Anthropogenic intensification of short-duration rainfall extremes

Abstract

Short-duration (1–3\u2009h) rainfall extremes can cause serious damage to societies through rapidly developing (flash) flooding and are determined by complex, multifaceted processes that are altering as Earth’s climate warms. In this Review, we examine evidence from observational, theoretical and modelling studies for the intensification of these rainfall extremes, the drivers and the impact on flash flooding. Both short-duration and long-duration (>1\u2009day) rainfall extremes are intensifying with warming at a rate consistent with the increase in atmospheric moisture (~7%\u2009K−1), while in some regions, increases in short-duration extreme rainfall intensities are stronger than expected from moisture increases alone. These stronger local increases are related to feedbacks in convective clouds, but their exact role is uncertain because of the very small scales involved. Future extreme rainfall intensification is also modulated by changes to temperature stratification and large-scale atmospheric circulation. The latter remains a major source of uncertainty. Intensification of short-duration extremes has likely increased the incidence of flash flooding at local scales, and this can further compound with an increase in storm spatial footprint to considerably increase total event rainfall. These findings call for urgent climate change adaptation measures to manage increasing flood risks. Short-duration rainfall extremes are determined by complex processes that are affected by the warming climate. This Review assesses the evidence for the intensification of short-duration rainfall extremes, the associated drivers and the implications for flood risks. Heavy rainfall extremes are intensifying with warming at a rate generally consistent with the increase in atmospheric moisture, for accumulation periods from hours to days. In some regions, high-resolution modelling, observed trends and observed temperature dependencies indicate stronger increases in short-duration, sub-daily, extreme rainfall intensities, up to twice what would be expected from atmospheric moisture increases alone. Stronger local increases in short-duration extreme rainfall intensities are related to convective cloud feedbacks, but their relevance to climate change is uncertain, owing to modulation by changes to temperature stratification and large-scale atmospheric circulation. It is unclear whether storm size will increase or decrease with warming; however, increases in rainfall intensity and the spatial footprint of a storm can compound to substantially increase the total rainfall during an event. Evidence is emerging that sub-daily rainfall intensification is related to an intensification of flash flooding, at least locally. This intensification will have serious implications for flash flooding globally and requires urgent climate change adaptation measures. Heavy rainfall extremes are intensifying with warming at a rate generally consistent with the increase in atmospheric moisture, for accumulation periods from hours to days. In some regions, high-resolution modelling, observed trends and observed temperature dependencies indicate stronger increases in short-duration, sub-daily, extreme rainfall intensities, up to twice what would be expected from atmospheric moisture increases alone. Stronger local increases in short-duration extreme rainfall intensities are related to convective cloud feedbacks, but their relevance to climate change is uncertain, owing to modulation by changes to temperature stratification and large-scale atmospheric circulation. It is unclear whether storm size will increase or decrease with warming; however, increases in rainfall intensity and the spatial footprint of a storm can compound to substantially increase the total rainfall during an event. Evidence is emerging that sub-daily rainfall intensification is related to an intensification of flash flooding, at least locally. This intensification will have serious implications for flash flooding globally and requires urgent climate change adaptation measures.