Extreme precipitation events and the applicability of global climate models to the study of floods and droughts

The intensification of the hydrologic cycle that can be expected under enhanced levels of greenhouse gases is attributed to an increase in the frequency of heavy precipitation events. The grid points in an atmospheric global climate model that cover the Midwest USA, show an increase in the mean and variability of daily precipitation. The number of raindays-per-year decreases but the intensity of precipitation increases. The Palmer Drought Severity Index (PDSI) is used to determine whether the changes in rainfall regimes may lead to more floods or droughts. Application of the PDSI, using precipitation and temperature from a ten-year equilibrated simulation for a typical grid paint in Midwest USA, shows that instances of wet and dry spells occur more frequently under enhanced greenhouse conditions.