Estimating the fluctuation of Lake Hulun, China, during 1975-2015 from satellite altimetry data.

Lake level, area, and volume changes can describe the fluctuation of water bodies. In this study, ICESat/Hydroweb and Landsat data recorded with irregularly time intervals from 1975 to 2015 were used to examine changes in lake level and area which were combined to indirectly estimate water volume variations of Lake Hulun. The time series of lake level, area, and volume variations of Lake Hulun exhibited a fluctuating trend from 1975 to 1984 and the mean value were about 542.57 m, 2065.76 km, and - 0.045 km, respectively and an increasing trends showed during 1984-2000. Lake Hulun revealed the fastest decrease in lake level (- 0.42 m/a), volume (- 0.83 km/a) from 2000 to 2009, and the fastest shrinking in surface area (- 33.88 km/a) during 2000-2012. There was a seasonal variation of water level and lake volume variations during 2009-2012 and the mean value were 539.98 m and - 5.72 km, respectively. From 2012 to 2015, a faster increasing trends were shown in water level, area, and volume variations with a rate of 0.73 m/a (the amount of change was 2.92 m), 81.95 km/a (the amount of change was 327.8 km), and 0.42 km/a (the amount of change was1.67 km), respectively. The lake level and area showed strong correlations for Lake Hulun (R  = 0.93). The water volume changes were in very good agreement for lake level changes (R  > 0.99) and surface area variations (R  = 0.92). Combining with lake level and area changes, the sum of lake volume variation of Lake Hulun was obtained and it showed a positive water budgets of 0.24 km during past 40 years. River and groundwater discharge, the pan evaporation, the net pan evaporation, and the water diversion project were reasons for the lake level, area, and volume variations in Lake Hulun. This study demonstrates that remote sensing data can be used as a source of information for monitoring comprehensively the fluctuation of large water bodies.