Volumetric analysis of a playa lake using SWOT data: An improved understanding of the inflows to Kati Thanda-Lake Eyre

Kati Thanda–Lake Eyre (KT-LE) is the largest terminal lake in Australia and the fourth largest worldwide. It is fed by the Lake Eyre Basin (LEB), the country’s largest internal drainage system. The LEB covers nearly one-seventh of the landmass area of Australia. The lake serves as a focal point for receiving inflow from tributary channels, making it pivotal in understanding the water balance in the drylands of the country, particularly amidst climate change. Unfortunately, due to its remoteness and vast size, no comprehensive water storage monitoring is available. However, the recent launch of the Surface Water and Ocean Topography (SWOT) satellite offers a promising solution for water monitoring in areas with limited in situ data at a 21-day frequency, with very high accuracy. In this study, we applied a method to estimate direct water storage from SWOT data, integrated with Sentinel-3 data, achieving an high level of precision. The method was applied to the 2024 filling event of Kati-Thanda to quantify event-scale water storage changes (surface area: 910 km2; maximum depth: 1.42 m and volume: 0.82 km3). The derived water depth and surface water extent exhibited satisfactory performance, showing strong agreement with both optical satellite masks (Landsat 8 and Sentinel-2) and ICESat-2 height measurements. The overall mean absolute percentage error (MAPE) for surface water extent was 15.1% for Landsat 8 and 14.4% for Sentinel-2. The estimated water depth demonstrated high precision, with a root mean square error (RMSE) of 0.30 m and a MAPE below 20% when compared with ICESat-2 data. Inherent limitations, such as bathymetry quality, sample size, and inundation coverage, were identified. Overall, the proposed method demonstrates its feasibility for monitoring direct water storage in KT-LE. This method has the potential for use in monitoring lake storage in other ungauged playa lakes and assessing long-term variability with similar climatic and terrain challenges.