Performance Analysis of Satellite Altimetry Missions in Water Level Retrieval and Drought Detection: A Case Study in Iran

Abstract Satellite altimetry is a key method for monitoring water level, analyzing variations from intraseasonal to interannual scales, and aiding drought monitoring in watersheds. Radio detection and ranging (RADAR) altimetry has been employed to determine water surface elevations, yet assessing the accuracy of satellite RADAR altimetry in specific regions remains important. This research focuses on validating water level time series derived from satellite altimetry and on exploring their usefulness for drought detection. Afterward, the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI) were used to analyze the relationships between satellite altimetry-measured water level changes and drought occurrence. Water level time series from environmental satellite (Envisat), satellite with ARgos and ALtiKa (SARAL), Sentinel-3A, Sentinel-3B, The Joint Altimetry Satellite Oceanography Network (JASON) series were extracted and compared with observed daily water levels for eight water bodies in Iran between 2000 and 2022. Results showed lower root mean square error (RMSE) values (0.04 and 0.07 m) for SARAL and Sentinel-3A, respectively, and higher R-squared ( R 2 ) values (0.98 and 0.97) for Sentinel-3A and SARAL, respectively. Subsequently, the SPI and the SPEI were used to analyze relationships between satellite altimetry-measured water-level changes and drought occurrence, SPI and SPEI trends, and the capability of SPI and SPEI in monitoring drought events. Results showed that the Envisat altimetry mission at Zarivar Lake performed optimally, with an average probable drought detection of 73% in detecting mild drought conditions. Overall, this research has demonstrated that satellite altimetry data can monitor water-level changes for drought assessment.