Multi-depth evolution characteristics of soil moisture over the Tibetan Plateau in the past 70 years using reanalysis products

Abstract

Soil moisture (SM) is a crucial component of the hydrological cycle. Both the spatial–temporal distribution and the variation characteristics of SM are effective indicators of regional land surface water resource homogeneity and heterogeneity. With consideration of the crucial role of the Tibetan Plateau (TP) in the hydrological process in Asia, this study investigated the fluctuation of multi-depth soil moisture across the TP during 1950–2020 on a monthly scale against the background of global warming by using ERA5 reanalysis datasets. The correlation and potential causality between soil moisture and associated driving factors were explored. Our research revealed that the soil moisture across the TP shows a slight wetting trend at 0–100 cm depth for the past 70 years against the background of climate warming and increasing precipitation. Additionally, the wetting region (variation trend ≥ 0.005 m3/m3 per decade) had sufficient water supplementation from precipitation and a mild soil temperature increase. By comparison, there is a noteworthy warming tendency and falling precipitation in the sparsely distributed drying region (variation trend ≤ −0.005 m3/m3 per decade). In terms of vertical variation features, the temporal dynamic fluctuation of soil moisture and soil temperature evidently decreases as the depth increases, suggesting high sensitivity of the surface layer soil to atmospheric conditions. Precipitation and snowmelt preliminarily proved to be the dominant drivers causing spatial and temporal variations in soil moisture (occupying over 70% of the TP region), and bidirectional causality (ranging between 15.52% and 50.56%) was found between soil moisture and these two parameters. In summary, this study explored the spatial–temporal fluctuation in the evolutionary characteristics of SM, which is expected to advance our understanding of soil moisture dynamics under the conditions of climate change across the TP.