Response of tropical precipitation to global warming

Abstract

Using high-resolution cloud-resolving simulations with different CO2 concentrations, local precipitation fluxes are found to obey Clausius-Clapeyron (CC) scaling. Previous studies of the effect of CO2 concentration on precipitation extremes have used general circulation models, which are poor platforms for studying tropical convection because convection is parameterized. In idealized cloud-resolving simulations, it is possible to identify not only the changes in local precipitation fluxes, but also the factors responsible for those changes. There are many properties of convection that can change as the atmosphere warms, each of which could produce deviations from CC scaling. These properties include the effective watervapor gradient, cloud pressure depth, and cloud velocity. A simple theory is developed that predicts the changes in these properties consistent with CC scaling. Convection in the cloudresolving simulations is found to change as predicted by this theory, leading to an ~20% increase in local precipitation fluxes when the CO2 concentration is doubled. Overall, an increase in CO2 leads to more vigorous convection, composed of clouds that are wider, taller, and faster. © 2011 American Meteorological Society.