Seasonal Variation Of Lake Hydrology In China Based On Multi-source Remote Sensing

As a part of the earth’s hydrosphere,lakes play an important role in maintaining ecological balance,providing freshwater resources,and alleviating flood disasters.China’s lakes are numerous and widely distributed,with obvious regional characteristics,and are very sensitive to climate change.In the past few decades,the hydrological elements of lakes have changed significantly due to the frequent occurrence of extreme natural disasters(such as floods or droughts)due to the increasing climate warming and human intervention.Monitoring the seasonal variation characteristics of lake hydrology in China and discussing the reasons will help strengthen the scientific understanding of the seasonal hydrology of lakes in China and provide scientific and technological support for flood risk assessment and prediction in different regions of China.This study selects lakes above 1 km~2 in China as the research object,and uses satellite altimetry to quantify the seasonal variation characteristics of lake water level and water storage in China from October 2018 to September 2021,and explore the main influencing factors.To further understand the changes of lake hydrological elements in the eastern monsoon region,this study estimated the seasonal variations of water level and water storage of 29 large lakes(with an area>100 km~2)in the middle and lower reaches of the Yangtze River and the Huaihe River basin(the Yangtze-Huai River Basin)from 1990 to 2020.Finally,aiming at Poyang Lake,a typical lake with severe seasonal fluctuations,which is also the largest freshwater lake in China,a method is proposed to reconstruct the water area of the entire lake based on the partial cloud-covered Sentinel-2 image combined with Sentinel-1 image,and to encrypt the time series of water area and storage and to more effectively understand the inter-annual and intra-annual changes of water budget of Poyang Lake.The main conclusions are as follows:(1)1379 lakes can use ICESat-2 altimetry data to monitor dry(January-May)/wet(May-December)seasonal water level fluctuations,accounting for about 95%of the total lake area.The average seasonal variation of water level in 1379 lakes is 0.41 m,1292lakes with seasonal variation of water level less than 1 m,and 14 lakes with seasonal variation of water level greater than 3 m(such as Poyang,Dongting and Bo Lakes,etc).During the study period,the seasonal variation of the total water storage of 1379monitored lakes is about 66.76 Gt,with great spatial heterogeneity.The middle and lower reaches of the Yangtze River basin and the inland river basin of the Tibetan Plateau are the two basins that contribute the most to the seasonal variation of lake water storage.(2)In general,the average amplitude of seasonal changes in the water level of the plain lakes in the Yangtze-Huai River Basin is about 2.80±0.71 m.There are 12 lakes whose seasonal water level variation exceeds the average seasonal variation,accounting for about 41%of the total lakes.Poyang Lake(9.53±2.02 m)and Dongting Lake(7.39±1.29 m)are still naturally connected to the mainstream of the Yangtze River.The interaction between rivers and lakes is complex,and they are the two lakes with the largest seasonal changes.The total water storage capacity of the plain lakes in the Yangtze-Huai River Basin is about 37.38±14.19 Gt.The seasonal water storage variation of the plain lake groups in the Yangtze-Huai River Basin contributed about 33.25%to the terrestrial water storage variation.(3)From 2017 to 2020,a total of 113 partial clear Sentinel-2 images for Poyang Lake can be used to extract the block area to reconstruct the complete lake water area.By combining images based on Sentinel-1 and Sentinel-2,Poyang Lake can be monitored up to 13 times in a month with a time interval of 2-3 days.The water area and water storage capacity of Poyang Lake have strong intra-annual and inter-annual changes.The rainy season of Poyang Lake is from April to September,and the dry season is from October to March of the following year.The lake area fluctuates between 676.24 km~2 and 2978.62km~2,and the fluctuation of water storage is from 1.87 Gt to 16.62 Gt.