Using lagged dependence to identify (de)coupled surface andsubsurface soil moisture values

Abstract

Abstract. Recent advances in radar remote sensing popularized mapping of surface soil moisture at different spatial scales.Surface soil moisture measurements are used in combination with hydrological models to determine subsurface soil moisture values. However, variability of soil moisture across the soil column is important for estimating depth-integrated values as decoupling between surface and subsurface can occur. In this study, we employed new methods to investigate the occurrence of (de)coupling between surface and subsurface soil moisture. Lagged dependence was incorporated in assessing (de)coupling 5 with the idea that surface soil moisture conditions will be reflected at the subsurface after a certain delay. An exploratory step using residuals from a fitted loess function was performed as a posteriori information to determine (de)coupled values. The main approach was applying a distributed lag non-linear model (DLNM) to simultaneously represent both functional relation and lag structure. Both methods allow for a range of (de)coupled soil moisture values to be quantified. Results provide new insights on the decoupled range as its occurrence is not limited to dry conditions.