Soil Water Response to Rainfall in Loess Plateau Forests: Insights From Water Transport and Recharge Processes

In China's Loess Plateau, soil water response to rainfall critically influences soil water content and distribution. Investigating these processes helps accurately evaluate soil infiltration and water retention capacities following vegetation restoration. This study examined three typical forest types (Robinia pseudoacacia plantation, Pinus tabuliformis plantation, and natural secondary forest) using high-frequency, fixed-point soil moisture monitoring to analyse soil water transport and recharge following 31 rainfall events. Results indicated that across all monitored rainfall events, the average throughfall for the Robinia pseudoacacia plantation, Pinus tabuliformis plantation, and natural secondary forest was 7.51, 5.62, and 5.32 mm, respectively. Light rainfall events dominated the annual rainfall. Under these rainfall conditions, the soil water in 0–40 cm soil layers was able to respond to rainfall, while soil below 40 cm depth couldnot receive immediate rainfall recharge. Soil water responded to rainfall predominantly through preferential flow mechanisms, with the occurrence frequency of preferential flow decreasing as soil depth increased, transitioning from preferential flow to matrix flow. Soil water transport rate, water recharge rate, and recharge volume all diminished significantly with soil depth. Compared to soil properties, the transport and recharge of soil water were more significantly influenced by rainfall conditions. Soil saturated hydraulic conductivity, porosity, and bulk density significantly controlled water transport and recharge, while soil texture and organic matter influenced the process primarily through effects on soil porosity. In the Loess Plateau region, vegetation restoration effectively enhances water conservation functions, while low-density afforestation demonstrates superior performance in promoting infiltration and water retention capabilities.