Revisiting Soil Hydrology Across Scales - From Point to Remote Sensing Footprint Scale

With the growth of remote sensing platforms for measuring land surface attributes, it is imperative that we revisit our decades-long strategies to better understand soil hydrology and determine soil hydraulics at appropriate spatial scales. Land and sub-surface heterogeneity impacts soil hydrology in various ways. It changes drainage fluxes by altering soil structure, affects land-atmosphere interactions through evapotranspiration and alters soil infiltration by changing the rate and amount of rainfall reaching the soil surface. However, these effects manifest and become relevant at different scales of analysis. At the field and watershed scale, factors like landscape location, organic matter, landuse-landcover and soil bulk density cause non-equilibrium in soil water flow and hence impact drainage. This has implications for estimating solute transport from the near surface to groundwater, water use management for irrigation and ground water recharge potential. On the other hand, large scale soil hydrology dependent processes like climate change and land-surface interactions have shown to be highly correlated with remote sensing pixel scale soil moisture. Various factors that are important for field scale studies average out at this scale and yet unknown emergent properties govern soil hydrologic behavior at this scale. In this presentation, we will revisit and compare the performance of several of the traditional approaches and recently developed effective concepts related to soil hydrology under: (1) homogeneous and heterogeneous land surface conditions, (2) non-equilibrium flow through preferential flow paths, and (3) dynamic plant available water in the root zone. At the field and watershed scales, our results show that while landuse-landcover had a significant effect on the potential for preferential flow, landscape locations such as depressions that consistently caused soils to remain wet also had more differences in drainage fluxes between equilibrium and nonequilibrium models. At larger scales we propose a new heterogeneity index defined by Gaur and Mohanty, 2019 or variants thereof could be used in place of soil properties such as porosity to classify soil water dynamics beyond the REV scale. Results will be showcased at several watersheds and hydroclimates across USA.