Soil Moisture Impacts on Afternoon Precipitation: A Regional Case Study with Global Extension

Many observational and modeling studies have examined the effects of antecedent soil moisture (SM) on afternoon precipitation (P), but consensus remains elusive. The question remains: does morning soil moisture affect afternoon precipitation over a “hot spot” region like the U.S. Southern Great Plains, and if so, how then does the SM-P relationship manifest globally? First we perform a regional analysis to quantify the relationship between morning soil moisture and afternoon precipitation amplification (with a focus on precipitation accumulation rather than initiation) over the Southern Great Plains under varying dynamic conditions (Welty and Zeng, 2018, Geophys. Res. Lett., doi: 10.1029/2018GL078598). Warm season (June-September) days for the 2002-2011 period (with ~1220 total days) are partitioned into three dynamic regimes based on daily water vapor convergence, among which afternoon precipitation event days are identified through simple criteria. We find that morning soil moisture and afternoon precipitation are negatively (positively) correlated under low (high) dynamic regimes. In contrast, the correlation is markedly reduced in magnitude and becomes insignificant when all afternoon precipitation event days are considered without dynamic regime partitioning. Under this framework, we then extend the analysis globally utilizing NASA Soil Moisture Active Passive (SMAP) soil moisture data to address the SM-P relationship conditioned on dynamic regimes. Regions of significant correlation between morning soil moisture and afternoon precipitation magnitude will be highlighted. In particular, we will explore if any other regions also exhibit conditionally opposing SM-P correlations under different dynamic conditions. Additional statistical analyses will be provided to further explore SM-P correlations over various regions.