontario rainfall has been decreasing at many climate stations, including many statistically significant decreasing trends. Similar to the Environment and Climate Change Canada's Engineering Climate Datasets, there are more statistically significant deceases than increases.

Extreme rainfall trends in Ontario show decreases and increases.

Climate-driven variability in the occurrence of major floods across North America and Europe - Journal of Hydrology Review

An assessment of major flood trends was conducted by a group of researchers including Environment and Climate Change Canada and University of Waterloo Civil and Environmental Engineering. They found no evidence that climate change has to date increased the occurrence of floods.

"Abstract:
Concern over the potential impact of anthropogenic climate change on flooding has led to a proliferation of studies examining past flood trends. Many studies have analysed annual-maximum flow trends but few have quantified changes in major (25–100 year return period) floods, i.e. those that have the greatest societal impacts. Existing major-flood studies used a limited number of very large catchments affected to varying degrees by alterations such as reservoirs and urbanisation. In the current study, trends in major-flood occurrence from 1961 to 2010 and from 1931 to 2010 were assessed using a very large dataset (>1200 gauges) of diverse catchments from North America and Europe; only minimally altered catchments were used, to focus on climate-driven changes rather than changes due to catchment alterations. Trend testing of major floods was based on counting the number of exceedances of a given flood threshold within a group of gauges. Evidence for significant trends varied between groups of gauges that were defined by catchment size, location, climate, flood threshold and period of record, indicating that generalizations about flood trends across large domains or a diversity of catchment types are ungrounded. Overall, the number of significant trends in major-flood occurrence across North America and Europe was approximately the number expected due to chance alone. Changes over time in the occurrence of major floods were dominated by multidecadal variability rather than by long-term trends. There were more than three times as many significant relationships between major-flood occurrence and the Atlantic Multidecadal Oscillation than significant long-term trends."

The paper is available from the Journal of Hydrology. The authors are from across the world.

Glenn A.HodgkinsaPaul H.WhitfieldbDonald H.BurncJamieHannaforddBenjaminRenardeKerstinStahlfAnne K.FleiggHenrikMadsenhLuisMedieroiJohannaKorhonenjConorMurphykDonnaWilsong

a

U.S. Geological Survey, 196 Whitten Road, Augusta, ME 04330, United States

b

Environment and Climate Change Canada, 401 Burrard Street, Vancouver, BC V6C 3S5, Canada

c

University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada

d

Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Wallingford, Oxfordshire OX10 8BB, United Kingdom

e

Irstea Lyon, Hydrology-Hydraulics, 5 rue de la Doua BP32108, 69616 Villeurbanne cedex, France

f

Albert-Ludwigs-Universität Freiburg, Fahnenbergplatz, 79098 Freiburg, Germany

g

Norwegian Water Resources and Energy Directorate, P.O. Box 5091, Majorstua, 0301 Oslo, Norway

h

DHI, Agern Allé 5, DK-2970 Hørsholm, Denmark

i

Technical University of Madrid, ETSI Caminos, Canales y Puertos, c/ Profesor Aranguren, 3 28040 Madrid, Spain

j

Finnish Environment Institute, SYKE, Freshwater Centre, P.O. Box 140, 00251 Helsinki, Finland

k

Irish Climate Analysis and Research UnitS (ICARUS), Department of Geography, Maynooth University, Maynooth, Co. Kildare, Ireland

Since rainfall intensities are not increasing dramatically across Canada, as demonstrated by Environment and Climate Change Canada (ECCC) in the Atmosphere-Ocean in 2014, saying rainfall intensities are stationary, it makes sense that major floods are not increasing either. Of course there may be local regional trends - ECCC found that there are decreasing rainfall intensities in regions such as the St Lawrence basin of southern Quebec and the Maritimes. Their Engineering Climate Datasets (version 2.3) also show twice as many statistically significant decreasing trends as increasing ones in southern Ontario.

The paper Climate-driven variability in the occurrence of major floods across North America and Europe focused on minimally altered catchments in order to isolate climatic as opposed to hydrologic drivers. It focused on large watersheds. As noted on this blog, urbanization is a key driver of flood risk in small urban catchments and is expected to have increased of the past  50-100 years in many Ontario cities. This is link to GIS mapping of changes: Ontario city urbanization affecting runoff and flood risk since from 1966 to 2000.