National Aeronautics and Space Administration

Global reservoir information can not only benefit local water management, but can also improve our understanding of the hydrological cycle. This information includes water area, elevation, storage; evaporation rate and volume values; and other characteristics. However, operational wall-to-wall reservoir storage and evaporation monitoring information are lacking on a global scale. Here we introduce NASA's new MODIS/VIIRS Global Water Reservoir Product suite (https://modis-land.gsfc.nasa.gov/modgwr.html) based on moderate resolution remote sensing data-the Moderate Resolution Imaging Spectroradiometer (MODIS), and the Visible Infrared Imaging Radiometer Suite (VIIRS). This product consists of 8-day (MxD28C2 and VNP28C2) and monthly (MxD28C3 and VNP28C3) measurements for 164 large reservoirs. The 8-day product provides area, elevation, and storage values; which were generated by first extracting water areas from surface reflectance data, and then applying the area estimations to the pre-established Area-Elevation (A-E) relationships. These values were then further aggregated to monthly, with the evaporation rate and volume information added. The evaporation rate and volume information were calculated after the Lake Temperature and Evaporation Model (LTEM) using MODIS/VIIRS land surface temperature product and meteorological data from Global Land Data Assimilation System (GLDAS). Validation results show that the 250-m area classifications from MODIS agree well with the high-resolution classifications from Landsat (R² = 0.99). Validation of elevation and storage products for twelve Indian reservoirs show good agreement in terms of R² values (0.71-0.96 for elevation, and 0.79-0.96 for storage) and normalized root-mean-square error (NRMSE) values (5.08%-19.34% for elevation, and 6.39%-18.77% for storage). The evaporation rate results for two reservoirs (Lake Nasser and Lake Mead) agree well with in situ measurements (R² values of 0.61 and 0.66, and NRMSE values of 16.25% and 21.76%). Furthermore, preliminary results from the VIIRS reservoir product have shown good consistency with the MODIS based product, confirming the continuity of this 20-year product suite. This new global water reservoir product suite can provide valuable information with regard to water sources related studies, applications, management, and hydrological modeling and change analysis such as drought monitoring.