Rivers are losing water for many reasons. The biggest loss comes from water used for irrigation. This water is consumed by crops and also lost in evaporation.
The next loss is due to the groundwater situation. India’s groundwater situation is growing dire. In 2011, almost 30% of India’s districts had a groundwater situation that was either semi-critical, critical or overexploited. This is up from just 8% in 1995. “If current trends continue, in 20 years about 60% of all India’s aquifers will be in a critical condition” says a World Bank report. When groundwater is over-extracted, this leads to a drop in the water table. The water in the river then seeps into the ground rather than groundwater feeding the river.
Additionally, when forest turns into cropland or wasteland, the soil does not absorb as much water from rain. So, rain that falls may evaporate directly from the land surface. A study in 2012 on a portion of the Varahi river in the Western Ghats found that even small changes in forest cover – 9% over 27 years – can reduce the buffering capacity of the river’s flow. The number of days the river flowed after cessation of rainfall reduced and the number of dry stream days increased.
Also, more water enters the river from flow over the land surface than through underground water. This reduces the perennial nature of the river and increase flood risks.
Extraction for domestic and industrial use in major rivers accounts for about 1% of the water volume. The final reason is change in rainfall, which varies from basin to basin.
Example: Changes in the Krishna River
Some figures can be found in an analysis done on the Krishna river comparing the situation between 1955-1965 and 1990-2000. Between 1955-1965, average flow of water into the sea was 67.3 cubic kms.. Between 1990-2000, the avg flow was 19 cubic kms, a reduction of 48.3 cubic kms. Of this, domestic consumption increased by 1.2 cubic kms. Rainfall decreased by 15.6 cubic kms. The underground baseflow into the river dropped by 10.5 cubic kms, mainly because groundwater pumping increased by 8.8 cubic kms. 27.3 cubic kms was due to increased consumption from irrigated crops. Though rainfed crops consumed more water than irrigated crops, the situation with rainfed crops did not change between these two time periods. Natural vegetation also stayed more or less the same.
Net irrigated area in the Krishna basin increased from 0.52 million hectares to 1.3 million hectares and average cropping intensity rose from 108 to 120%. In these areas, millets – which consume less water per kg of grain – were mainly replaced by rice and cash crops such as sugarcane and cotton.
Rice was the most commonly grown crop in irrigated areas. 84% of rice was cultivated with irrigation. 100% of the sugarcane was irrigated. About 25% of fruits were irrigated, though fruits were only grown on 2% of the agricultural land.