Unraveling the dynamics of soil drought and its controlling factors across diverse ecosystems

Soil drought exhibits diverse characteristics across ecosystems due to intricate interactions within the soil–plant-atmosphere continuum. However, the dynamic variability and dominant factors of soil drought in different ecosystems remain unclear. To address this knowledge gap, this study characterized soil drought according to the standardized soil moisture index (SSMI) constructed using root-soil moisture data of the Global Land Data Assimilation System. Environmental factors were classified into three categories, namely climate factors (precipitation, temperature, and potential evapotranspiration), vegetation factors (NDVI and LAI), and topographic and soil factors (elevation, slope, aspect, groundwater storage, and soil texture). On this basis, the impact of terrestrial and meteorological multi-factors and their interactive effects on soil drought variation were examined through correlation analysis. Moreover, redundancy analysis (RDA) was employed to quantify the contribution of multiple drivers to soil drought in ecosystems, as well as identify the dominant factor. The results indicated that: (i) large-scale extreme drought events are more likely to occur in forest ecosystems than in farmland and grassland ecosystems; (ii) the duration of soil drought was longer in winter, especially in forest ecosystems; (iii) in winter, soil drought is more likely to occur in farmland ecosystems than in natural ecosystems; (iv) in farmland, grassland, and forest ecosystems, environmental factors explained 71.9%, 74.0%, and 77.8% of the changes in soil drought, respectively; (v) the dominant factor controlling soil drought was temperature for farmland ecosystems (F=321.20, p<0.01), and vegetation for forest (F=212.36, p<0.01) and grassland ecosystems (F=168.00, p<0.01).