| The effects of human activities on the ecological environment in soil and water loss regions have become the focus of attention in academic field recently. Land use change is one of main reasons that could significantly affect the processes of runoff generation and concentration and sediment yield of watershed, and also is the main approach for human beings to intervene or disturb soil and water loss environment of watershed. According to the inter-disciplinary theories such as hydrology, sediment transport mechanics, soil and water conservation, ecology, etc, by using the integration of theoretical analysis and numerical simulation methods, together with taking typical watersheds on Loess Plateau as study objects, with the data of rainfall process and watershed underlying surface, the runoff generation and concentration processes for single rainstorm were inversed, and the effects of watershed land use change on the process of watershed runoff and sediment variation was analyzed in the paper. As a result, a watershed runoff and sediment yield model for single rainstorm event with considering land use dramatical change was proposed. According to the related data of land use change and the planning of soil and water conservation and eco-environmental construction, by using the distributed simulation method of watershed runoff and sediment, the future evolution tendency of soil and water loss environment on Loess Plateau was predicted in the paper. The main conclusions are as follows:(1) A runoff generation and concentration model composed of watershed runoff generation model and watershed routing model was established. In watershed runoff generation model, the calculation of runoff generation for single rainstorm with unsteady rainfall intensity, based on the method of infiltration capacity curve of Horton infiltration equation as well as the consideration of the initial runoff-yielding time, was carried out at each time interval. The Nash instantaneous unit hydrograph was used in watershed runoff routing model. A new calculation method used for numerical solution of S-curve value of time unit hydrograph with the advantages such as higher operation speed and higher calculation accuracy, i.e. the integration of five-node Gauss-Laguerre Quadrature Formula and Romberg Quadrature Formula, was proposed in the paper.(2) The inversion method of runoff generation process for single rainstorm on field slope runoff plots was proposed. By using the above calculation method of runoff generation for single rainstorm with unsteady rainfall intensity as well as optimization method of model parameters based on modified weighted centroid simplex method, the runoff generation process for single rainstorm on slope runoff plots of different land use types were inversed in the paper. The results of preliminary model validation indicated that the proposed inversion method had better calculation accuracy,thus it could be used for deep information mining from the abundant existing observed data of runoff for single rainstorm on slope runoff plots.(3) The concept of runoff erosion power for single rainstorm, which could be used for describing the erosion dynamics of soil erosion and sediment transport in the process of water erosion, and its calculationmethod based on two characteristic values of flood hydrograph, i.e. peak discharge modulus and runoff depth, were proposed. In addition, the correlations of runoff erosion power and watershed sediment transport modulus at different spatial scales including slope, slope-gully and watershed, were systematically analyzed, as a result, runoff-sediment response model for single rainstorm event based on runoff erosion power was established and validated. The results showed that the established model had high calculation accuracy, thus could be used for predicting sediment yield in single rainstorm of watershed at different scales and different soil and water conservation degrees. The roles of rainfall erosivity and runoff erosion power in the process of water erosion were compared with each other at slope and watershed scales, which results indicated that, compared with rainfall erosivity, because runoff erosion power could directly reflect the effects of rainfall and underlying surface factors on the process of water erosion and could closely show the dynamics mechanism of water erosion, it could describe more effectively and sensitively the erosion dynamic of water erosion and sediment yield characteristic for single rainstorm at slope and watershed scales.(4)Zhifangou watershed with long-term observed land use data was seceted as a case typical watershed. With the consideration of the different runoff-generating characteristics of different land use types, the watershed was divided into five land use units including farmland, woodland, grassland, orchard land, non-production land. According to the established watershed runoff generation and concentration model and runoff-sediment response model based on runoff erosion power, a watershed runoff and sediment yield prediction model with the consideration of land use dramatical change was established and preliminarily validated by using the historical observed data of runoff and sediment for single rainstorm event and the corresponding areas of land use types in Zhifanggou watershed. The results indicated that the established model has better accuracy.(5) The temporal-spatial distribution and evolution characteristics of main soil and water conservation measures includeing biological measures, terrace and check dam, on Loess Plateau were comprehensively analyzed in the paper. Based on the data of the planning of soil and water conservation and eco-environmental construction, by using the distributed simulation method of watershed runoff and sediment, together with taking the forty subwatershed on Loess Plateauas as a calculation unit respectively, the evolution tendencies of soil and water loss environment on Loess Plateau in the coming 2010, 2015, 2020, 2030 and 2050 year were predicted, and the corresponding thematic maps including vegetation coverage, runoff modulus and soil erosion modulus were mapped too. The results preliminarily revealed the environmental benenfits of large-scale soil and water conservation on Loess Plateau in the future.
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