| Global warming and the frequent occurrence of extreme weather events have constantly an impact on the underlying surface conditions of basin and have profoundly affected the hydrological process of basin.Qinghai Lake Basin in the northeast of Qinghai-Tibet Plateau has always been a hot area for the study of environmental evolution in inland river basin because of sensitivity to climate change.In the past,a series of ecological and environmental problems such as grassland degradation,intensified desertification,and lake water level decreased continuously had become prominent in Qinghai Lake Basin,but in the last decade,lake water level has continued to rise,the state of grassland has improved,and the area of desertification has stabilized.For the above phenomenon,to find out the evolution law of hydrological elements,and to explore the relationship between climate factors and underlying surface changes and hydrological processes,that has reference value to the water resource management and rational allocation in the basin,to provide forward-looking significance for the protection of rare and endangered animals and plants,and to make an important contribution to the sustainable development of regional economy and society.There is no serious interference from human activities such as large-scale water conservancy projects in Qinghai Lake Basin.The change of underlying surface mainly refers to the change of surface cover.Based on the Budyko theory and the long-term meteorological,hydrological and remote sensing data,this paper comprehensively analyzed the evolution law of climate change,extreme climate events and hydrological process elements from the perspectives of trend,mutation and periodicity,found out and quantified the response of hydrological process elements such as lake water level,runoff,evapotranspiration,and water storage variation to climate change and underlying surface change.Finally,different scenarios were set up to predict the evolution of hydrological processes in the basin.The main conclusions are as follows:(1)This paper comprehensively analyzed the change characteristics of meteorological,hydrological and underlying surface factors in Qinghai Lake Basin.Qinghai Lake Basin has overall developed in the direction of warming and wetting.Among the climatic elements,the average temperature and precipitation separately showed a significant upward trend at the rate of 0.36?/10 a and 14.74m/10 a,the average wind speed and sunshine hours declined significantly at the rate of 0.09m/s/10 a and 146.49h/10 a,the potential evapotranspiration has slow upward trend.Among the underlying surface elements,the change of land use types was small,and65.59% of vegetation showed a trend of improvement,the area that had improved significantly accounted for 22.25%.Among the hydrological elements,the water level of Qinghai Lake fell obviously at the rate of 7.84cm/a from 1960 to 2004,and then rose fast at the rate of 13.80cm/a from 2005 to 2016,and the runoff increased slowly,and the evapotranspiration and water storage variation showed a significant trend of upward at the rate of 2.14mm/10 a and 7.51mm/10 a respectively.The spatial distribution of key hydrometeorological elements was heterogeneous in different periods.The increase rate of meteorological and hydrological elements in the western and northern of high latitudes and high elevations was faster than that in the eastern and southern regions.(2)The relationship between climate change,underlying surface change and hydrological process was illustrated.The elastic coefficients of precipitation,net radiation,air temperature,wind speed and relative humidity to runoff were 1.98,-0.64,-0.02,-0.16 and 0.55 respectively.Both runoff and precipitation had a main periodicity of 23 years,indicating that runoff was more sensitive to precipitation than other climate variables,and their change periodicity was highly consistent.The correlation coefficient between underlying surface characteristic parameters(?)and the lake water level difference(?h),runoff,watershed water storage was-0.38,-0.64,0.51 respectively,and passed the significance level test of 0.01.Since the 2000 s,the increase of precipitation was the leading factor for the increase of runoff,vegetation improvement was the result of increased precipitation and ecological environment construction,which was synchronized with increased runoff.(3)The contribution of climate change and underlying surface change to runoff and lake water level was quantitated.As temperature and precipitation were rising,the sensitivity of runoff to precipitation,potential evapotranspiration and underlying surface had increased.From 1960 to 2016,each additional 1mm of precipitation in the basin will increase runoff by 0.38 mm,and each additional 1mm of potential evapotranspiration will reduce runoff by 0.07 mm,and each additional 1 of underlying surface characteristic parameters will decrease runoff by 98.32 mm.Compared to reference period(1960-2004),the runoff increased by 25.42 mm and the contribution rate was 79.79% in the abrupt change period(2005-2016),and the underlying surface change which resulted in runoff increased by 6.44 mm,with a contribution rate of 20.21%.The influencing factors of underground runoff were analyzed quantitatively by using Principal Component Regression Analysis,the contribution rate of the climate to underground runoff was 88.43%,and the contribution rate of underlying surface to underground runoff was-11.57%.Finally,the contribution rate of climate change and underlying surface change to lake water level were93.02% and 6.98% respectively in Qinghai Lake.It showed that climate change was the leading factor of hydrological process change,and the underlying surface change also played a role in Qinghai Lake.(4)The evolution rule of extreme climate change and its relationship with hydrological process were clarifies.From 1960 to 2016,the warming indexes and extreme precipitation indexes showed a significant upward trend,and they were positively correlated with hydrological process factors such as the lake water level difference,runoff,evapotranspiration and water storage variation.Meanwhile the cold indexes showed a significant downward trend,and it was negatively correlated with hydrological process factors.Extreme hydrological events such as the total amount of extreme floods and extreme dry water showed a certain upward trend,and the correlation between extreme hydrological events and extreme precipitation events was higher than that of extreme temperature events.The main factor of extreme flood events is extreme precipitation events,especially extreme precipitation.Water storage variation was more closely related to precipitation,whereas evapotranspiration was more closely related to temperature.(5)In this paper,the evolution of hydrological process in the future was predicted in Qinghai Lake Basin.This paper confirmed that the potential evapotranspiration(PM)could use this empirical formula to modify the potential evapotranspiration calculated by Har formula in the study area.It was calculated that the time required to reach the state of water storage variation was 0 in the basin was at least 5a.We predicted the future development trend of climate,the underlying surface and hydrological process using the step of 5a.The Four kinds of climate change scenarios and the underlying surface change scenarios were set,the results indicated that runoff,evapotranspiration and water storage variation the future would increase,the lake water level would continue to rise. |
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