西南干热河谷土壤水分对降雨入渗的响应机制

Mechanisms of soil moisture response to rainfall infiltration in dry-hot valley of southwest China

以四川凉山州西昌喜德县热水河流域为研究区,在林地和草地样点5个土壤深度(10、20、50、75和100 cm)安装土壤水分传感器,连续采集10个月30 min分辨率土壤水分动态变化数据,解析土壤水分对降雨入渗的响应规律。研究表明:土壤水分对降雨入渗的响应特征在不同植被覆盖、降雨属性以及初始土壤水分条件下存在显著差异(P<0.05)。林地土壤水分响应降雨的雨量阈值为1.88 mm,而草地为9.15 mm。林地降雨入渗过程受降雨属性影响较小,下渗深度更深(浸润深度达到100 cm的事件超过76.08%,比草地多8.23%),表明增加林地植被覆盖能够更有效地促进深层土壤水分的补给和储存,进而减少水土流失。此外,雨量大、雨强高的降雨事件促进降雨下渗和深层土壤水分补给(草地小降雨和大降雨事件导致平均相对最大土壤水分增率分别为2.68%和71.16%)。初始土壤水分较高条件下,土壤水分对降雨输入的响应更快,但下渗深度相对较浅。上述结果反映了下垫面条件、降雨特征和初始土壤水分条件对降雨入渗过程的耦合调控机制,加深了对干热河谷土壤水分动态变化及降雨入渗机制的理解,反映出西南干热河谷水土保持治理中需要充分考虑当地降雨特征和初始土壤水分条件,且提高植被覆盖度可能是一种有效措施。

The dry-hot valley regions in southwest China have suffered serious soil erosion.Therefore,improving our understanding of soil moisture response to rainfall under different vegetation types in these regions can provide valuable insights into rainfall infiltration and redistribution patterns on hillslopes,which is of vital importance for soil erosion management.This study investigated these processes in the dry-hot valley of the Reshuihe River catchment in Sichuan Province.Soil moisture was monitored continuously at 30-minute intervals at five depths(10,20,50,75,and 100 cm)under woodland and grassland surfaces over 10 months.Rainfall events were classified based on the K-means clustering algorithm and 8 soil properties(rainfall infiltration depth,lag time of soil moisture response to rainfall,cumulative rainfall required for the response,relative maximum soil moisture increment,and relative maximum water storage increment)used to characterize the soil moisture response to rainfall.The results showed that rainfall infiltration is jointly controlled by rainfall properties,vegetation covers,and initial soil moisture conditions.The threshold value of rainfall amount for soil moisture response was 1.88 mm under woodland,while it increased to 9.15 mm under grassland.Soil moisture in woodland responded more readily and allowed greater infiltration depths with less influence from rainfall properties than that in grassland,which suggested that rainfall is more effectively absorbed and replenished deep soil moisture in woodland.Moreover,rainfall events with higher intensities promoted deeper percolation and more profound replenishment of soil moisture within the deeper layers of the soil.In conditions where the initial soil was wetter,soil moisture more swiftly responded to rainfall.These findings highlighted the complex interplay of vegetation covers,rainfall characteristics,and initial soil moisture conditions in the rainfall infiltration process,and deepened our understanding of soil moisture dynamics and rainfall infiltration mechanisms in the dry-hot valley.Firstly,these findings underscored the vital role of vegetation covers in mitigating soil erosion and managing water resources.The differences in rainfall thresholds for soil moisture response between woodland and grassland suggested that woodland can significantly enhance the ability to capture and retain rainfall in the landscape.These were particularly crucial in regions with a high risk of soil erosion,especially in the dry-hot valley.Additionally,the study emphasized the importance of rainfall properties,such as the rainfall intensity and the rainfall amount,as they significantly impacted on the depth and the recharge of soil moisture. Recognizing how rainfall properties affect soil moisture dynamics can inform more precise water management strategies and help optimize water resources utilization in dry-hot valleys. Furthermore, understanding the processes of soil moisture response to rainfall and their cotrolling factors can aid in developing more effective irrigation strategies and groundwater management practices, especially in areas with limited water resources. Such insights provided a solid scientific foundation for guiding soil and water conservation efforts in these regions.