Long-term total water storage change from a Satellite Water Cycle reconstruction over large southern Asian basins

The total water storage change (TWSC) over land is a major component of the global water cycle, with a large influence on the climate variability, sea level budget and water resource availability for human life. Its first estimates at a large scale were made available with GRACE (Gravity Recovery and Climate Experiment) observations for the 2002-2016 period, followed since 2018 by the launch of the GRACE-FO (Follow-On) mission. In this paper, using an approach based on the water mass conservation rule, we propose to merge satellite-based observations of precipitation and evapotranspiration with in situ river discharge measurements to estimate TWSC over longer time periods (typically from 1980 to 2016), compatible with climate studies. We performed this task over five major Asian basins, subject to both large climate variability and strong anthropogenic pressure for water resources and for which long-term records of in situ discharge measurements are available. Our Satellite Water Cycle (SAWC) reconstruction provides TWSC estimates very coherent in terms of seasonal and interannual variations with independent sources of information such as (1) TWSC GRACE-derived observations (over the 2002-2015 period), (2) ISBA-CTRIP (Interactions between Soil, Biosphere and Atmosphere CNRM - Centre National de Recherches Meteorologiques - Total Runoff Integrating Pathways) model simulations (1980-2015) and (3) the multi-satellite inundation extent (1993-2007). This analysis shows the advantages of the use of multiple satellite-derived datasets along with in situ data to perform a hydro- logically coherent reconstruction of a missing water component estimate. It provides a new critical source of information for the long-term monitoring of TWSC and to better understand its critical role in the global and terrestrial water cycle