Coherent Satellite Monitoring of the Water Cycle Over the Amazon. Part 1: Methodology and Initial Evaluation.

Monitoring coherently the Amazon Water Cycle (WC) using satellite observations is crucial for climate and water resources studies. The SAtellite Water Cycle (SAWC) integration methodology is introduced to optimize the satellite datasets. In this paper, the WC budget is balanced simultaneously over 10 sub‐basins by constraining the horizontal water exchanges between them. Compared to an actual assimilation analysis, SAWC benefits from the use of water storage observations from Gravity Recovery and Climate Experiment. SAWC corrects the satellite evapotranspiration datasets that tend to under‐estimate the water‐limited evaporation over the central Amazon and to over‐estimate the energy‐limited evaporation over the northern Amazon. The SAWC precipitation estimates are evaluated against gauge measurements and show good overall results with a correlation varying from 0.94 to 0.99 and root‐mean‐square deviation between 16 and 41 mm/month (≃10% of precipitation estimate). Plain Language Summary: The Amazon basin is the major hydrological basin on Earth, but quantifying its various water stocks and fluxes by using satellite observation remains a true challenge. In order to obtain a better description of the water cycle, we propose here a new methodology that optimizes all the available satellite estimations. Compared to previous efforts, river discharge measurements are used to constrain the horizontal water exchanges among the sub‐basins. This methodology allows obtaining a more accurate and coherent quantification of the water cycle, at the regional scale. The optimized rainfall estimates show improvement compared to original datasets when evaluated against gauge measurements. The methodology corrects also the evapotranspiration season estimate that tends to under‐estimate the water‐limited evaporation over the central Amazon and to over‐estimate the energy‐limited evaporation over the northern Amazon. Key Points: A satellite‐data integration technique can exploit the water budget closure and water exchange between the sub‐basinsSatellite‐based precipitation data set is improved compared to in situ gaugesThe evapotranspiration estimates are improved by stressing the water or energy limitation regime over the amazon [ABSTRACT FROM AUTHOR]