Principles of terrestrial water distribution patterns and the role of soil hydraulic properties

Terrestrial water, which plays an essential role in ecosystems, is unbalanced in terms of storage and distribution patterns under natural conditions. The formation mechanism of this imbalance is relevant to soil hydraulic properties (SHP), surface terrain, and meteorological factors. In this study, the features of high-precision hydrological models and their specific soil hydraulic parameters were useful in providing some important insights and an effective approach towards a better understanding of the mechanisms that affect the representative terrestrial hydrological variables. First, the Penn State Integrated Hydrologic Model (PIHM), a physically based, coupled surface–subsurface hydrological model was used to investigate the relationship between terrestrial water distribution patterns and external driving factors of the study area within Yunnan Province, China. Subsequently, a variance-based sensitivity analysis method was used to measure the effects of SHP on terrestrial hydrological variables and their variability under different driving factors, including rainfall intensity and surface topography. It was found that (a) the areas with lower elevations and plain terrain tend to retain more soil moisture, (b) generally, the porosity of soil is the primary determiner of soil moisture storage and groundwater depth among other hydraulic properties, and (c) the importance ranking of the SHP parameters changes according to precipitation, surface elevation, and slope.