Abstract
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, and storage; evaporation rate and volume values; and other characteristics. However, operational wall-to-wall reservoir storage and evaporation monitoring information is lacking on a global scale. Here we introduce NASA’s new MODIS/VIIRS Global Water Reservoir product suite 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 (MxD stands for the product from both Terra (MOD) or Aqua (MYD) satellites). 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 values were calculated after the Lake Temperature and Evaporation Model (LTEM) using MODIS/VIIRS land surface temperature product and meteorological data from the 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.
Highlights
IntroductionReservoirs serve as a lifeline in water management (e.g., irrigation, hydropower generation, water supply, and flood control), especially under the ongoing fast population growth and changing climate [1,2,3,4,5]
Reservoirs serve as a lifeline in water management, especially under the ongoing fast population growth and changing climate [1,2,3,4,5]
Detailed descriptions of all of the algorithms involved in the product’s development (e.g., the enhancement water of the algorithms involved in the product’s development are provided in the classification algorithm and evaporation rate estimation algorithm) are provided in the Algorithm Theoretical Basis Documentation (ATBD) [41], which is available through the Algorithm Theoretical Basis Documentation (ATBD) [41], which is available through the product website
Summary
Reservoirs serve as a lifeline in water management (e.g., irrigation, hydropower generation, water supply, and flood control), especially under the ongoing fast population growth and changing climate [1,2,3,4,5]. Reservoirs supply about 40% of the total irrigation water demand [1] and contribute to more than 60% of renewable energy via hydroelectricity [6]. Reservoir storage varies according to natural climate variability as well as the human water use/demand for different sectors (i.e., domestic, agricultural, and industrial). Long-term records of water retained by global reservoirs can help to evaluate the human impacts on global and regional water cycles [9,10]. Because gauge observations for reservoir storage (and/or elevation) are typically not shared, both of the aforementioned data needs are difficult to satisfy at regional and global scales
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