Satellite observed recent rising water levels of global lakes and reservoirs

Monitoring global lake/reservoir water level changes is needed to understand the global water cycle and investigate its potential drivers. The existing global water level products only cover lakes/reservoirs with large sizes (>100 km(2)). Here, Ice, Cloud, and land Elevation Satellite (ICESat) and ICESat-2 altimetry data with small footprints are employed to examine global water level changes for 22 008 lakes/reservoirs greater than 1 km(2). We report that 77.56% of them exhibited rising water levels over 2003-2021. Across the globe, 78.84% of lakes exhibit a rising water level, while the proportion for reservoirs is only 56.01%. Global lake/reservoir is estimated to experience a median water level change rate of +0.02 +/- 0.02 m yr(-1) over 2003-2021, and lakes have a larger water level rise (+0.02 +/- 0.02 m yr(-1)) than reservoirs (+0.008 +/- 0.14 m yr(-1)). We detect large-scale rising water levels in the Tibetan Plateau, the Mississippi River basin, and high-latitude regions of the Northern Hemisphere. Our calculation also suggests a negative relationship between the percentage of water level rise in lakes/reservoirs and population density for global river basins (r = -0.41, p-value < 0.05) and 11 hotspots (r = -0.48, p-value < 0.05). Our result suggests that inland water level has tended to rise in recent years under natural processes while human activities (i.e. with higher population density) can balance the water level rise via reservoir regulation. We find the existing datasets underestimated global water level rise, which may be caused by the exclusion of numerous small lakes/reservoirs. Our estimated global water level change rates (that include numerous small lakes with areas of 1-10 km(2)) can improve the understanding of global hydrological cycle and water resource management under the double pressure of climate warming and human activities.

Automated summary

This study used ICESat and ICESat-2 altimetry data to investigate global water level changes for 22,008 lakes/reservoirs greater than 1 km2. The results showed that 77.56% of the lakes/reservoirs experienced rising water levels from 2003 to 2021. Globally, 78.84% of lakes exhibited a rising water level, while the proportion for reservoirs was only 56.01%. Large-scale rising water levels were detected in the Tibetan Plateau, the Mississippi River basin, and high-latitude regions of the Northern Hemisphere. The study also found a negative relationship between the percentage of water level rise and population density in global river basins and 11 hotspots. The findings suggest that natural processes contribute to the rising inland water levels, while human activities can balance the rise through reservoir regulation. The study highlights the underestimation of global water level rise by existing datasets and emphasizes the importance of including small lakes/reservoirs in studying global hydrological cycle and water resource management.