Assessment of Future Changes in Intensity-Duration-Frequency Curves for Southern Ontario using North American (NA)-CORDEX Models with Nonstationary Methods

TL;DR

This study evaluates how climate change may alter extreme rainfall patterns in Southern Ontario by comparing stationary and nonstationary models using regional climate model data, revealing increased intensities for certain events but no significant differences for others.

Contribution

It provides a comprehensive regional comparison of IDF statistics under future climate scenarios using multi-model RCM simulations and nonstationary extreme value analysis.

Findings

Future 10-year extreme rainfall intensities increase significantly in 2050s.

No significant difference between stationary and nonstationary IDF estimates for larger return periods.

Results suggest the need for updating design standards considering climate change impacts.

Abstract

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.