Deep soil water storage varies with vegetation type and rainfall amount in the Loess Plateau of China

Soil-water storage in a deep soil layer (SWSD), defined as the layer where soil water is not sensitive to daily evapotranspiration and regular rainfall events, functions as a soil reservoir in China's Loess Plateau (LP). We investigated spatial variations and factors that influence the SWSD in the 100-500 cm layers across the entire plateau. SWSD generally decreased from southeast to northwest following precipitation gradient, with a mean value of 587 mm. The spatial variation in the SWSD in grassland was the highest, followed by protection forests, production forests and cropland. Variation in the >550 mm rainfall zone was much lower than that in the <550 mm zone. The significant influencing variables explained 22.3-65.2% of the spatial variation in SWSD. The joint effect of local and climatic variables accounted for most of the explained spatial variation of SWSD for each vegetation type and the <450 mm rainfall zone. Spatial variation of SWSD, however, was dominantly controlled by the local variables in the 450-550 and the >550 mm rainfall zones. Therefore, regional models of SWSD for a specific vegetation need to incorporate climatic, soil and topographic variables, while for a rainfall zone, land use should not be ignored.