Effects Of Rainstorm Characteristics And Land Use On Watershed Flood Process

Global population growth,climate warming and environmental degradation are becoming increasingly serious.The ecological environment and water cycle process of the basin have been damaged,and extreme rainstorm has led to frequent floods.Based on the hydrological hydrodynamic model,the impact of rainstorm characteristics and land use change on basin flood is studied,and the change rule of basin flood under different scenarios of rainstorm characteristics and land use change is discussed.It is of great significance to the prevention of flood disasters in the watershed,land use planning and the formulation of flood control measures in the watershed.In this paper,a two-dimensional hydrological hydrodynamic model is used to simulate and analyze the process simulation of flood response in the Hulu River basin under the characteristics of rainstorm and land use change.By simulating the flood routing process and relevant hydrodynamic factors under different rainstorm characteristics or land use alone.Further simulate the response results of basin flood under the combined action of rainstorm characteristics and land use,and discuss the change rules of flood peak discharge and peak water depth.Predict the basin flood process under the scenarios of future rainstorm and land use change,quantify the changes of peak flow and peak water depth under different scenarios in the future.To provide scientific and technological support for future flood prevention,reduction,and disaster relief in the watershed.The main research content and achievements are as follows:(1)Based on meteorological data from 1960 to 2020 and land use data from 1985 to 2020 in the Hulu River Basin,statistical analysis is conducted on the characteristics of rainfall and land use change.The results show that the precipitation in the Huluhe River Basin showed an insignificant decreasing trend from 1960 to 2020,with uneven spatial distri bution of rainfall,gradually decreasing from southeast to northwest;the number of rainstorm days and annual rainstorm increase year by year;the spatial distribution of rainstorm days gradually decreases from southeast to northwest;the rainstorm volume in the southeast and northwest regions is large,and the rainstorm volume in the northeast and southwest regions is small.It shows that rainstorm is easy to occur in the southeast area of Huluhe River basin,and the rainstorm volume is large.The main types of land use in the Hulu River Basin are arable land and grassland.Between 1985 and 2020,cultivated land showed a trend of first increasing and then decreasing,while grasslands,water bodies,and unused land showed a trend of first decreasing and then increasing.The area of forest land,shrubs,and impermeable areas gradually increased.Except for the period from 2000 to 2010,the land use conversion was more intense in other periods,mainly manifested as the conversion of farmland to grassland and grassland to farmland.(2)Based on the analysis of the characteristics of regional rainfall and land use change,the impact of rainstorm characteristics and land use on the basin flood process is quantified by setting different scenarios.The results indicate that under uneven spatial distribution of rainfall,floods pose a greater threat to the safety of people’s lives and property in the watershed than under uniform spatial distribution of rainfall.The most unfavorable scenario is when the rainstorm center is in the lower reaches of the basin.Therefore,when the rainfall centers in the Hulu River Basin are mainly concentrated downstream,emergency response measures and disaster reduction and relief plans should be issued in advance.The order of peak flow and peak water depth under different land use scenarios is:2010 land use>2000 land use>1985 land use>2020 land use>generalized water and soil conservation measures>returning farmland to grassland>returning farmland to forest.Explaining that returning farmland to forest,returning farmland to grass,and other soil and water conservation measures mainly have a inhibitory effect on runoff.Under the combined action of rainstorm characteristics and land use,when the rainstorm center is in the downstream and the land use type is 2010 land use,the flood in the basin will pose the greatest threat to people’s lives and property;when the spatial distribution of rainfall is larger in the southeast and northwest regions,and smaller in the northeast and southwest regions,and the land use is for returning farmland to grassland,the reduction of peak flow and peak water depth can be maximized,which can protect the safety of people’s lives and property from loss to the greatest extent.Comprehensively compare the rainstorm characteristics and land use interaction scenarios with the rainstorm characteristics and land use change interaction scenarios,In addition to the scenarios of returning farmland to forest and grassland in the whole basin,the impact of rainstorm characteristics on flood in the basin is greater than that of land use change.(3)According to the future climate scenario data provided by GCMs and the future land use data predicted by CA Markov model,the characteristics of future rainstorm and land use change are analyzed.The results show that the number of future rainstorm days under four different forcing scenarios is 31 days,41 days,39 days and 44 days respectively,including five typical rain patterns,namely,the first type of single peak,the second type of single peak,the third type of single peak,the fourth type of double peak and the fifth type of uniform rain pattern;in the future,cultivated land,forest land,unused land,and impermeable areas will show a decreasing trend,while shrubs,grasslands,and water areas will show an increasing trend.Based on the future climate scenario data and land use prediction model,a prediction model of the Hulu River basin was established to predict the flood process of the Hulu River basin under different rainstorm and land use scenarios in the future 2023-2060.The results indicate that when the rainfall pattern in the watershed is single peak(with a rainfall peak behind it)or double peak,it poses a greater threat to the watershed,with a maximum peak flow of 3232.58 m3/s and a maximum peak water depth of 10.28 m.Except for the SSP2-4.5 scenario where there is no significant difference between different rain patterns,there are significant differences among different rain patterns in the other three scenarios.The order of peak flow and peak water depth under different land use scenarios in the future is:2060 land use>2050 land use>2040 land use>2030 land use.The land use data of the next four periods will have a certain reduction effect on peak flow and peak water depth,and the impact of future land use changes on flood processes will gradually decrease,The variation ranges of peak flow and peak water depth are 2.85%～21.46%and 0.18%～17.97%,respectively.