A review of climate change impacts on design rainfalls

Abstract:

There is a wide variety of approaches to IDF (intensity-frequency-duration) rainfall projection in scientific literature: downscaling from climate change simulations, covariation with time, covariation with atmospheric variables, the use of historical climate proxies, and heuristic (theoretical) relationships. In practical flood guidance there is a dominance of downscaled climate simulation methods being used to develop factors for projecting peak rainfalls over a range of planning horizons.

All the methods and guidance reviewed point to an intensification of rainfall extremes with climate change, but the magnitude of the change differs with region. Despite evidence pointing to shorter duration rainfall extremes intensifying more than long duration extremes (and more extreme rainfalls more likely to see increases) not all guidance respects these differences. No methods factor the pattern of rainfall, that is, the spatial and temporal pattern of the rainfall, with the impact of changes in the spatial and temporal pattern of future flooding still highly uncertain. There is no guidance for changes in Probable Maximum Precipitation (PMP), a key input for many engineering designs.

We conclude that, overall, design flood guidance reflects the current science in terms of increasing rainfall intensities but often falls short of nuancing the change with respect to different exceedance probabilities and storm durations. Finally, more research is required on the impact of changes in temporal and spatial patterns of rainfall.