Dr Alexander Densmore reports from northwestern India on a new project funded by the NERC Changing Water Cycle programme that investigates the effects of past, present and future climate on groundwater systems in this part of the world.
Northwestern India is the country’s breadbasket. The plains of Punjab and Haryana now produce most of the nation’s wheat and rice due to a focused programme of agricultural growth over the last few decades. The semi-arid climate and highly seasonal monsoon precipitation, however, mean that this lush productivity comes at a cost. Northwestern India is also one of the world’s worst ‘hotspots’ of groundwater depletion –- in other words, groundwater is being extracted from the subsurface at a far higher rate than it is being recharged by precipitation and river flow. A key regional-scale study using GRACE satellite data, published by Rodell et al. in Nature in 2009 (‘Satellite-based estimates of groundwater depletion in India‘), showed that across the states of Punjab, Haryana, and Rajasthan, groundwater was lost at a rate of more than 50 km3 per year from 2002 to 2008. This unsustainable deficit poses a grave threat to the continued development of the region, home to more than 100 million people. What’s more, there are indications from regional-scale climate modelling that climate change over the next 30-50 years is likely to decrease summer monsoon precipitation and delay its onset, in precisely the regions that are worst affected by groundwater depletion.
To begin to understand this issue, we are starting a new research project on the aquifer systems of northwestern India, funded by the UK National Environmental Research Council and the Indian Ministry of Earth Sciences. I am working with researchers from the Indian Institute of Technology Kanpur, Delhi University, the National Institute of Hydrology in Roorkee and Imperial College London.
We have spent the last few days in rural Punjab state examining the basin of the Ghaggar River –- an area that we think is a model example of the sort of aquifer that must be understood, and characterised, to help us forecast the response of the groundwater system to climate change. In contrast to its larger brethren like the Ganga, Sutlej, and Yamuna Rivers, the Ghaggar River is relatively small by Himalayan standards. It rises in the Himalayan foothills and enters the Indo-Gangetic Plains near the city of Chandigarh, meandering its way across three states before ultimately discharging into the Sutlej River in eastern Pakistan. Because it is not fed by snow and ice, its runoff is highly dependent on monsoon precipitation, and it varies from a 10-m deep torrent in August to a trickle by early March:
Because the river flow is so variable, farmers in the area rely on groundwater for irrigation. This groundwater is extracted from thousands of shallow wells that dot the northwestern Indian plains. Many of these wells were initially drilled to depths of 10-20 m and operated by small petrol-powered pumps, like this one:
Continued extraction, however, has lowered the groundwater table locally by many tens of meters, necessitating the use of submersible electric pumps. These pumps, running 24 hours a day on free (state-subsidised) electricity, can extract 10-20 litres per second from depths of more than 100 m.
Farmers in the area have watched the decline in groundwater levels for years and are deeply concerned about its effect on their livelihoods. They understand both the severity of the problem and its multiple causes. Some of the measures intended to alleviate water issues have, paradoxically, made the problem worse. One farmer near Patran told us that a nearby canal, built in the 1950s to transfer water between states, is now so leaky that it prevents the monsoon floods on the Ghaggar from recharging the groundwater, and thus raises the level of the flood peaks. ‘The canal is a big problem for us’, he said. As the farmers drill ever-deeper wells (and install ever-larger pumps) to mine the dwindling supply of groundwater, the water in the canal keeps rushing southwards destined eventually to evaporate from the arid fields of Rajasthan.