Runoff And Sediment Variations And Its Response To Climate And Land Use In Yihe River Basin

The Yihe River Basin is located in the low mountains and hills of central and southern Shandong,and is one of the important tributaries of the Yishusi Water System in the Huaihe River Basin.The Yihe River Basin has a shortage of water resources,a fragile ecological environment,serious soil and water loss and prominent water use contradictions.It is of great scientific significance to study the impact of climate and land use changes on water and sediment changes in the basin in terms of coordinating of regional water and sediment relations,constructing ecological environment,promoting the sustainable use of water resources,and ensuring the economic and social sustainable development.This study takes the Yihe River Basin as the study area,analyzes the laws of land use change,runoff and sediment change,and climate change in the basin,and SWAT hydrological models are constructed to analyze the responses of runoff and sediment to climate and land use,meanwhile,based on global climate model and CA-Markov model,the runoff and sediment of the Yihe River Basin from 2019 to 2099 are estimated,and the integrated river basin management strategies are proposed.The main research conclusions are as follows:?1?From 1961 to 2015,the precipitation in the Yihe River Basin was mainly concentrated in July and August.The temperature was highest in June to August and lowest in January.The annual precipitation showed a slight decrease trend and the annual temperature showed a clear upward trend.The trends of monthly runoff and monthly sediment in the Yihe River Basin from 1961 to 2015 are basically the same,mainly concentrated in summer.The interannual changes of runoff and sediment are obvious.The annual runoff and annual sediment both showed a significant downward trend,which generally met the law of large water and large sand,and less water and less sand.There are periodic changes of time scales of 6a,7¹4a,15a,and 24a are common during runoff evolution,and periodic changes of time scales of 6a,10¹2a,and 25a in the sediment.?2?From 1975 to 2015,the land use structure of the Yihe River Basin was dominated by cultivated land and forest land,followed by grassland,construction land,and water,with the smallest unused land.The change in the area of land is shown as the continuous decrease of cultivated land and grassland,the rapid expansion of construction land,and the overall increase in forest land,waters and unused land.The comprehensive land use dynamics showed a volatile growth trend,and the transfer speed in land use types also fluctuated and increased.The transfer direction of land use types is mainly manifested the increased area of construction land mainly from cultivated land.The cultivated land is mainly converted to construction land,forest land and grassland,and forest land is mainly transferred from cultivated land and grassland.?3?Runoff and precipitation have good correlation and consistency;the impact of runoff on sediment is greater than that of climate on sediment.Human activities such as water conservancy project construction,water resources development and utilization,and land use change have a significant impact on runoff and sediment.Quantitative assessment of the contribution of human activities and precipitation to change in runoff and sediment using the cumulative slope change rate comparison method.The contribution rates of human activities and precipitation to changes of runoff during 1966²015 were 64.8%and 35.2%,respectively.The contribution rates of human activities and precipitation to change of sediment during1966¹975 were 73.5%and 26.5%,and the contribution rates of human activities and precipitation to change of sediment during 1976²015 were 73.8%and 26.2%,respectively.Human activities are the main reason for changes in runoff and sediment,which are far greater than the effects of precipitation.?4?The results of the SWAT distributed hydrological model showed that the monthly simulation results of runoff and sediment from 1961 to 2015 in the Yihe River Basin are better than the annual simulations.This model has good applicability in Yihe River Basin;Using the method of fixing one factor to change another factor,quantitatively distinguish the contribution rates of climate and land use changes to runoff changes are 41.58%and 58.36%,respectively,and model errors account for 0.06%;the contribution rates to sediment changes are 43.25%and 54.23%,respectively,and model errors account for 2.52%.It shows that land use change is the main factor for the change of runoff and sediment.?5?The BCC-CSM1.1,BNU-ESM,MRI-CGCM3 climate models in 2019²099 RCP4.5and RCP8.5 scenarios under the monthly average runoff are basically greater than the base period,the annual runoff growth trend under the RCP8.5 scenario is more Obviously.The monthly average sediment is basically the same as the base period in the non-flood season,and the annual sediment growth rate is larger under the RCP8.5 scenario.Compared with the base period,except for the S₄ food security priority scenario,the runoff and sediment of other land use change scenarios showed a downward trend.Under the coupling scenario of climate and land use change,the change of runoff mainly depends on climate change,while the amount of sediment depends on the combined effects of climate and land use change.Aiming at the possible climate and land use change in the river basin in the future,relevant policy recommendations for comprehensive watershed management were put forward.Land use structure should be optimized,the impact of climate change on water resources planning should be emphasized,and the sustainable development of the ecological environment should be promoted.