CoAuthors

Fabrice Papa (Institut de Recherche pour le Developpement, IRD, LEGOS, Toulouse, France and IFCWS, Indo-French Cell for Water Sciences, IRD-IISc Joint International Laboratory Indian Institute of Science, Bangalore, India, France); Frederic Frappart (Observatoire Midi-Pyrénées (OMP), GET, Toulouse & Observatoire Midi-Pyrénées (OMP), LEGOS, Toulouse, France); Florian Jordy (Universite de Toulouse; UPS, LEGOS, Toulouse, France); Vincent Marieu (Universite de Bordeaux ; EPOC, Bordeaux, France); Mohammad Shamsudduha (Institute for Risk and Disaster Reduction University College London, London, United Kingdom ); Venu Venugopal (Center for Oceanic and Atmospheric Sciences, Indian Institute of Science, Bangalore , India); Muddu Sekhar (Department of Civil Engineering and IFCWS, Indo-French Cell for Water Sciences, Indian Institute of Science, Bangalore, India); Guillaume Ramillien (CNRS, Geoscience Environement Toulouse, OMP-GET, Toulouse, France); Catherine Prigent (LERMA, CNRS, Observatoire de Paris, Paris, France); Filipe Aires (Estellus, Paris, France); Rajesh Kumar (Pandey NGRI, Hyderabad, India); Sujit Bala (Institute of Water and Flood Management Bangladesh University of Engineering and Technology, Dhaka, Bangladesh); Stephane Calmant (Institut de Recherche pour le Developpement, IRD-LEGOS, Toulouse, France)

Terrestrial water is critical to sustaining life on Earth and plays a primary role in the global water cycle and the global climate. However basic questions still remain open related to the land water budget such as: Where, how and why do the different components of the terrestrial water storage vary at time scales from a few days to years, from regional to continental and global scale?

We propose to work towards answering these crucial questions by combining surface water extent from a multi-satellite-technique (GIEMS) with altimeter-derived level variations (ENVISAT) of large surface water bodies to estimate surface freshwater storage (SWS) variations over the Ganges-Brahmaputra (GB) basin, the third largest freshwater outlet to the world's oceans. In addition to monsoons and strong climate variability, the GB basin is facing the growing demands for freshwater availability by a continually growing population (more than 700 millions people) and fast development of agricultural and industrial sectors. The management of water resources is then of highest priority and, in the context of current over-abstraction of groundwater, accurate observations of terrestrial freshwater storage and variability are essential.

For the very first time, monthly variations of surface water volume will be presented over 2003-2007 periods, showing a strong seasonal cycle and a substantial interannual variability. Over the basin, the results will be cross-checked and evaluated against related hydrological parameters (in-situ river discharge, rainfall data, etc). The basin-scale SWS mean annual amplitude of ~410 km3 contributes to about 45% of the Gravity Recovery And Climate Experiment (GRACE)-derived total water storage variations (TWS). During the drought-like conditions in 2006, we estimate that the SWS deficit over the entire GB basin in July-August-September was about 30% as compared to other years. Finally, the SWS variations are used to decompose the GB GRACE-derived TWS and to isolate the variations of subsurface water storage (SSWS, groundwater + soil moisture), which mean annual amplitude is estimated to be of ~550 km3. This new 5-year data set of SWS and SSWS variations represent an unprecedented source of information for hydrological or climate modeling studies of the Indian sub-continent. It is also a first step toward the development of such long-term database at continental and global scales. In addition, our results will help to validate/evaluate large-scale hydrological models and better prepare and validate future hydrology-oriented missions such as SWOT.

illustration legend : Global map of the annual maximum surface water extent (averaged over 1993-2007) derived from the multisatellite method.