Climate Change and Rainfall Intensity–Duration–Frequency Curves: Overview of Science and Guidelines for Adaptation

One of the most important impacts of a future warmer climate is the projected increase in the frequency and intensity of extreme events. This increasing trend in extreme rainfall is seen in both the observational record and climate model projections. However, a review of the recent scientific literature paints a complex picture in which the intensification of rainfall extremes depends on a of factors. While some projected rainfall indices follow the Clausius-Clapeyron relationship scaling of an ∼7% increase in per 1°C of warming, there is substantial evidence that this scaling depends on rainfall extremes frequency, with longer return events seeing larger increases, leading to super Clausius-Clapeyron scaling in some cases. The intensification of extreme rainfall is now well documented at the daily scale but is less clear at the subdaily scale. In recent years, climate model simulations at a finer and temporal resolution, including convection-permitting models, have provided more reliable projections of subdaily rainfall. analyses indicate that rainfall scaling may also increase as a function of duration, such that shorter-duration, longer return period will likely see the largest rainfall increases in a warmer climate. This has broad implications on the design and the use of rainfall –duration–frequency (IDF) curves, for which both an overall increase in magnitude and a steepening can now be predicted. This also presents an overview of measures that have been adopted by various governing bodies to adapt IDF curves to the changing. Current measures vary from multiplying historical design rainfall by a simple constant percentage to modulating correction factors on return periods and to scaling them to the Clausius-Clapeyron relationship based on projected temperature increases. All of these measures fail to recognize a possible super Clausius-Clapeyron scaling of extreme rainfall and, perhaps more importantly, the scaling toward shorter-duration rainfall and the most extreme rainfall events that will significantly impact stormwater runoff in and in small rural catchments. This paper discusses the remaining scientific gaps and offers technical recommendations for practi- on how to adapt IDF curves to improve climate resilience