Sensitivity of the Warm Rain Process in Convective Clouds to Regional Climate Change in the Contiguous U.S.

The hypothesis of an increase of the warm rain process within deep convective clouds under anthropogenic climate change is tested. A 1D warm rain microphysical model that represents the core of the clouds is run with past and future thermodynamic profiles derived from a global climate model and local aerosol estimates. The depth from the cloud base to the freezing level increases substantially in the future clouds. However, an arid environment, a faster updraft speed, or higher amounts of cloud condensation nuclei (CCN) can offset this effect, diminishing or preventing the expected increase in warm rain formation. The future clouds in some regions also exhibit a decreased sensitivity to CCN. These experiments illustrate that a universal assumption of a more active warm rain process in a warmer future climate is inappropriate. Future precipitation enhancement is likely to occur in regions where the warm rain process is currently marginally productive.