The Study On Spatiotemporal Variation Of Water Resources In Qinghai-Tibet Plateau And Its Driven Forces

In recent years,the climate of the Qinghai-Tibet Plateau has shown a trend of warm and humid change,which has greatly affected the distribution of water resources in the Qinghai-Tibet Plateau.Precipitation and runoff are important links in the process of water cycle and an important part of water resources.Analyzing the temporal and spatial variation characteristics of surface water resources,groundwater resources and runoff in the Qinghai-Tibet Plateau is conducive to grasp the current situation of water resources in the plateau and plays an important role in ensuring the safety of water resources in the Qinghai-Tibet Plateau.In this study,the factors of water resources in the Qinghai-Tibet Plateau are studied by means of univariate linear regression,Mann Kendall trend test and Morlet wavelet analysis.The main research contents and results are as follows:(1)Based on the relevant data of water resources bulletin of Qinghai Province and Tibet Autonomous Region,the temporal and spatial changes of surface and groundwater resources in cities and basins of the Qinghai-Tibet Plateau are analyzed.The results show that the water resources of the Qinghai-Tibet Plateau are mainly distributed in Nyingchi city and Shannan city in the southeast of the Qinghai-Tibet Plateau,Yarlung Zangbo River Basin and southern Tibetan river basins.From 1997 to 2018,the surface water resources and groundwater resources in Qinghai province increased significantly,with the rising rates of 9.83 billion m~3/10a(p=0.014)and 5.8 billion m~3/10a(p=0.007)respectively.The mutation point was around 2005.The amount of surface water resources in Tibet Autonomous Region showed an insignificant downward trend,with a downward rate of 2.52 billion m~3/10a(p=0.79),and the mutation point was in 2001;Groundwater resources showed a significant downward trend,which was-19.54 billion m~3/10a(p=0.00045),and the mutation point was in 2002.(2)The distribution and spatiotemporal variation of precipitation over the Qinghai Tibet Plateau are studied by using eight precipitation data sets from domestic and foreign scholars.The results show that the precipitation in more than two-thirds of the Qinghai-Tibet Plateau shows an upward trend,among which the source area of the Yellow River,the inland river basin,the Tarim River Basin and the middle reaches of the Yarlung Zangbo River have a significant upward trend.The average growth rate of the overall precipitation in the Qinghai-Tibet Plateau in recent 40 years is 3.52mm/a.However,the precipitation of Nujiang River,Lancang River and the source area of the Yangtze River in the southeast of the Qinghai Tibet Plateau showed a significant downward trend.Among all precipitation data sets,the CFMD data set made by Yang Kun and the data set made by he Yongli have the highest accuracy,with relative errors of 13.64%and 17.94%respectively.(3)The interannual variation,annual distribution,abrupt change and periodicity of runoff in various basins of the Qinghai-Tibet Plateau are studied.The results show that the runoff in most areas of the Qinghai-Tibet Plateau shows an upward trend.Among them,the runoff of the Yangtze River,Yarlung Zangbo River,Qaidam and Qinghai lake basins showed a significant upward trend,the Nujiang River and Lancang River Basins showed an insignificant upward trend,and only the main stream of the Yellow River showed a significant downward trend,and the change rate of each main stream was-16.03～35.94million m~3/10a.Each basin shows obvious monsoon distribution characteristics.The flood season is mostly concentrated in summer and autumn,and the flood season of main rivers accounts for 63.8～85.3%.Most watersheds show periodic changes of 3-4 time scales.The main cycles of the Yellow River,Yangtze River,Lancang River,Nujiang River and Yarlung Zangbo River basins are 21,7,16,24 and 16a respectively.(4)The double cumulative curve method is used to analyze the runoff of each watershed with significant changes,and the effects of natural factors and human activities on water resources are studied.The results show that except for the source area of the Yellow River,the main influencing factor of the significant change of runoff on the Qinghai-Tibet Plateau is the climate factor,and the contribution rate is between 60%～82%.Although the impact of human activities on water resources has gradually increased in recent years,natural factors are still the main factors affecting the change of water resources in the Qinghai-Tibet Plateau.Considering the influence of natural factors and human activities,precipitation change is the main factor affecting the quantitative change of surface and groundwater resources in the Qinghai-Tibet plateau.Soil water content and snow depth are also important factors affecting the decline of groundwater resources in the southeast of the Qinghai-Tibet Plateau.