Icesat-derived water level variations of roseires reservoir (Sudan) in the Nile Basin

The information of water level variations in lakes and reservoirs is essential for many applications such as water resources management. The conventional in-situ measurements of water levels based on gauge station are often rarely available or difficult to be shared to the public especially for lakes in the developing countries and transboundary basins. Satellite altimetry provides an alternative solution to obtaining water level variations in lakes. In this study, the laser altimetry product GLAS/ICESat L2 Global Land Surface Altimetry (ICESat-GLA14) data was used to derive water levels in a narrow long-shaped reservoir in the Nile Basin, i.e. Roseires Reservoir in Sudan. A total of 19 water levels were derived from ICESat-GLA14 during the period 2003-2009. Compared with the in-situ measurements, all 19 ICESat-derived water levels had a R² of 0.88 and RMSE of 138.80 cm. After excluding two water levels (occurred on June 21, 2004 and June 8, 2005) with very large standard deviation (> 1 m), other 17 ICESat-derived water levels were in excellent agreement with in-situ measurements with R² of 0.99 and RMSE of 16.96 cm. In practical situation, the high standard deviation can be considered as an indicator for unreliable water level which is better excluded for further application. Two problematic water levels showed high overestimation of the in-situ measurements, and they occurred at the lowest water level situations and during rainy season. The exact reason for such high overestimation needs to be investigated in the future study.