Abstract:

This study investigated the response of soil moisture content to precipitation events in Chongqing from April to October 2023 using hourly monitoring data on precipitation and soil relative humidity. Focusing on typical farmland clay loam, variations in soil relative humidity (0−50cm) were analyzed by Random forest regression and simple linear regression methods under diverse precipitation types, intensities and initial soil moisture conditions. The research aimed to elucidate soil moisture dynamics under natural precipitation and provide technical support for soil moisture forecasting and agricultural drought early warning. The results showed that: (1) increasing precipitation amounts significantly enhanced soil moisture content variation and recharged at 40−50cm depths. Light rain events only affected the 0−20cm layer, whereas moderate to heavy precipitation events activate soil moisture content response down to 20−50cm. During the torrential events, the 40−50cm soil moisture increment reached 5.92 percentage points (pp) compared to the pre−event baseline. (2) Higher precipitation intensity improved infiltration efficiency. Under grade IV intensity events, the 40−50cm soil moisture lag time (0.76h) and recharge rate (2.29pp·h⁻¹) showed shorter and higher versus Grade I events (lag time: 2.9h; recharge rate: 0.1pp·h⁻¹). (3) Under drought conditions (initial relative humidity<60%), the 0−10cm response intensity per unit precipitation (0.38pp·mm⁻¹) was 2.4 times higher than the 40−50cm layer (0.16pp·mm⁻¹). Moderate to heavy precipitation events (10−50mm) with Grades II−III intensity (5−15mm·h⁻¹) increased the plow layer (0−20cm) relative humidity by 10−30pp, significantly alleviating drought. Under optimal moisture (relative humidity≥60%), soil moisture increments decreased by approximately 50pp across all layers versus drought conditions.

Key words: Soil moisture, Precipitation, Response characteristics, Clay loam