Remote Sensing Monitoring And Influencing Factors Analysis Of Lake Water Volume Changes In Central Asia

Lakes are nodes of the interaction between the terrestrial hydrosphere and soil,organisms,and atmosphere.They are extremely sensitive to global climate change.Lakes'spatial distribution and spatiotemporal changes reflect the impact of water resources and ecosystems of regional and global climate change,surface processes,human activities,etc.In recent years,under the combined influence of climate change and human activities,a large number of lakes have experienced deterioration in pollution,reduction in lake area,water level and water volume,degradation of ecological functions,and even gradual disappearance.Central Asia is located in the Eurasian hinterland of the middle latitudes of the northern hemisphere.It is the main arid/semi-arid region in the world,with sparse precipitation and strong evapotranspiration all year round.Lakes are extremely important water resources in arid and rainless Central Asia,and support the ecosystems in the region.In recent decades,under the combined influence of climate change and human activities,there have been great changes in lakes in Central Asia,which has caused a series of ecological problems and even caused ecological disasters.Therefore,it is very important for the water resources management in Central Asia to study the changing laws of lakes in Central Asia,and to analyze the role of climate factors and human activities in the process of the spatial and temporal dynamics of lakes.This paper selects 18 lakes in Central Asia and monitors their spatial and temporal changes over the past 20 years,and constructs a long-term series of lake area,water level and water volume change data sets for each lake.The Mann-Kendall trend test and Pettett mutation test were used to test each time series data,and the changes of each lake over the past 20 years were analyzed based on the results of test.In addition,combined with the meteorological data within the scope of a single lake basin and data related to human activities,the influencing factors of the spatiotemporal changes of the lake are analyzed.The main research contents and conclusions are as follows:(1)Using the optical image data of the Landsat series of satellites as the data source,a long-term series of land surface water datasets in Central Asia from 1995 to 2018 was extracted on the Google Earth Engine cloud computing platform using machine learning algorithms,and based on this Long-term series of datasets of lake area changes in Central Asia was constructed.Through the test and regular analysis of the lake area time series data set,it is found that the area of 7 lakes shows a significant upward trend,and the area of the North Aral Sea rises the fastest,with an average annual increase of19.111km2.The area of the 5 lakes shows a significant downward trend.The area of the South Aral Sea declined the fastest,with an average annual decline of 1158.1km2.The area of the remaining lakes fluctuated during the monitoring period,and there was no obvious change trend.(2)Based on the lake and reservoir water level data set products obtained by radar height measurement data,the annual average water level time series data set of lakes in Central Asia from 1995 to 2018 was calculated.Through the test and regular analysis of the time series data set of each lake,it was found that the water level of 7 lakes showed a significant upward trend,and the change of the water level of 2 lakes showed a relatively violent fluctuation and a slow upward trend,of which the fastest rise in the water level was Kayrakkumskoye reservoir,with an average annual increase of 0.222m.The water levels of the 6 lakes showed a significant downward trend,and the fastest drop in the water level was the South Aral Sea,with an average annual decrease of0.376m.The water level of other lakes fluctuated greatly,and there was no significant trend.(3)On the basis of the time series data of each lake area and water level,combined with empirical formulas,based on the water volume of the first monitoring year of each lake,the time series data set of the water volume changes of each lake from 1995 to2018 was calculated.Through the test and regular analysis of the time series data of each lake,it was found that the water volume of 7 lakes showed a significant upward trend,and the water volume of 2 lakes showed a relatively violent fluctuation and a slow upward trend,of which the fastest rise in the water volume was Lake Balkhash,with an average annual increase of 1.079 km~3.The water volume of the 6 lakes showed a significant downward trend,and the fastest decline in water volume was the Caspian Sea,with an average annual decrease of 17.472km3.The water volume of other lakes fluctuated greatly,and there was no significant trend.(4)Taking the Lake Balkhash as an example,the spatial-temporal dynamic changes of the Lake Balkhash area,water level and water volume from 1995 to 2018,the data correlation between the three factors,and the impact on the process of spatial and temporal changes of the Balkhash Lake caused by meteorological factors and human activities were analysised.The three factors of the Lake Balkhash area,water level and water volume showed a significant upward trend from 1995 to 2018,and the correlation between the three factors was extremely strong and the data consistency was good.The spatial and temporal changes of the Lake Balkhash are always affected by meteorological factors and human activities at the same time.Different stages are controlled by different factors.The decline stage is mainly affected by the interception of the Kapuchagai Reservoir,and the rise stage is the impact of the increased melting water of glaciers mainly caused by regional climate changes.