Land-surface controls on near-surface soil moisture dynamics: Traversing remote sensing footprints

In this new era of remote-sensing based hydrology, a major unanswered question is how to incorporate the impact of land-surface based heterogeneity on soil moisture dynamics at remote sensing scales. The answer to this question is complicated since (1) soil moisture dynamics that vary with support, extent, and spacing scales are dependent on land-surface based heterogeneity and (2) land-surface based heterogeneity itself is scale-specific and varies with hydroclimates. Land-surface factors such as soil, vegetation, and topography affect soil moisture dynamics by redistributing the available soil moisture on the ground. In this study, we determined the contribution of these biophysical factors to redistribution of near-surface soil moisture across a range of remote sensing scales varying from an (airborne) remote sensor footprint (1.6 km) to a (satellite) footprint scale (25.6 km). Two-dimensional nondecimated wavelet transform was used to extract the support scale information from the spatial signals of the land-surface and soil moisture variables. The study was conducted in three hydroclimates: humid (Iowa), subhumid (Oklahoma), and semiarid (Arizona). The dominance of soil on soil moisture dynamics typically decreased from airborne to satellite footprint scales whereas the influence of topography and vegetation increased with increasing support scale for all three hydroclimates. The distinct effect of hydroclimate was identifiable in the soil attributes dominating the soil moisture dynamics. The near-surface soil moisture dynamics in Arizona (semiarid) can be attributed more to the clay content which is an effective limiting parameter for evaporation whereas in Oklahoma (humid), sand content (limiting parameter for drainage) was the dominant soil attribute. The findings from this study can provide a deeper understanding of the impact of heterogeneity on soil moisture dynamics and the potential improvement of hydrological models operating at footprints' scales.