Spatial-temporal variability pattern of multi-depth soil moisture jointly driven by climatic and human factors in China

Abstract

Soil moisture (SM), which plays a critical role in land–atmosphere hydrological cycles, acts as the dominant water resource for vegetation growth. In China, the spatial–temporal variation in multi-depth SM patterns caused by the combined influence of climatic and human factors remains unclear. In this study, we systematically investigated the trends of SM as well as the relationship between SM and the multiple factors affecting it. Our results indicated that variability in SM in China was quite unbalanced during the 1950–2020 period. Mainly, the region covering North China and central Northeastern China underwent significant drying and exhibited a remarkable warming trend. By contrast, the wetting region, characterized by decreasing soil temperature in the summer, was concentrated in the area encompassing the Kunlun and Tianshan Mountains. As the depth increased, the drought level in the drying region steadily intensified, while the dampness degree in the wetting region gradually shrank. Such a consistently intensifying SM deficit inevitably threatens crop yield and food security. Correlation and Granger causality analyses indicated that precipitation and evaporation may act as dominant climatic factors that drive the variability of multi-depth SM, this driving force gradually declining with increasing depth, due to buffering by upper soil layers. By contrast, the correlation between human water withdrawal and SM grew continuously with increasing depth, except when irrigation was involved, implying that deep layer SM is susceptible to water intake. These findings are expected to boost the understanding of patterns of SM in China and provide a reference for future exploration, usage, and management of SM as well.