黄土丘陵沟壑区坡沟系统不同降雨类型的土壤入渗特征

Rainfall⁃infiltration process and characteristics of slope⁃gully system in the hilly and gully region of the Loess Plateau

黄土高原退耕还林草生态建设改变了区域覆被格局和下垫面环境条件,对流域地表水文过程产生了重要影响。研究黄土丘陵沟壑区坡沟系统不同降雨类型下的土壤水分入渗特征,对揭示植被恢复驱动下的降雨⁃入渗机制变化具有重要的科学意义。基于坡沟系统土壤水分入渗过程的定位监测,阐明了坡沟系统土壤水分入渗特征对不同降雨类型的响应,并采用Horton、Mezencev、Kostiakov、USDA⁃NRCS模型进行土壤水分入渗过程模拟,筛选特定降雨类型下最佳的入渗模型。结果表明:(1)0—60 cm是降水—入渗过程响应的关键层次,沟坡总入渗蓄存量较坡面高约42.67%;(2)坡沟系统土壤水分入渗量与深度成反比,且沟坡土壤水分入渗量较坡面平均高约9.75%;(3)不同降雨类型下坡面湿润锋深度均小于沟坡,且以极端暴雨、长历时小雨强降雨最深,短历时中雨强次之,短历时小雨强降雨最浅;(4)坡沟系统各降雨类型土壤水分入渗量对降雨的响应表现出一定的滞后性,沟坡响应快于坡面,沟坡湿润锋深度平均较坡面深约5—10 cm;(5)Mezencev入渗模型对四种不同降雨类型入渗量的模拟均具有较高精度(Adj⁃R^(2)>0.96;NSE>0.92),Horton模型可用于模拟极端降雨类型(NSE>0.98),而Kostiakov模型、USDA-NRCS模型适于模拟短历时中强度降雨和短历时低强度降雨类型。

Since the implementation of a series of major ecological construction projects,vegetation has been restored on the Loess Plateau.Soil structure and physical characteristics changed by vegetation restoration,such as soil infiltration characteristics and soil water holding capacity and so on,have significant impacts on the surface hydrological process and mechanism of runoff generation and convergence.The change of environmental conditions in the underlying surface is necessarily change the surface hydrological process,the soil hydrological characteristics and mechanism of runoff generation and convergence on the Loess Plateau.The slope⁃gully system,as an important geomorphic unit of watershed on the Loess Plateau,is an integral part of the process of runoff generation and convergence and sediment transportation.Therefore,study of the rainfall⁃infiltration process is of great significance to comprehensively understand the rainfall⁃infiltration process of slope⁃gully system driven by“Grain for Green”projects on the Loess Plateau and reveal mechanism of runoff generation and convergence.In this paper,the dynamic response of different rainfall types and infiltration processes in the slope⁃gully system was studied by long⁃term dynamic monitoring of soil moisture in multiple depths.Based on clustering analysis,we divided the rainfall events into four different types.Afterward,the characteristics of soil moisture infiltration process under different rainfall types were analyzed.Results show that(1)soil moisture is sensitive to the response to rainfall events in the 0—60 cm soil layer,and the deepest level affected by the rainfall process is 60 cm.(2)The soil moisture infiltration amount of slope⁃gully system is inversely proportional to the depth,and the infiltration amount of downhill is about 9.75%higher than that of the uphill.(3)The depth of the wetting front is deeper with the extreme rainfall and long⁃duration light intensity type,followed by the short⁃duration medium intensity type,the shallowest by the short⁃duration light intensity type.(4)The response time of soil moisture under different rainfall types show different degrees of hysteresis,and there are significant differences.On the whole,the response of downhill is faster than that of uphill.Compare with the uphill,wetting front depth of downhill of each rainfall type is about 5—10 cm deeper than the uphill on average.(5)The Mezencev infiltration model has high accuracy in simulating the infiltration amount of four different rainfall types(Adj⁃R^(2)>0.96;NSE>0.92).The Horton model can be used to simulate extreme rainfall types(NSE>0.98),while the Kostiakov model and the USDA⁃NRCS model are suitable for simulating short duration medium intensity rainfall and short duration light intensity rainfall.