Abstract:
Soil moisture (SM) is a critical variable in terrestrial ecosystems, especially in arid and semi-arid areas where water sources are limited. Despite its importance, understanding the spatiotemporal variations and influencing factors of SM in these areas remains insufficient. This study investigated the spatiotemporal variations and influencing factors of SM in arid and semi-arid areas of China by utilizing the extended triple collation (ETC), Mann-Kendall test, Theil-Sen estimator, ridge regression analysis, and other relevant methods. The following findings were obtained: (1) at the pixel scale, the long-term monthly SM data from the European Space Agency Climate Change Initiative (ESA CCI) exhibited the highest correlation coefficient of 0.794 and the lowest root mean square error (RMSE) of 0.014 m3/m3; (2) from 2000 to 2022, the study area experienced significant increase in annual average SM, with a rate of 0.408×10–3 m3/(m3•a). Moreover, higher altitudes showed a notable upward trend, with SM increasing rates at 0.210×10–3 m³/(m3•a) between 1000 and 2000 m, 0.530×10–3 m3/(m3•a) between 2000 and 4000 m, and 0.760×10–3 m3/(m3•a) at altitudes above 4000 m; (3) land surface temperature (LST), root zone soil moisture (RSM) (10–40 cm depth), and normalized difference vegetation index (NDVI) were identified as the primary factors influencing annual average SM, which accounted for 34.37%, 24.16%, and 22.64% relative contributions, respectively; and (4) absolute contribution of LST was more significant in subareas at higher altitudes, with average absolute contributions of 0.800×10–3 m3/(m3•a) between 2000 and 4000 m and 0.500×10–2 m3/(m3•a) above 4000 m. This study reveals the spatiotemporal variations and main influencing factors of SM in Chinese arid and semi-arid areas, highlighting the more pronounced absolute contribution of LST to SM in high-altitude areas, providing valuable insights for ecological research and water resource management in these areas.
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