How do regional distributions of daily precipitation change under warming?

Abstract

Global warming is changing the intensity distribution of daily precipitation, with an increased frequency of heavy precipitation and reduced frequency of light/moderate precipitation in GCM (General Circulation Model) projections. Projected future CMIP5 GCM changes in regional daily precipitation distribution can be described by a combination of two idealised modes: a frequency decrease mode, representing a reduction in the frequency of precipitation at all rain-rates; and a frequency shift mode, where the distribution shifts towards heavier rain-rates. A decrease in daily precipitation frequency and increase in intensity are projected in most regions, but the magnitude of change shows large regional variations. The two modes generally capture the projected shift from light/moderate to heavy rain-rates but do not recreate GCM changes at the very highest and lowest rain-rates. We propose a simple framework for deep convective precipitation change based on the DSE budget, which provides a physical explanation of these idealised modes in regions/seasons where deep convection dominates precipitation. One possibility is that a frequency decrease mode is driven by increased convective inhibition (CIN). In this DSE framework, increased moisture under warming could influence the shape of the precipitation intensity distribution, particularly at the highest rain-rates, but does not govern the overall magnitude of the shift to heavier rain-rates, which is not well described by the Clausius-Clapeyron relationship. Changes in daily regional precipitation are not free to respond only to local changes (in e.g. moisture) but are constrained by the DSE budget, particularly by DSE transport associated with the large-scale circulation.