3.1 Rainfall characteristics and soil moisture dynamics
During the study period from May 1 to October 31, the precipitation instrument recorded 1-h rainfall and accumulated rainfall. The total rainfall reached 565.3 mm, accounting for 94.5% of the annual rainfall amount in 2019. A total of 13 rainfall events are described in Fig. 2f and Table 2, including the total amount, duration, and intensity, which were divided into four groups. Group I (P1 and P3) represented the heavy rainfall that was characterized by a relatively large amount and high peak intensity of rainfall. Group II (P2 and P4) represented intermediate rains with a short duration and high average intensity. Group III (P5, P6, P7, P12, and P13) represented light rains characterized by a short duration and low peak intensity. Group IV (P8, P9, P10, and P11) represented continuous rains with a long duration and a low intensity (Table 2).
Fig. 2 shows that the SM was positively correlated with rainfall input but fluctuated in different levels of different soil layers after precipitation. The results indicated that distinct cycles of wetting and drying in response to rainfall were evident in the shallow soil layer (10 and 30 cm soil depths). However, the deeper layers (70 and 100 cm soil depths) showed a gentle fluctuation range, which was confined in response to rainfall (Fig. 2).