Surplus river basins face drop in rainfall: IIT study

A study carried out by a team of researchers from IIT Madras and IIT Bombay has found a decrease in spatial variability of mean monsoon rainfall over major river basins in India.

While there is a statistically significant decrease in the monsoon rainfall over major water surplus river basins, there is no statistically significant increase in monsoon rainfall over major water deficit river basins.

Key Findings:

• Major surplus basins such as Mahanadi, Godavari, Brahmani and West Flow River-I are witnessing significant decrease in rainfall. Other surplus basins also exhibited decrease in rainfall but they are not statistically significant.
• The decrease in water yield in recent periods in major surplus basins has been more than 10 per cent in the case of Mahanadi and West Flow River-I. In the case of other surplus basins, the decrease has been within 10 per cent.
• Though water yields in major deficit river basins such as Indus, Ganga and East Flow River-II have increased during the period 1976-2000 compared with the previous 25 years (1951-1975), the trend is not statistically significant.
• Ganga, which is a major water deficit basin, has seen significant increase in rainfall, while Yamuna, Krishna and Cauvery river basins exhibit a decrease.
• There has been an increase in extreme rainfall events in India but this does not play a significant role in water availability as the surplus water gets wasted.
• The changes in rainfall pattern over major river basins in India raises concerns regarding the suitability and viability of interlinking major river water basins.
• The water demand in a surplus basin first needs to be assessed and then met under decreasing water availability scenarios before transferring water to deficit basins.

Hence, planning for inter-basin water transfer [in order to supply water from surplus to deficit river basins] necessitates an immediate reassessment with a systematic approach.