Construction And Application Of Hydrological Model Based On Spatial Distribution Of Runoff Generation Mechanism Under Changing Environment

Affected by climate change and large-scale human activities,the natural runoff in the middle reaches of the Yellow River has decreased significantly in the past half century.In order to explore the characteristics and causes of runoff changes in this area,supported by the "Thirteenth Five-Year" National Science and Technology Support Program "Water and Sediment Change Mechanism and Trend Forecast in the Yellow River Basin"(2016YFC040240203)and the National Natural Science Foundation of China(51979250),Gushanchuan basin and Tuweihe basin,the first-level tributaries in the middle reaches of the Yellow River,were selected as the research areas in this study.On the basis of the observed hydro-climatic data and water and soil conservation measures of the basins,the overall characteristics of the long-term runoff were analyzed.The trend test method was applied to detect the mutation period,combined with hydrological theories and modern statistical methods,the response law of flood characteristics and runoff generation mechanisms in different periods of typical river basins to changing environment was analyzed comprehensively.Based on the spatial distribution of the dominant runoff generation mechanism,we further construct a typical watershed distributed hydrological model,and different parameters were considered for the runoff generation calculation of the watershed from the mechanism level to verify the applicability of the model in the middle reaches of the Yellow River.The main results are as follows:(1)Based on GIS and trend mutation test and other mathematical statistical methods,the variation law of underlying surface conditions,precipitation,runoff and evaporation changes and their characteristics in the Gushanchuan basin and Tuweihe basin were investigated.From 1980 to 2010,the forest area of the Gushanchuan basin increased by 18.22 km2,and grassland area increased by 13.77 km2,mainly from cultivated land;the unused land in the Tuweihe basin decreased significantly,which increased the grassland area proportion from 38.65%to 57.09%,and the land use transformation of the underlying surface of the basin was significantly affected by human activities.Combining MK trend analysis and Pettitt mutation test,it is shown that the annual runoff in the two basins has a significant decreasing trend.The mutation years were 1997 and 1982,respectively,and the rainfall showed an insignificant upward and downward trend.(2)Five calculation frameworks based on Budyko theory were used to quantify the contribution rate of climate change and human activities to the reduction of runoff in the Gushanchuan and Tuweihe basin.Compared with the pre-mutation period,the runoff of the two basins was reduced by 77%and 36.6%,respectively.Climate change and human activities contributed 13.9%and 86.1%to the runoff change in Gushanchuan basin,respectively,and contributed 33.2%and 66.8%to the runoff change in the Tuweihe basin,respectively.Human activities are the dominant driving factors that cause runoff changes in the study area.(3)Integrating the rainfall-runoff correlation diagram and hydrological principles,based on the flow process line,the flood characteristics and the response law of runoff generation patterns under the changing environment of typical watersheds are analyzed.We found that the floods in the Gushanchuan basin were still dominated by Excessinfiltration runoff,but the proportion in 1965-1997 and 1998-2010 decreased gradually(68.46%and 45.83%in turn).The Tuweihe basin shows a similar phenomenon,the floods dominated by Excess-infiltration runoff accounted for 73.44%and 57.14%in 1956-1982 and 1983-2016,respectively.The spatial distribution map of runoff mechanism shows that the runoff generation type in the Gushanchuan basin has changed from Rs+Rint to Rint+Rsat,and the runoff generation type in Tuweihe Basin is Rs+Rint,showing that the Excess-infiltration runoff is still the dominant pattern.(4)Based on the results of spatial discrimination of dominant runoff generation mechanism,the principle of setting runoff generation parameters in sub-basin basins based on the spatial distribution of dominant runoff generation mechanism was proposed,and the HEC-HMS models of Gushanchuan and Tuweihe basins were constructed.Several floods with good relationship between rainfall and flood in the changing period are selected,and the parameters of the model are analyzed,and the simulation results are tested by using the model accuracy evaluation index.The results show that the simulation results are consistent with the observed data,the average Nash coefficients of the Gushanchuan and Tuweihe basins during the verification period are 0.77 and 0.83,respectively.The simulated forecast accuracy of the two basin models is both grade B.The HEC-HMS model based on the spatial distribution of the dominant runoff generation mechanism is suitable for the typical basins in the middle reaches of the Yellow River.