An Observational Radiative Constraint on Hydrologic Cycle Intensification

Hydrologic cycle intensification is a key dimension of climate change, with significant impacts on human and natural systems. A basic measure of hydrologic cycle intensification, the increase in global-mean precipitation per unit surface warming, varies by a factor of three in current-generation climate models (~1-3 % K-1). We show that a substantial portion of this spread can be traced to intermodel variations in the atmospheric shortwave absorption response to greenhouse-gas-induced warming. As climate warms, increases in shortwave absorption suppress the precipitation increase by reducing the latent heating required to balance the atmospheric energy budget. Spread in the shortwave absorption response can be explained by differences in the sensitivity of solar absorption to variations in column precipitable water. An observational estimate suggests that in many models, this sensitivity is too small, and that the shortwave absorption response to warming is too weak. Spread in the simulated sensitivity of solar absorption to varying water vapor concentration is linked to differences in radiative transfer parameterizations. Attaining accurate shortwave absorption responses through radiative transfer scheme improvement could reduce spread in global precipitation increase per unit warming at the end of the 21st century by ~35%, and produce an ensemble-mean increase that is almost 40% smaller.