The Ganges River is one of the largest rivers in the world and one of the most threatened. The Ganges-Brahmaputra basin is the largest in India; it contributes approximately 59 per cent of the water resources used in the country. Pollution and increasing water consumption, mainly for use in agriculture and energy production, are the two largest challenges to the river.
India is the largest consumer of groundwater in the world; it consumes over a quarter of the global total – equivalent to 230,000 gigalitres per year. Most groundwater is used for agricultural irrigation, which accounts for 88 per cent of total Indian groundwater usage. The World Bank predicts that by 2032, almost two-thirds of the aquifers in the country will be in a critical state; which will undermine agricultural production in regions that depend on groundwater. A new analysis of the interaction between ground and surface water in the lower reaches of the Ganges River basin, however, indicates that it will also affect surface water supplies.
In the lower reaches of the Ganges River, water loss is particularly evident during the summer months, ahead of the annual monsoon. Water levels were estimated at a number of locations between the city of Varanasi, in Uttar Pradesh, and the city of Kolkata, on the Bay of Bengal.
The estimates are based on both satellite data and numerical models. They suggest that since the 1970s, when electric- or diesel-powered irrigation technology was first introduced in India, the summer flow of the river has decreased by almost 60 per cent in parts of its lower reaches.
Aquifers supplement the Ganges during the dry summer. During those pre-monsoon months, groundwater contributes up to 70 per cent of the water in some sections of the river. Surface water, which is mainly derived from rains associated with the monsoon, accounts for most of the water in the river during the monsoon months (June-September). As the aquifers that would normally augment the surface water supply in the summer are increasingly overexploited, they contribute less water to the river than in previous decades. According to the results of the analysis, the proportion of groundwater entering the Ganges in its lower reaches has decreased by about 59 per cent since 1970.
The analysis does not take climate change into account. It does, however, note that the amount of rain falling in the lower reaches of the Ganges River has increased since the 1970s. It is, therefore, unlikely that the drier conditions are directly caused by climate change. Climate change is expected to have a limited effect on the Ganges as a whole. Its upper reaches are more likely to be affected by a reduction in the amount of meltwater flowing into the river from glaciers and snow. Glacial meltwater makes up less than ten per cent of the river’s total volume, however, and even in the upper reaches of the river, most of its water comes from precipitation associated with the monsoon. Groundwater gain or loss is likely to have a larger effect on the water level of the Ganges than climate change.
Surface water accounts for 27 per cent of the irrigation water used in the study area. If the water level in the region continues to decline, more pressure will be put on groundwater resources and food production. The researchers estimate that if current trends continue, water stress in the lower reaches of the river will continue to rise, leading to a reduction in food security for 115 million people.
Upmanu Lall, the Director of the Columbia Water Center, suggests that the food production systems in the lower Ganges River underperform when compared to other regions of India. He stated that ‘the crop yields are actually quite low and less than 50% of the yields for rice and wheat in the top producing Indian states’. That suggests that farmers in the lower reaches of the Ganges River are using a lot of water for very limited results. Finding ways to improve water utilisation (“growing more crop per drop”) will help to alleviate the strain on water resources and reduce water stress, while still protecting food security. Another option proposed in the analysis, is to actively manage aquifers in the Ganges basin. That would involve recharging overexploited aquifers with rainwater or diverted surface water.
Water levels in the Ganges River are most likely to be affected by increased groundwater use and changes to rainfall patterns. A reduction in meltwater from glaciers and snow in the Himalayas could reduce water levels in the upper reaches of the river, but even here it is more likely that changes in precipitation will have a larger effect. To avoid increasing food and water insecurity levels, water needs to be better utilised and managed.