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How much water does the Ganges-Brahmaputra basin store?

An international team of scientists from India, Bangladesh, France and UK has mapped for the first time, the amount of fresh water stored in the Ganges-Brahmaputra basin of the Indian sub-continent.

The Ganges-Brahmaputra basin covers a large area, extending over India, Nepal, Bhutan, China and Bangladesh. The basin houses rivers, floodplains, lakes, wetlands and the largest delta in world, all of which contribute significantly to the regional climate; groundwater, surface water and rainfall form an interconnected cycle and are constantly affecting each other. This study was aimed at understanding the relationship between these elements by quantifying water storage at different levels, and variations across years.

With the increasing pressure on water resources that leads to groundwater depletion in the region, it is crucial to estimate the actual availability of water in large rivers of the Indian subcontinent. Quantifying this gives scientists new insights in understanding the variations that are occurring either due to climatic or developmental changes.

To acquire an accurate estimate of water availability, the researchers employed a multi-satellite technique that gave them a birds-eye-view. “With in situ observations, it is difficult to study large areas as measurements are done at single points. A multi-satellite approach gives us a better understanding of the spatial variation of water-related observables,” explains Prof V. Venugopal from the Centre of Atmospheric and Oceanic Sciences, IISc. “Since in situ observations are more accurate, we used them as a frame of reference for validation.” In this study, in situ (field) observations were acquired from Bangladesh.

The researchers studied the variations of freshwater storedin the Ganges-Brahmaputra basin during the period 2003-2007. From the values of total water storage and surface water storage, they derived the changes in sub-surface water availability. “We estimated an annual variation of 410 km3 for surface water and 550 km3 for soil water. This study is the first of its kind as these estimates have never before been calculated for the Ganges-Brahmaputra basin”, says Dr. Fabrice Papa from the Indo-French Cell for Water Sciences, a joint International Laboratory between IISc and the Institut de Recherche pour le Development (IRD) in France. Both surface and sub-surface water storage also show strong year to year variability. During the monsoon of 2006, which can be considered as a drought year, there was found to be a 30% deficit in water storage in the basin when compared to that of the other years.

The researchers believe that these new datasets will provide an opportunity to study the signatures of droughts and floods, and ultimately to help better manage water resources in the region. It will also help better understand the amount of freshwater entering the Bay of Bengal and the role it plays in regional sea-level rise. 

About the authors

The study was carried out by a multi-country, multi-institution team from India, France, Bangladesh and the UK.

First author Fabrice Papa is from the Institut de Recherche pour le Developpement, Toulouse, France
and the Indo-French Cell for Water Sciences, Indian Institute of Science, Bangalore, India.

Co-authors from IISc:

Venugopal Vuruputur is from the Centre for Atmospheric and Oceanic  Sciences and the Divecha Centre for Climate Change, both at Indian Institute of Science, Bangalore, India. Muddu Sekhar is from Department of Civil Engineering and IFCWS, Indo-French Cell for Water Sciences, IISc.

Venugopal Vuruputur: http://caos.iisc.ernet.in/faculty/venu.html

E-mail: venu@caos.iisc.ernet.in; Tel.: +91-80-2293-3073

Fabrice Papa: fabrice.papa@ird.fr

About the paper

The paper appeared in the Journal of Hydrology: Regional Studies
last month. http://www.sciencedirect.com/science/article/pii/S2214581815000221