The response of the hydrological cycle to climate change

Changes in the distribution of precipitation with global warming have many societal impacts and are not fully understood. We study two important changes in precipitation with global warming, namely the expected increase in the strength of precipitation extremes, and the expected decrease in mean precipitation in subtropical regions. We use a hierarchy of models, including a high resolution Cloud Resolving Model (CRM), an idealized General Circulation Model (GCM), and fully coupled GCMs from the archive for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).

Precipitation extremes are found to increase robustly in climate model simulations of global warming. There is also some observational evidence for large increases in precipitation extremes with atmospheric warming. The strength of precipitation extremes will be affected by thermodynamic changes in the saturation water vapor pressure, but changes in atmospheric dynamics also play a role through the updraft strength. Recent results suggest that climate models do not agree on the changes in updraft strengths associated with tropical precipitation extremes under global warming. We investigate this further by examining how updraft strength changes with warming in a high resolution cloud resolving model.

Unlike precipitation extremes under global warming, mean precipitation increases in some regions but decreases in others. Both mean precipitation and relative humidity are found to decrease near the subtropics in climate model simulations. Tropical precipitation is known to be strongly tied to the relative humidity distribution. We investigate whether changes in mean precipitation are related to changes in mean relative humidity, and how consistent this relationship is in climate models.