Impacts Of Changing Environment On Blue And Green Water Resources Of The Min-Tuo River Basin

With the rapid development of social economy and population growth,the process of urbanization is accelerating,which leads to the deterioration of water shortage environment and the crisis of water resources.Human activities and climate change are important factors that affect the stability and healthy development of ecosystem,and both of them will lead to the change of watershed runoff mechanism.Among them,human activities are closely related to the change of land use,and climate change is mainly related to the changes of meteorological indicators such as precipitation and temperature.In the traditional water resources evaluation,the available water resources only focus on the blue water resources,while the research on the green water resources,which is of great significance to the watershed ecosystem,is still shallow,and the green water is the direct water source for economic crops such as food production,which is crucial to the growth of crops.At present,most of the researches on blue-green water are focused on small and medium-sized basins,but few on large-scale basins.Min-Tuo River are the"four living"important water sources in Chengdu Plain.This paper takes Min-Tuo River Basin as the research object,with the help of soil and water assessment tool Tool,SWAT),from the perspective of hydrological cycle,analyzed the hydrological and meteorological data of Min-Tuo River Basin from 1979 to 2014,explored the temporal and spatial distribution characteristics of blue-green water in the basin,simulated different land use/cover scenarios and the law of blue-green water change under future climate change.The results are as follows:(1)In this paper,the Swat database of Min-Tuo river basin is constructed.The basin is divided into 89 sub basins and 1929 hydrological response units,Hrus),the runoff is calibrated and verified by SWAT calibration and uncertainty programs(swat-cup).During the calibration and verification period,the correlation coefficient R~2 of 7 hydrological stations is greater than 0.6,and the Nash coefficient NSE is greater than 0.5,which indicates that SWAT model has good applicability in the research area.(2)A two-year warm-up period is set for the operation of the model,and the simulation result is the blue and green water resources from 1981 to 2014.The results show that the average annual precipitation in the study area is about the sum of the average annual blue-green water resources,and the simulation effect is good.From 1981 to 2014,the green water resources increased,with an average growth rate of 0.24mm/year.The blue water resources showed a trend of fluctuation reduction,with an average reduction rate of2.48mm/year.The water resources of the whole basin showed an average reduction rate of1.65mm/year.The precipitation Kendall inclination z=-0.1087,and the blue water resources Kendall inclination z=-0.1729,indicating that the two decreased year by year,but the change was not significant Kendall inclination z=0.0232,indicating that green water resources are increasing year by year.Spatially,the amount of blue-green water resources gradually increases from north to South and then decreases,that is,the most in the middle reaches,the second in the lower reaches,and the least in the upper reaches.(3)Based on the data of land use in 1980,2010 and 1981-1994,1995-2014,the impacts of climate change and land use on the amount of blue-green water resources are explored based on scenario setting and variable control.The results showed that in 1980and 2015,the proportion of land use type area,cultivated land area in cultivated land,forest land and grassland decreased by 3.79%,grassland increased by 1.31%,and forest land decreased by 0.28%,From 1981 to 1994,the contribution rate of land use to the annual blue-green water resources was 99.08%,50.46%;from 1995 to 2014,the contribution rate of land use to the annual blue-green water resources was 70.9%,56.9%;it indicated that the impact of land use change on the annual blue-green water resources was greater than that of climate change.(4)In the three years of high,flat and dry,the area with the largest proportion of green water is near the subbasins 26,28,31,38 and 39,which indicates that the water resources of these five subbasins and their adjacent areas are mainly green water resources.The middle and lower reaches are rich in water resources and have more green water,but the green water coefficient is small,indicating that the majority of the middle and lower reaches are blue water resources.(5)The amount of blue-green water resources is significantly different in different land use types,among which,the amount of blue water resources is cultivated land>forest land>grassland,while the amount of green water resources is cultivated land>forest land>grassland,and the cultivated land area accounts for 25%of the total area of the basin,but the contribution rate to the total amount of blue-green water is the highest,indicating that the cultivated land is extremely important for regional water resource allocation and change,and will occupy the next land management measures Importance.(6)In the future,the change of water quantity and blue-green water in the climate change condition will show the trend of decreasing fluctuation.The minimum precipitation is in 2070 and the maximum is in 2050.Compared with the average precipitation,it decreases by 41.6mm and increases by 41.4mm.The change of green water resource is not significant,but the annual average green water resource decreases by 12.1mm compared with 1980-2014.The maximum amount of blue water is 576mm in 2050,the minimum amount is 489mm in 2070,which is a relative decrease of 87mm.The overall average rate of decrease in 2020-2100 is 6.44mm/a.The decrease in precipitation in the next 81 years will mainly lead to the decrease of blue water resources.