  The evaluation of possible climate change consequence on extreme rainfall has
significant implications for the design of engineering structure and
socioeconomic resources development. While many studies have assessed the
impact of climate change on design rainfall using global and regional climate
model (RCM) predictions, to date, there has been no comprehensive comparison or
evaluation of intensity-duration-frequency (IDF) statistics at regional scale,
considering both stationary versus nonstationary models for the future climate.
To understand how extreme precipitation may respond to future IDF curves, we
used an ensemble of three RCMs participating in the North-American (NA)-CORDEX
domain over eight rainfall stations across Southern Ontario, one of the most
densely populated and major economic region in Canada. The IDF relationships
are derived from multi-model RCM simulations and compared with the
station-based observations. We modeled precipitation extremes, at different
durations using extreme value distributions considering parameters that are
either stationary or nonstationary, as a linear function of time. Our results
showed that extreme precipitation intensity driven by future climate forcing
shows a significant increase in intensity for 10-year events in 2050s
(2030-2070) relative to 1970-2010 baseline period across most of the locations.
However, for longer return periods, an opposite trend is noted. Surprisingly,
in term of design storms, no significant differences were found when comparing
stationary and nonstationary IDF estimation methods for the future (2050s) for
the larger return periods. The findings, which are specific to regional
precipitation extremes, suggest no immediate reason for alarm, but the need for
progressive updating of the design standards in light of global warming.
