EOMF-29. Leveraging ICESat-2 and Landsat satellites for global-scale reconstruction of lake water levels over decadal scales

Lakes store 87% of Earth’s surface freshwater, providing important water supplies and many essential ecosystem services. Climate change and anthropogenic activities are increasingly threatening lakes, as evidenced by record-low levels in some of Earth’s largest water bodies. Yet, continuous monitoring of lake levels is rare at a global scale due to the sparse in-situ gauging network and the limited monitoring capacity of existing satellite radar altimeters on inland water levels. To date, the majority of Earth’s large lakes (> 100 km2) do not have continuous water levels spanning at least one decade. Here, we propose a novel proxy approach to derive water levels over recent decades (1992 to the present) based on satellite observations of water areas and lake bathymetry using 30-m Landsat images and a recently launched laser altimeter ICESat-2 with high-resolution elevation measurements. We leverage a recently developed algorithm to construct high-frequency water area time series using both cloud-free and partially cloudy images. We derive lake bathymetry by mapping the extents and elevations of isobaths using ICESat-2 and a 30-m water occurrence map. The derived lake bathymetry was used to convert water areas to water levels. We evaluate this method on 428 lakes worldwide with documented long-term water levels that were directly observed from satellite radar altimeters. Given better spatial coverages of Landsat and ICESat-2 missions compared with radar altimeters, the proposed method here can be potentially used to conduct an improved global inventory of time-varying lake levels and thus inform water resources management to a greater extent.