How Does Soil Moisture Response to Precipitation Along a Typical Mixed Land-Use Hillslope in Taihu Lake Basin, China?.

A typical mixed land-use hillslope in Taihu Lake Basin was selected to investigate the characteristics and controlling factors of soil moisture (θ) response to precipitation (P). Along this hillslope, automatic soil moisture monitoring systems were installed at top slope, upper slope, middle slope, lower slope and toe slope positions, which corresponds to forest, tea plantation, tea plantation, meadow and forest land uses, respectively. Soil moisture at 0.1-, 0.2-, 0.4-, 0.6- and 0.65-m depths was collected at these five sites with 10-min interval. For each rainfall event, the initial θ, maximum θ and delta θ (maximum-initial) were picked out for each depth at study site. The following results were observed. First, both P amount and intensity influenced the degree of θ response to P. Delta θ was significantly (P<0.05) influenced by both P amount and intensity except for the meadow site. For rainfall events with similar P amounts and initial θ but different P intensities (e.g., Aug 21, Oct 29 and Nov 9, 2012), greater P intensities resulted in θ of more depths response to P. Second, when initial θ was dry, it strongly influenced the degree of θ response to P. For rainfall events with similar P but different initial θ (e.g., July 13, Aug 2 and Aug 8, 2012), the one with dry initial θ (Aug 2, 2012) had greater delta θ for most depths and study sites. A significant (P<0.05) linear relationship between initial θ and delta θ can be observed under the dry initial condition. Third, subsurface lateral flow was more important than P in influencingθ in the lower slope meadow site and toe slope forest site. For rainfall events with similar P (e.g., July 13, Aug 2 and Aug 8, 2012), the one with wet initial θ (July 13 and Aug 8, 2012) had much greater delta θ at the depths of 0.6 and 0.65 m at these two sites. In addition, the delta total water storages at the top 0.7 m soil profile of these two sites were greater than the cumulative P amount. Both observations suggested that these two sites were where the subsurface lateral flow accumulated. Results of this study will be useful in designing sustainable soil and water conservation strategies for developing the hilly areas in Taihu Lake Basin.