Analysis Of Runoff Changes In The Upstream Of Sanggan River Basin Under Climate Change And Human Activities

In recent years,the frequent occurrence of extreme weather has caused huge losses to human society and nature.At the same time,with the needs of economic development,human activities have been intensified.Under the joint action of climate and human activities,the spatio-temporal distribution of available water in a basin has changed,and the hydrological cycle process has been changed to varying degrees,seriously affecting the production and confluence process of a basin.A series of water problems such as water shortage have become important factors restricting economic development and production and life.Therefore,it is necessary to understand the causes of runoff changes in different basins and separate the impacts of climate change and human activities on runoff,so as to provide important guarantees for water resources management and sustainable development.In this thesis,the upper Sanggan River basin is selected as the research object.Based on the analysis of the change characteristics of hydrometeorological elements,the SWAT model of the basin in the base period is constructed,and two methods based on the principle of regression analysis are combined: The relative contribution rates of meteorological factors and human activity factors causing runoff changes were calculated by the method of slope change rate of cumulative quantity and the method of elastic coefficient.The influence of precipitation and temperature on runoff during the changing period was further separated by using hydrological simulation combined with scenario simulation.The main results are as follows:1.The evolution law of hydrometeorological elements shows that precipitation presents an insignificant increasing trend,while air temperature,potential evapotranspiration and runoff present a significant decreasing trend.The periodicity of the whole series of precipitation and runoff depth is obvious in the first main cycle time scale,and the periodicity of potential evapotranspiration and temperature is obvious in the second and first main cycle time scales after 1995.The abrupt change of precipitation occurred in2011,and the abrupt change of air temperature occurred in 1994.The abrupt change time of potential evapotranspiration near the end time is not meaningful,and the abrupt change time of runoff depth is 1985.2.Based on the change characteristics of hydrometeorological elements,the time series of the study area is divided into three stages,namely,the base period(1970-1984),the change period I(1985-1993),and the change period II(1994-2021).The SWAT model was constructed in the base period,in which the correlation coefficient and Nash coefficient of the model rate and verification period were above 0.70,indicating that the model has certain applicability in the study area and can be used in the simulation of runoff change in the study area.3.Three methods were used to analyze the attribution of runoff changes,and the results showed that compared with the baseline period(1970-1984),human activities were the main cause of runoff reduction during the change period,and the influence of climate factors was relatively small.The contribution rates of climate factors to runoff reduction in phase I and Phase II ranged from 6.90%-11.87% and 24.6%-31.74%,respectively.The contribution rates of human activities to runoff reduction ranged from 88.13%-93.10% and68.26%-75.40%,respectively.Furthermore,SWAT model and scenario simulation method were used to separate the contribution rates of precipitation and temperature to runoff reduction among climate factors,and it was concluded that temperature variation was the main climate factor for runoff reduction.4.Seven periods of land cover type data from 1980 to 2015 were selected to analyze the land use situation and transfer process,collect raw coal production data and field survey in the study area to understand the basin situation,and analyze the main human activities in the study area.The main human activities for the decrease of runoff in the change phase I were the conversion of cultivated land,the main human activities for the decrease of runoff in the change phase II were the conversion of forest land and construction land,the continuous increase of raw coal production in the change phase II,and the destruction of geological structure during and after mining were also the reasons for the decrease of runoff.