| Over the past 20 years,global warming has had a significant impact on the warming and humidification of the Tibetan Plateau,and profound changes have occurred in the ecological environment,glacier cover,lake complexes and river systems in the Hoh Xil region.As the snow line receded and glacier snowmelt increased due to climate change,the hydrological situation of the lakes in the Hoh Xil region,represented by Zhuonai Lake,Kusai Lake,Heidinor Lake and Salt Lake,has changed significantly in terms of water balance,water storage capacity and water body area.In particular,from mid to late August to early September 2011,due to the continuous strong rainfall,the water surface of Zhuonai Lake in the hinterland of the Hoh Xil region rose rapidly,and a large amount of water overflowed from the lake in the southeast,and the overflowed water flowed into Kusai Lake through the washed out flood ditch and the Kusai River,causing a significant increase in the surface area of Kusai Lake due to the rapid increase in water volume,and leading to a similar situation in Heidinor Lake downstream.The water from the Heidinor Lake outflow eventually enters the Salt Lake.The top-down hydraulic connection between Zhuonai Lake,Kusai Lake,Heidinor Lake and Salt Lake was established by the Zhuonai Lake outburst,and Salt Lake,which is located at the downstream end of the basin,became the final"recipient"of surface runoff and continues to expand.In view of the rapid changes in the lake population in the Salt Lake basin and the potential for flooding to some extent,systematic long-term monitoring of the lakes in the Hoh Xil region is essential.In order to understand the changes of plateau lakes under the influence of climate warming and humidification on the Tibetan Plateau,and to solve the problems of monitoring difficulties and lack of basic data for plateau lakes,this paper takes the core area of Hoh Xil from Zhuonai Lake to Salt Lake Basin as the study area(Zhuonai Lake,Kusai Lake,Heidinor Lake,and Salt Lake),and intends to obtain multi-source data from Zhuonai Lake to Salt Lake to investigate the causes of changes in the basin by obtaining the natural environment and the scarcity of basic data.The area and water level of the four major lakes in the basin were monitored dynamically for a long time,and the measured underwater topographic data were used to analyze the changes in water volume,and the causes of the changes in the lakes were discussed in combination with the m eteorological data analysis.The main findings and conclusions are as follows.(1)Normalized Difference Water Index(NDWI),Modified Normalized Difference Water Index(MNDWI),Enhanced Water Index(EWI)and New Water Index(NWI)were used for water body extraction in the study area,respectively.NDWI can perform the extraction task better,and the method is simple and applicable.NDWI was used for area extraction of the four lakes,and it was found that the time nodes of lake changes were basically the same,from 1989 to 2001,the area of the lakes all showed different degrees of decline;from 2001 to 2010,the area of the lakes began to rise,and the magnitude was greater than the decline before 2001;from 2011 onward,the Zhuonai Lake located in the upper reaches overflowed at the southeastern lake mouth,and the downstream After 2012,the area of the lake began to stabilize because of the influence of the overflow of the Zhuonai Lake,Kusai Lake and Heidinor Lake,and the Salt Lake began to expand steadily because it became the recipient of water from the whole basin.(2)Using Jason and Cryosat-2 satellite altimetry data,the water level changes of Kusai Lake and Zhuonai Lake and Salt Lake were monitored respectively,and the water level time change series of the lakes were constructed,and the correlation analysis between the water level data of each lake and the lake area extracted by Landsat was performed,and the correlation coefficients were all greater than 0.96(P<0.01),and the water level and area of the lakes had good consistency in time change.Using the observed water level and area values of the same period in Zhuonai Lake,Kusai Lake and Salt Lake,the water volume changes of the lakes before and after the overflow of Zhuonai Lake in 2011 were calculated based on the empirical formulae,and the water volume of Zhuonai Lake decreased by 2.69 billion m~3,while Kusai Lake and Salt Lake increased by 2.02 billion m~3and 1.32 billion m~3.(3)The reservoir volume curves of the lakes were constructed based on the underwater topographic data and SRTM data of Kusai Lake and Salt Lake,and the water volume changes of the lakes were calculated.The results showed that the overall increase in water volume of the Salt Lake from 1989 to 2018,with the largest increase occurring in 2011-2012,followed by 2016-2018,with an increase of 1,204 and 1,175 million m~3,respectively;the decrease in water volume occurred from 1989 to 1995,with a decrease of 0.2 6 billion m~3.The process of change in Kusai Lake is similar to that of Salt Lake,and it is basically the same as the change in Salt Lake until 2000,when the volume of water in the lake decreased by 133 million m~3;from 2001 to 2010,the volume of water increased by 516million m~3,while Salt Lake increased by only 38 million m~3;in 2011,an overflow occurred in Zhuonai Lake,which increased the volume of water in Kusai Lake by 2.156 billion m~3;In 2012-2018,the water volume decreased by 0.32 billion m~3,while the water volume of the Salt Lake continued to increase after 2011.(4)Trend analysis of meteorological data from 1989-2018 with linear propensity estimation,sliding average method and Mann-Kendall trend analysis revealed that rainfall and temperature showed an increasing trend,while evaporation showed a decreasing trend.There is a good consistency between lake changes and rainfall and temperature changes.Rainfall changes showed that the lake began to expand significantly in 2005 when the precipitation turned from low to high and increased in magnitude;after 2010,the rainfall increased significantly and began to exceed the significance level 0.05 threshold.Temperature changes showed that the temperature in 2003 changed abruptly and gradually increased beyond the significance level of 0.05 threshold,indicating that climate warming and humidification accelerated the expansion of the regional lakes. |
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