3.2 Soil moisture response depth to rainfall
Different rainfall patterns with different rainfall inputs significantly
impacted the soil moisture response depth across the five experimental
sites. Total amounts larger than 15.2 mm, 22.2 mm, and 114.2 mm could
trigger SM responses at depths of 10, 30, and 70 cm, respectively. For
example, heavy rains (Group I) infiltrated to a soil depth of at least
70 cm, while intermediate rains were limited at the 30 cm depth (Fig.
3). In addition, rainfall duration and intensity had a similar impact on
the soil wetting depth. When the rainfall duration was greater than 2.3
h, 13.0 h, and 22.0 h, the rainwater could percolate to soil depths
greater than 10, 30, and 70 cm, respectively. An average rainfall
intensity larger than 0.6 mm/h, 1.3 mm/h, and 6.2 mm/h could stimulate
SM responses at depths of 10, 30, and 70 cm, respectively (Fig. 3).
Land cover also strongly influenced the soil wetting depth after
precipitation. The average response depth was as follows: grass (57.5
cm) > forest (52.5 cm) > bare land (49.7 cm)
> shrub (46.2 cm) > crop (45.4 cm). After
converting crops to forests, shrubs, and grasses, the average soil
wetting depth increased by 15.7%, 1.7%, and 26.7%, respectively
(Supplemental Fig. S1). Two heavy rains (P1 and P3) are obvious, which
permitted rainwater to enter deeper soil in forest and grass sites than
in other sites (Fig. 3). In intermediate rains (P2 and P4), vegetation
recovery prevented rainfall infiltration, leading to a lighter SM
response or nonresponse after rainfall (Fig. 3a, c-e). However, the SM
of planted shrubs and bare land responded more deeply than that of the
other sites (Fig. 3b, e). For light rains and continuous rains, forest
and grass sites had deeper soil wetting depths in some specific response
processes, such as at P6 and P10.