2.2.3 Soil moisture response to rainfall process
The SM response lag time (RT , h) was evaluated to characterize the temporal delay of the soil wetting process with depth. It is calculated as follows:
RT = STi - ST0 (1)
where STi and ST0represent the SM response time at layer i (layer1: 0-10 cm, layer2: 10-30 cm, layer3: 30-50 cm, layer4: 50-70 cm, layer5: 70-100 cm) and rainfall time, respectively. According to this case, we recorded the accumulated rainfall amount (ARA , mm) that could trigger SM increases in different soil layers:
ARA =\(\ \sum_{t=ST_{0}}^{\text{ST}_{i}}\text{\ R}\) (2)
where R represent the and real-time rainfall (mm), respectively.
Definition of the wetting front velocity (WFV , cm/h) at different soil depths used to describe the SM wetting dynamics after rainfall:
WFVij = SWDij / RTij (3)
where SWDij and RTij are the soil wetting depth (cm) and the response time (h) at layer i in the jth soil wetting process, respectively.