Does Soil Moisture Affect Warm Season Precipitation Over the Southern Great Plains?

Joshua Welty and Xubin Zeng

Department of Hydrology and Atmospheric Sciences

The University of Arizona

Numerous observational and modeling studies have addressed the impact of soil moisture on subsequent precipitation (primarily its initiation), yet consensus remains elusive. Here we quantify the effect of soil moisture on precipitation amplification over the U.S. Southern Great Plains, long considered as one of the global "hot spots" of land-atmosphere interaction, though more recent studies have questioned this designation. Warm season (June-September) days for the 2002-2011 period (with ~1220 total days) are partitioned into low, medium, and high dynamic regimes, among which certain days are identified as afternoon rainfall event days based on simple criteria. We find that antecedent soil moisture conditions are negatively correlated with subsequent afternoon precipitation magnitude for low dynamic regimes, but this correlation becomes positive for high dynamic regimes. In contrast, this correlation is markedly reduced in magnitude and becomes insignificant when all regime days are considered. These results are also confirmed by simple statistics and examination of the diurnal cycle. Furthermore, different pathways are provided for precipitation amplification for low and high dynamic regimes.