Geographical Calculation Of Runoff Change And Drought And Flood Disasters Dynamics In The Yellow River Basin Under Future Climate Change

In 2019,the Chinese government formulated the ecological protection and highquality development of the Yellow River Basin as a major national development strategy.At the same time,it also clearly pointed out that there are still some problems to be improved and solved in the Yellow River Basin.Global change aggravates the uneven distribution of water resources in the Yellow River Basin,resulting in the increase of the probability of drought and flood disasters in the Yellow River Basin,which has a serious impact on the production and life of human society,and also restricted the high-quality development of the regional economy.Therefore,it is urgent to analyze the influencing factors of runoff change in the Yellow River Basin under the background of global environmental change,and evaluate the change trend of runoff and meteorological drought in the Yellow River Basin in the future,which can provide certain scientific basis for formulating policies for improving the regional environmental conditions and ensuring the high-quality development of the region.The research contents of this paper can be divided into four parts:(1)Based on the meteorological observation and runoff observation data of the Yellow River Basin,the Budyko hypothesis is used to quantitatively analyze the contribution of climate factors(precipitation and evaporation)and human activities to runoff changes at Toudaoguai,Huayuankou and Lijin stations of the Yellow River;(2)A soil and water assessment tool(SWAT)model suitable for the Yellow River Basin was established to quantitatively analyze the sensitivity of land use and climate change to runoff change in the Yellow River Basin.The functional relationship between climate factors(precipitation,daily maximum temperature and daily minimum temperature)change and runoff change in the Yellow River Basin is obtained,and the influence mechanism of climate factors(precipitation,daily maximum temperature and daily minimum temperature)on the runoff change of the Yellow River Basin is clearly demonstrated;(3)Firstly,the land use data of the Yellow River Basin in 2050 under two development scenarios of status quo continuation and ecological protection are simulated by CAMarkov model.Then,the changes of mean and extreme runoff in the Yellow River Basin in the middle of the 21 st century(2040-2060)under the two land use change scenarios(status quo continuation and ecological protection)and climate change were simulated respectively;(4)The aridity index(IA)and standardized precipitation evaporation index(SPEI)of the Yellow River Basin in the future(2021-2099)are calculated for evaluating the trend of meteorological drought in the future.The following conclusions are obtained:(1)Based on Budyko hypothesis,the contribution rates of climate factors(precipitation,evaporation)and human activities to runoff change of Toudaoguai,Huayuankou and Lijin hydrological stations are calculated,which are 14.90%,1.02% and 84.07%,26.69%,0.04% and 73.27%,17.18%,-0.45% and 83.27% respectively.On the whole,human activities are the most important influencing factor of runoff reduction in the Yellow River Basin,and the impact of precipitation change on runoff reduction is more significant than that of reference evaporation change.(2)The order of influence degree of cultivated land,forestry land and grassland on runoff increase in the Yellow River Basin is cultivated land > grassland > forestry land.(3)The relationship between the precipitation change ratio and the change rate of the average runoff and Q95 extreme runoff of the four hydrological stations in the past 21 years is an upward parabola function.In addition,it can be found that the influence of precipitation change ratio on annual average runoff change rate is greater than that on Q95 extreme runoff change rate.The relationship between the precipitation change proportion and the runoff proportion of spring and winter of the four hydrological stations are all a downward parabola function,and that of the four stations in summer and autumn are all an upward parabola function.(4)The increasing value of daily maximum temperature and daily minimum temperature have an upward parabola response function relationship with the change rate of average runoff and Q95 extreme runoff at Lijin and Sanmenxia hydrological stations,and downward parabolic response function relationship with the change rate of average runoff and Q95 extreme runoff at Toudaoguai and Tangnaihai hydrological stations.The increase of daily maximum temperature and daily minimum temperature will lead to an increase in the proportion of runoff in summer and autumn,and both will lead to a significant decrease in the proportion of runoff in spring and winter,which indicates that the increase of temperature will aggravate the concentration of runoff distribution within a year,make water resources distribution more unbalanced,and increase the risk of drought in spring and winter.(5)Compared with the base period(1970-1990),the average runoff of most hydrological station in the Yellow River Basin in the middle of the 21 st century(2040-2060)shows an increasing trend,and the probability of flood disaster increases.(6)Compared with the base period(1970-1990),the proportions of spring runoff of the four hydrological stations in the middle of the 21 st century(2040-2060)in the Yellow River Basin show a decreasing trend.The proportions of winter runoff tend to increase,while the proportions of summer and autumn runoff increase or decrease differently.(7)Compared with the base period(1970-1990),the proportion of monthly runoff in April,May,June,July and October tend to decrease,and the proportion of monthly runoff in January,February,August,September and December tend to increase.(8)Compared with the RCP-LUC1(status quo continuation)scenario,the increase of average runoff under the RCP-LUC 2(ecological protection)scenario is greater,but the probability of flood disaster decreases.(9)The meteorological drought of the Yellow River Basin in the future will be intensified.With the increase of radiation forcing level,the regional scope of the Yellow River Basin is increasing,and the speed of drought aggravation is also increasing.In addition,Lanzhou?Toudaoguai and the middle reaches of the Yellow River are the regions with high frequency of drought in the future.Summer is the season with the highest frequency of drought in the upper reaches,middle reaches and lower reaches of the Yellow River.