Dynamic coupling between soil properties and water content in shrink-swell soils: Effects on surface hydrologic partitioning

The parameterization of soil hydraulic properties (i.e., porosity and hydraulic conductivity) remains an important source of uncertainty in land-surface and large scale hydrological models, especially for shrinkswell soils, whose soil properties continuously change over time. Much research in shrink-swell soils has been devoted to understanding the relation between soil type, water content, shrinking and cracking, and water retention and hydraulic conductivity curves as well as developing suitable vadose zone hydrological models to estimate the impact on water flow and contaminant transport. However, little is known about the feedback of the shrinking and cracking on surface hydrology and its potential effects on agricultural production and land-atmosphere interactions. Here, using a probabilistic theoretical model linking shrink-swell properties to the soil moisture dynamics at soil matrix to pedon scales, we analyze the two-way interaction between shrinking/cracking status and soil moisture and analyze the impact of shrinking on hydrologic fluxes (i.e., evapotranspiration, percolation). Relying on data from Ships clay soils in Texas, the analysis of the probability density function of soil moisture for various shrink-swell properties and rainfall regimes reveals that shrinking overall contributes to lowering the pedon-scale soil moisture and prolonging the persistence of dry soil moisture states. This persistence of dry states is also associated with a shorter memory timescale in shrink-swell soils. Our results shed light on the impact of shrinking on surface hydrology and, given the expected climate change, calls for more research focusing on land-atmosphere interactions and the potential effects on the persistence of droughts.