Impact Of Environmental Change On Water Resources In Mountainous Area Of Manas River Basin

Object:In arid areas of northwest China,precipitation is scarce,evaporation is intense,and water resources are extremely scarce.Manas River Basin is a representative basin in northwest China,which belongs to a typical"mountain basin system",and its main water sources are mountain precipitation and glacial melt water.Environmental changes lead to changes in hydrological cycle,which greatly affect the spatial and temporal allocation of water resources in the basin and exacerbate the contradiction between water supply and demand in the basin.Human social and economic activities crowd out ecological water use in the watershed,which seriously endangers the sustainable development of the watershed ecosystem.Studying the spatiotemporal changes of blue and green water resources in the basin from the perspective of ecological hydrology is of great significance to the rational planning of water resources in the basin.Methods:Based on the hydrometeorological data and land use data of the mountain area in the Manas River Basin,we analyzed the evolution characteristics of hydrometeorological elements and the underlying surface in the mountain area.We constructed the primary database of the SWAT model in the mountain area.The SWAT model was used to simulate the blue water and green water resources in mountainous areas to explore their spatiotemporal evolution.By combining the influencing factors of environmental change under different historical scenarios,the contribution and contribution rate of environmental change to the change of blue water and green water resources in mountainous areas were quantitatively evaluated.The main research results are as follows:Results:(1)The average annual runoff in the mountainous area of the Manas River Basin was 12.95×10~8m~3.The annual runoff showed a significant increasing trend,with a sudden change in 1995 and a 23-year oscillation main cycle.The average annual precipitation in the mountainous area was 310-680mm,which was higher in the south than in the north.The precipitation in the mountainous area had an abrupt change around 1988,showing an obvious increasing trend.The annual mean temperature in the mountainous area ranged from-10-5℃,showing a significant increasing trend with significant intra-annual difference,and decreasing from north to south spatially.The structure of land use types was stable in mountainous areas,while forest land,grassland and cultivated land were interconverted in low mountainous areas.(2)SWAT model could well reconstruct the hydrological process of the mountain area in the Manas River Basin.During the calibration period(1982-1995):NSE=0.84,R~2=0.91,R_e=14.20%.Validation period(1996-2015):NSE=0.74,R~2=0.81,R_e=4.50%.The three performance indicators all reached good evaluation levels in the rate period and validation period,and the SWAT model constructed in this study can support the follow-up research.(3)The average annual amount of blue water,green water flow,and green water storage in the mountainous area was 259.90mm,208.71mm,and 28.46mm,respectively,with a small gap between the amount of blue water and green water.The temporal trends of blue water,green water flow,and green water storage were not synchronous,and showed an increasing trend as a whole.The abrupt changes of blue water and green water flow occurred in 1988,which was consistent with the abrupt point of precipitation in the mountainous area.In terms of spatial distribution,the amount of blue water resources was high in the east and west and low in the middle,while the green water flow was high in the middle and low on both sides,and the green water storage decreased from southwest to northeast.(4)Under the comprehensive influence of environmental changes,the changes of multi-year average values of blue water,green water flow,and green water storage from the base period were 101.15mm,-17.45mm,and 3.30mm,respectively,and their change rates were 45.38%,-9.24%,and 12.56%,respectively.Climate change was the dominant factor for the increases of blue water,green water flow,and green water storage in mountainous areas.The contribution of climate change to the changes of blue water,green water flow,and green water storage was 51.59mm,33.03mm,and 3.30mm,with contribution rates of 51.00%,-189.33%,and 100.00%,respectively.The contribution rates of land use to the changes of blue water,green water flow,and green water storage were 34.93%,206.50%,and-273.82%,respectively.Conclusion:The proportion of blue water and green water resources in the Manas River basin was close,and the green water development potential was high.Climate change was the main influencing factor for the increase of blue water and green water resources in the mountainous area.