Representing Spatial Subgrid-Scale Precipitation Variability in a GCM

A method for spatial disaggregation of rainfall to be used within a GCM is presented and the climate sensitivity to its parameters is assessed. The method is based on the assumption of exponential distribution of rainfall rates that are a function of the area of the GCM grid square where precipitation is occurring. When the method is applied in offline experiments, decreasing the fractional area where precipitation occurs decreases canopy interception, and, therefore, the partition of surface evaporation between leaf water evaporation and canopy transpiration. The climate, simulated using the precipitation disaggregation scheme, shows considerable changes from the simulated control climate with overall warmer and drier tropical land and warmer high-latitude continental areas. Changes in the simulated climate can be explained by direct local land-atmosphere interaction processes enhanced by regional atmospheric feedback mechanisms and remote responses to changes in tropical heating linked to differences in precipitation.