| The change of water resources in the water source area of the middle route of China's South-North Water Transfer Project plays a key role in water resources and ecological security of the water receiving area,water source area,as well as the middle and lower reaches of Hanjiang River.Since the 18th CPC National Congress,economic,political,cultural,social and ecological progress has put forward new requirements for water resources security and ecological security in this region.In addition,Hubei and Shaanxi provinces are planning new regional water diversion projects respectively,which makes the regional water resources allocation scheme more complex.However,climate change and the intensified human activities in recent years have reduced the inflow runoff of Danjiangkou Reservoir,posing a challenge to the increasing demand for water resources.Therefore,it is of great importance to study the spatiotemporal variation characteristics of precipitation and streamflow,as well as their driving mechanism in water source area.In this study,hydrometeorological data were collected from 34 meteorological stations and 21hydrological stations.Other data including reservoir,land use,soil and ndvi are also collected.Trend analysis,correlation analysis,regression analysis,spatial variation analysis,statistical significance test and double mass curves were used to analyze the spatiotemporal change characteristics of precipitation and streamflow in water source area,and then discussed their influencing mechanism.The main results are as follows:(1)The average daily precipitation(ADP)of annual,spring,autumn and winter showed a decreasing trend,and an increasing trend in summer,while the average daily precipitation on rainy days(ARP)showed an increasing trend.The multi-year ADP was 2.34 mm/d and the multi-year ARP was 7.2 mm/d.ADPs in spring,summer,autumn and winter were 2.09,4.27,2.64 and 0.34 mm/d,respectively,and ARPs in four seasons were 6.10,10.44,6.98 and1.88 mm/d,respectively.The multi-year ADP decreased slightly by-0.002 mm/d/a,and the range of ADP changes in spring,summer,autumn and winter were-0.006,0.005,0.010 and0.0003 mm/d/a,respectively.The range of ARP changes were 0.018,0.007,0.039,0.008 and0.005 mm/d/a,respectively.This is due to the decrease of light rain days and light rainfall,and the increase of heavy rain days and heavy rainfall.(2)The annual,spring,summer and autumn streamflow of main stream showed a decreasing trend,and increased in winter except for Huangjiagang station.The annual and seasonal streamflow in the main stream decreased by 0.878×10~8,0.108×10~8,0.294×10~8,0.405×10~8 and 0.13×10~8m~3/a.The rate of streamflow change of Huangjiagang station was-2.03×10~8,-0.03×10~8,-0.53×10~8,-1.17×10~8 and-0.4×10~8 m~3/a.The autumn was the season with the largest streamflow reduction.Except winter,the annual and other three seasons streamflow of the tributary station showed a decreasing trend,with the change rates of-0.06×10~8,-0.015×10~8,-0.029×10~8 and-0.012×10~8 m~3/a,while the winter streamflow showed an increasing trend with the rate of 0.002×10~8 m~3/a.The Huanglongtan station had the most significant variation in tributaries,and the rate of annual and seasonal streamflow changes were-0.42×10~8,0.007×10~8,-0.06×10~8,-0.22×10~8 and-0.25×10~8 m~3/a,respectively.(3)The streamflow of main stream and tributary stations showed obvious inter-decadal differences.The average annual streamflow of main stream stations was the highest in the1980s,with an average of 236.4×10~8 m~3,and the lowest in the 1990s,with an average of135.1×10~8 m~3.The streamflow of region control station,Huangjiagang station in the 1980s and 1990s were 437.89×10~8 m~3 and 262.75×10~8 m~3,respectively.The average streamflow in the 1980s and 1990s was 32.9×10~8 m~3 and 23.8×10~8 m~3,respectively.The inter-decadal variation of streamflow in tributary stations was similar to that in main stream stations,and the average streamflow in 1980s and 1990s was 32.9×108 and 23×10~8 m~3,respectively.(4)The streamflow change of main stream station was affected by dam construction,while the streamflow of tributary basin was affected by human activities such as land use and vegetation change.The large-scale water conservancy projects,Shiquan and Ankang reservoirs in the main stream of the Hanjiang river increased the winter streamflow by21.8%and 30.5%,respectively,while in the main tributaries,Huanglongtan reservoir in the Hanjiang river and Daulingzi reservoir in the Jiahe river increased the winter streamflow by75%and 50%,respectively.The impact of reservoir on annual and other seasonal streamflow was limited.The contribution of human activities to annual,summer and autumn streamflow in the tributary basins was 64.14%?164.65%,58.69%?341.04%and 68.9%?148.01%,respectively,and the spring streamflow was mainly affected by climate change.In summary,the significant decreased rainydays and increased average daily precipitation on rainy days has changed the local surface runoff process,which result in significant reduction in surface runoff.Land use and vegetation changes will aggravate the reduction unfortunately.These results were helpful to understand the problems of water resources management in the Middle Route of the South-to-North Water Transfer Project. |
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