The Ganga-Bramhaputra Basin together store around 960 cubic km of water, researchers have claimed in a first of its kind study after mapping the rivers, and said it will help understand signatures of droughts and floods to better manage water resources in the region.
Scientists from India, the UK, France and Bangladesh undertook mapping of the two rivers during 2003 to 2007 from the basins with the help of satellite images.
"We estimated an annual variation of 410 cubic km for surface water and 550 cubic km for soil water. This study is the first of its kind as these estimates have never before been calculated for the Ganges-Brahmaputra Basin", researcher Fabrice Papa said.
Papa is from the Indo-French Cell for Water Sciences, a joint International Laboratory between the Bangalore-based Indian Institute of Science (IISc) and the Institut de Recherche pour le Development (IRD) in France.
The research also said that 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 per cent deficit in water storage in the basin when compared to that of the other years," Papa was quoted as saying by Gubbi Labs.
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.
The study was aimed at understanding the relationship between these elements by quantifying water storage at different levels, and variations across years.
For this the researchers used satellites Gravity Recovery and Climate Experiment (GRACE), Envisat and studied the rivers right from its origin to its mouth that gave them a bird's 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," said V Venugopal, Professor with the Centre of Atmospheric and Oceanic Sciences at the IISc.
"Since in situ observations are more accurate, we used them as a frame of reference for validation," Venugopal added. In this study, in situ (field) observations were acquired from Bangladesh.
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.
