Investigating Relationship Between Soil Moisture and Precipitation Globally Using Remote Sensing Observations

The complex relationship between precipitation and soil moisture plays a critical role in land surface hydrology. Traditionally, the analysis of this relationship is restricted by the spatial coverage of both soil moisture and precipitation data that are collected through in-situ observations at limited locations. In this study, we utilized the National Aeronautics and Space Administration (NASA)'s remote sensing products of soil moisture (SMAP: Soil Moisture Active Passive) and precipitation (TRMM: Tropical Rainfall Measuring Mission), which provide near-global coverage, to investigate the co-variation of precipitation and soil moisture regionally, as a function of ecosystem types and climate regimes. We apply information on land cover and climate regimes to provide insight about correlation strength of soil moisture and precipitation. The results indicate that most of the globe has a moderate to strong positive correlation of SMAP soil moisture and TRMM precipitation data during the study period. In relation to land cover, soil moisture and precipitation have the strongest correlations in regions of limited vegetation, whereas forests and densely vegetated regions have weaker correlations. As for climate regimes, they have the strongest correlations in arid or cold regions, and weaker correlations in humid, temperate locations. While remotely sensed soil moisture data are less reliable in dense vegetation, these results confirm that drier, less vegetated climates show a highly linear relationship between soil moisture and rainfall.