Mechanisms of soil moisture response to rainfall infiltration in dry-hot valley of southwest China
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Abstract:
The dry-hot valley regions in southwest China have suffered serious soil erosion. Therefore, improving our understanding of soil moisture response to rainfall under different vegetation types in these regions can provide valuable insights into rainfall infiltration and redistribution patterns on hillslopes, which is of vital importance for soil erosion management.This study investigated these processes in the dry-hot valley of the Reshuihe River catchment in Sichuan Province. Soil moisture was monitored continuously at 30-minute intervals at five depths (10, 20, 50, 75, and 100 cm) under woodland and grassland surfaces over 10 months. Rainfall events were classified based on the K-means clustering algorithm and 8 soil properties (rainfall infiltration depth, lag time of soil moisture response to rainfall, cumulative rainfall required for the response, relative maximum soil moisture increment, and relative maximum water storage increment) used to characterize the soil moisture response to rainfall.The results showed that rainfall infiltration is jointly controlled by rainfall properties, vegetation covers, and initial soil moisture conditions. The threshold value of rainfall amount for soil moisture response was 1.88 mm under woodland, while it increased to 9.15 mm under grassland. Soil moisture in woodland responded more readily and allowed greater infiltration depths with less influence from rainfall properties than that in grassland, which suggested that rainfall is more effectively absorbed and replenished deep soil moisture in woodland. Moreover, rainfall events with higher intensities promoted deeper percolation and more profound replenishment of soil moisture within the deeper layers of the soil. In conditions where the initial soil was wetter, soil moisture more swiftly responded to rainfall.These findings highlighted the complex interplay of vegetation covers, rainfall characteristics, and initial soil moisture conditions in the rainfall infiltration process, and deepened our understanding of soil moisture dynamics and rainfall infiltration mechanisms in the dry-hot valley. Firstly, these findings underscored the vital role of vegetation covers in mitigating soil erosion and managing water resources. The differences in rainfall thresholds for soil moisture response between woodland and grassland suggested that woodland can significantly enhance the ability to capture and retain rainfall in the landscape. These were particularly crucial in regions with a high risk of soil erosion, especially in the dry-hot valley. Additionally, the study emphasized the importance of rainfall properties, such as the rainfall intensity and the rainfall amount, as they significantly impacted on the depth and the recharge of soil moisture. Recognizing how rainfall properties affect soil moisture dynamics can inform more precise water management strategies and help optimize water resources utilization in dry-hot valleys. Furthermore, understanding the processes of soil moisture response to rainfall and their cotrolling factors can aid in developing more effective irrigation strategies and groundwater management practices, especially in areas with limited water resources. Such insights provided a solid scientific foundation for guiding soil and water conservation efforts in these regions.
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