Surface-Water-Level Changes During 2003-2019 in Australia Revealed by ICESat/ICESat-2 Altimetry and Landsat Imagery

Surface-water-level changes reflect Earth's water resource variations (e.g., trends and fluctuations) and they are helpful to understand potential drivers (e.g., climate change and human activities). Currently, Australia is facing serious water crisis owing to rainfall shortage and climate change, and national-scale data set on surface-water-level changes is required for supporting sustainable water resource management. Here, we used all Landsat Thematic Mapper (TM)/Enhanced Thematic Mapper (ETM)+/Operational Land Imager (OLI) data available on Google Earth Engine to obtain annual surface water during 2003-2019 and produced 1506 boundaries of water bodies with areas greater than 1 km2 across Australia. The produced surface water map in Australia is more accurate than the existing global lake databases (e.g., the Global Lakes and Wetlands Database), which can be downloaded for free. Then, 52 water bodies (lakes and reservoirs) with areas larger than 1 km(2) and available Ice, Cloud, and land Elevation Satellite (ICESat/ICESat-2) data for more than 5 years were combined to estimate trends in surface water levels in Australia. Across Australia, from 2003 to 2019, the area-weighted mean of water level change rates is -0.046 m/year with 17 lakes (32.7%) with increasing water levels and 35 lakes (67.3%) decreasing with water levels. In detail, the largest lakes (>100 km(2)) dominate the total change trend and most of the largest lakes underwent decreasing trend (-0.046 m/year), whereas the mean water levels of small lakes (<10 km(2)) increased in the past 17 years. In situ water levels of three typical lakes/reservoirs were used to validate our estimation results, which exhibited a very good agreement (R-2 = 0.98).