The response of soil moisture to precipitation in the source region of the Yellow River

The source region of the Yellow River (SRYR), with its semi-humid to semi-arid climate, is crucial for understanding water resource dynamics. Precipitation is key for replenishing surface water and balancing the ecosystem's water cycle. However, the soil moisture response to precipitation across climate zones and soil layers remains poor understood due to limited long-term data. This study examines the response of soil moisture to precipitation at multiple time scales in the SRYR, using data from Maqu, Mado, Ngoring Lake sites, and the Maqu monitoring network (MMN), along with CN0.51 precipitation and GLEAM v3.8a soil moisture data. Results show that semi-humid area require more precipitation to trigger soil moisture responses compared to semi-arid area in the SRYR. Surface soil at Maqu, MMN, Ngoring Lake, and Mado sites require at least 8.6 mm, 8.4 mm, 5.2 mm, and 2.84 mm of precipitation, respectively, for effective replenishment. Significant responses to precipitation events were observed in soil layers at 40 cm and above in the semi-humid area, while at 20 cm and above in the semi-arid area. Precipitation volume is the primary factor influencing soil moisture, affecting both the increment and time lag to maximum moisture. Precipitation intensity and pre-rain moisture have no direct effect. In the central SRYR, accumulated precipitation has a greater impact. Root-zone soil moisture has a weaker correlation with precipitation compared to surface soil moisture but persists longer, responding for up to 10 days, while surface soil moisture responds more immediately but only lasts about 5 days.