Impact of transient groundwater storage on the discharge of Himalayan rivers

• Published in: Nature geoscience Vol. 5; no. 2; pp. 127 - 132
• Main Authors: Andermann, Christoff, Longuevergne, Laurent, Bonnet, Stéphane, Crave, Alain, Davy, Philippe, Gloaguen, Richard
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.02.2012; Nature Publishing Group
• Subjects: 704/2151/241; Basins; Catchments; Continental interfaces, environment; Earth and Environmental Science; Earth science; Earth Sciences; Earth System Sciences; Environmental Sciences; Evapotranspiration; Freshwater; Geochemistry; Geology; Geophysics/Geodesy; Glaciers; Global Changes; Groundwater; Groundwater storage; Hydrology; letter; Precipitation; Reservoirs; River discharge; River flow; Rivers; Sciences of the Universe; Snow; Storage capacity; Water budget; Himalaya Mountains; France; Nepal; Pakistan, Himalayas
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/ngeo1356

In the course of the transfer of precipitation into rivers, water is temporarily stored in reservoirs with different residence times. Analyses of precipitation and discharge records from Nepal suggest that in addition to snow and glacier melt and evapotranspiration, groundwater storage in a fractured basement aquifer also affects the annual discharge cycle of Himalayan rivers. In the course of the transfer of precipitation into rivers, water is temporarily stored in reservoirs with different residence times 1 , 2 such as soils, groundwater, snow and glaciers. In the central Himalaya, the water budget is thought to be primarily controlled by monsoon rainfall, snow and glacier melt 3 , 4 , and secondarily by evapotranspiration 3 . An additional contribution from deep groundwater 5 , 6 , 7 has been deduced from the chemistry of Himalayan rivers 6 , but its importance in the annual water budget remains to be evaluated. Here we analyse records of daily precipitation and discharge within twelve catchments in Nepal over about 30 years. We observe annual hysteresis loops—that is, a time lag between precipitation and discharge—in both glaciated and unglaciated catchments and independent of the geological setting. We infer that water is stored temporarily in a reservoir with characteristic response time of about 45 days, suggesting a diffusivity typical of fractured basement aquifers 8 . We estimate this transient storage capacity at about 28 km 3 for the three main Nepal catchments; snow and glacier melt contribute around 14 km 3  yr −1 , about 10% of the annual river discharge. We conclude that groundwater storage in a fractured basement influences significantly the Himalayan river discharge cycle.