Comparative Study On Lake Area Changes And Influencing Factors In Nam Co And Selin Co During 1976-2021

As a part of the terrestrial hydrosphere,lakes participate in the water cycle of nature.The change of lake area affects the balance of the ecosystem in the Qinghai-Tibetan Plateau.Nam Co and Selin Co are two of the largest typical lakes in Tibet.Exploring the response of the two lakes to climate change can provide theory for studying the evolution mechanism of lakes in the alpine region and formulating ecological and environmental protection measures.In this study,Nam Co and Selin Co lakes on the Northern Tibetan Plateau were taken as examples.Based on Landsat series remote sensing images lakes and glaciers in Nam Co and Selin Co watershed from 1976 to 2021,the annual lake area and glacier area were obtained through interpretation,and combined with the data of temperature,precipitation and evaporation of meteorological elements.The change characteristics of lake water area and glacier area were analyzed by mathematical statistics method,and the change rules of temperature,precipitation,evaporation and glacier area were further explored,and the response of temperature,precipitation,evaporation and glacier to the change of lake area was discussed.The conclusion is as follows:(1)The lake area of Nam Co and Selin Co showed a significant growth trend from1976 to 2021.The area of Nam Co Lake increased from 1950.95 km~2 in 1976 to 1986.00km~2 in 2021,an increase of 2.90%,with less fluctuation(CV=1.64%).The lake area changed abruptly in 2001 and experienced a change process of dry period,flat period and abundant period.The lake area of Selin Co increased from 1660.74 km~2 in 1976 to 2263.58km~2 in 2020,with an increase of 36.30%.The lake area fluctuated greatly(CV=12.65%).In2002,the lake area had a sudden change and experienced a trend from dry period to abundant period.The average growth rate of lake area in Selin Co was higher than that in Nam Co.(2)The annual average temperature and precipitation in Nam Co and Selin Co watershed showed a significant increasing trend,while evaporation showed a decreasing trend.The average annual temperature in Nam Co and Selin Co showed a significant increasing trend(P<0.01).The average annual temperature was 7.04℃and 8.05℃,with an increase rate of 16.98%and 16.69%,and the growth rates were 0.33℃/10a and 0.36℃/10a,respectively.Abrupt changes occurred in 2003 and 2005,respectively.Precipitation in Nam Co basin and Selin Co basin showed a significant increasing trend(P<0.05),the average annual precipitation was 378.27mm and 383.16mm,respectively with coefficient of variation was 9.22%and 21.24%,and the abrupt changes occurred in 1998 and 1997,respectively.The annual average evaporation in Nam Co basin and Selin Co basin was1596.27mm and 1677.72mm,respectively,and the decreasing rates were 270.22mm/10a and251.96mm/10a,respectively.The abrupt changes occurred in 2012.(3)The area of the main glacier in the western section of Nianqing Tanggula and the main glacier in Selin Co basin,Geladandong,showed a significant decreasing trend.The decrease rate of glacier area in the west section of Nianqing Tanggula was 230.97 km~2/10a,the average annual area was 1340.75 km~2,the coefficient of variation was 41.72%,and the abrupt change occurred in 2014.The decrease rate of Geladandong glacier area is 77.74km~2/10a,the mean area of the perennial area is 932.40 km~2,and the coefficient of variation is 9.32%,without mutation.(4)The variation of Namco was mainly affected by temperature,precipitation and evaporation,while that of Selin Co was mainly affected by atmospheric temperature and glacial area.There was a significant positive correlation with temperature and precipitation(P<0.05),a significant negative correlation with evaporation(P<0.01),and an insignificant negative correlation with glacier area(P>0.05).There was a significant positive correlation with air temperature(P<0.05),and a significant negative correlation with glacier area(P<0.01),but no significant correlation with precipitation and evaporation(P>0.05).The accelerated melting of ice and snow caused by increasing temperature and thus increasing surface runoff is the main reason why Selin Co area exceeds Namco area.