Abstract
Abstract. In Canada, risk of flooding due to heavy rainfall has risen in recent decades; the most notable recent examples include the July 2013 storm in the Greater Toronto region and the May 2017 flood of the Toronto Islands. We investigate nonstationarity and trends in the short-duration precipitation extremes in selected urbanized locations in Southern Ontario, Canada, and evaluate the potential of nonstationary intensity–duration–frequency (IDF) curves, which form an input to civil infrastructural design. Despite apparent signals of nonstationarity in precipitation extremes in all locations, the stationary vs. nonstationary models do not exhibit any significant differences in the design storm intensity, especially for short recurrence intervals (up to 10 years). The signatures of nonstationarity in rainfall extremes do not necessarily imply the use of nonstationary IDFs for design considerations. When comparing the proposed IDFs with current design standards, for return periods (10 years or less) typical for urban drainage design, current design standards require an update of up to 7 %, whereas for longer recurrence intervals (50–100 years), ideal for critical civil infrastructural design, updates ranging between ∼ 2 and 44 % are suggested. We further emphasize that the above findings need re-evaluation in the light of climate change projections since the intensity and frequency of extreme precipitation are expected to intensify due to global warming.
Highlights
Short-duration extreme rainfall events can have devastating consequences, damage to crops and infrastructures, leading to severe societal and economic losses in Canada (CCF, 2013; TRCA, 2013)
We find the presence of statistically significant autocorrelations in the annual maximum precipitation (AMP) time series of Toronto International Airport, Hamilton Airport, and Fergus Shand Dam
Comparison of at-site T −year event estimates of updated vs. ECgenerated IDFs shows at T = 10 years, the return period commonly used for urban drainage design, current design standards require updates of up to 7 % to mitigate the risk of urban flooding
Summary
Short-duration extreme rainfall events can have devastating consequences, damage to crops and infrastructures, leading to severe societal and economic losses in Canada (CCF, 2013; TRCA, 2013). The increased water-holding capacity of warmer air, as governed by the Clausius–Clapeyron (C–C) relation (Lenderink and van Meijgaard, 2008; O’Gorman and Schneider, 2009; Wasko and Sharma, 2015, 2017), intensifies heavy rainfall at a rate of approximately 7–8 % ◦C−1 of warming. For sub-hourly and up to 6-hourly extreme precipitation, increases at or above the C–C rate have been found in the Netherlands (Lenderink and van Meijgaard, 2008; Lenderink et al, 2017), Switzerland (Ban et al, 2014), Germany (Berg et al, 2013), the UK (Blenkinsop et al, 2015), the Mediterranean (Drobinski et al, 2016), most of Australia (Wasko and Sharma, 2015, 2017; Schroeer and Kirchengast, 2017), North America (Shaw et al, 2011), and China (Miao et al, 2016), while in India (Ali and Mishra, 2017) and northern Australia (Hardwick Jones et al, 2010) negative rates have been reported.
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