Dynamic response of soil water to rainfall for different runoff plots on a karst hillslope

Differences in land use on karst hillslopes inevitably lead to variations in the response of soil water to rainfall, resulting in differences in hydrology and erosion processes. Nevertheless, long-term and high-integrity in situ field monitoring data from runoff plots on karst slopes remain limited, therefore, the dynamic changes of soil water in response to rainfall under natural precipitation conditions are still unclear. This study was conducted to quantify the spatiotemporal dynamic changes in soil water for three different runoff plots (grassland, farmland, and bare land) on a karst hillslope. Soil water was measured across 0–100 cm profiles at 15 min intervals from June to December 2022. The results demonstrate that the average soil water content in the vertical profile was in the order of grassland > farmland > bare land. There was a soil water deficient layer in the vertical profile, such as grassland at 20 cm and 60 cm, farmland at 40 cm, and bare land at 20 cm. Light rainfall of 5.4 mm affected only the 0–20 cm surface layer of grassland, moderate rainfall of 20.8 mm influenced the 0–40 cm shallow soil water content. Notably, rainfall events exceeding 40.8 mm induced soil water dynamic responses throughout the entire 0–100 cm soil profile, and this phenomenon has important regional significance. In runoff plots, the temporal and spatial variations of soil water content across soil profiles are significantly affected by rainfall characteristics and land uses. For the entire soil profile, there was a significant correlation among the rainfall amount, rainfall duration, and increase in the soil water content. Moreover, the correlation coefficient between rainfall and the soil water content decreased with increasing soil depth. In both the less rainy period and the rainy period, the efficiency of soil water storage in each layer decreased in the following order: grassland > farmland > bare land. The differences in soil water storage for different karst runoff plots were controlled mainly by the amount of rainfall. It is suggested that grassland should be given priority for hillslope land use in humid karst areas, followed by farmland. The results contribute to a better understanding of the spatiotemporal distribution characteristics and influencing factors of soil water on karst hillslopes, providing theoretical references for the management of soil water resources, soil and water conservation, and the formulation of ecological restoration policies for rocky karst desertification areas.