Pointing to the Indus Water Treaty, Karnataka signals intention to review Cauvery water allocation

Aerial drone view of water being released from Mukkombu Upper Anaicut Dam into the Cauvery River. File | Photo credit: ANI

The state of Karnataka on Wednesday (Oct 7, 2026) signaled its intention in the Supreme Court to unravel the decades-old judicial consensus in the Cauvery water-sharing dispute on the grounds of “unfair allocation” of water and “changed circumstances”.

Even the Union of India has sought modification of the now shelved Indus Waters Treaty of 1960 based on changed circumstances, the state said.

Karnataka was responding to Tamil Nadu’s petition in the Supreme Court, complaining of backlogs in the allocation of Cauvery water.

The state’s response, filed by advocate Nishanth Patil and argued by senior advocate Mohan Katarki, referred to the international practice of reassessing interstate water allocations based on agreement or court order under changed circumstances, known as rebus sic stantibus.

“In view of the impending injustice, the State of Karnataka reserves the right to apply in changed circumstances for reopening of the unfair allocation in the tribunal’s award read with the judgment of the Supreme Court. It is normal practice that water allocations are reviewed periodically,” the 40-page reply said.

The tribunal’s decision along with the Supreme Court judgment in 2018 allocated the total annual flow of the Cauvery basin estimated at 740 tmc ft (thousand million cubic feet) at 50% confidence in the Lower Coleroon Anicut. This water was divided between Karnataka (284.75 tmc ft), Tamil Nadu (404.25 tmc ft), Keralam (30 tmc ft) and Puducherry (7 tmc ft), along with allocations of 10 tmc ft for environmental flows and 4 reserved in

In case the annual yield was less than 740 tmc ft in any water year due to hardship due to less rainfall, states were directed to share the problem proportionately (pro rata).

But Karnataka said there is no scientific formula for sharing anxiety pro rata or proportionately.

The current water year 2026-27 has been difficult due to failure of southwest monsoon from June to September. Water sharing was entirely based on a sense of justice, but hydrological realities have changed due to climate change, environmental degradation, shifting monsoons, etc. The water allocation and quantities decided by the tribunal and upheld by the Supreme Court followed a fixed pattern that did not take into account any of these subsequent developments, Karnataka’s reply said.

Water sharing in an emergency year must take into account the absence of a scientific formula for an emergency “as admitted by Tamil Nadu”. Secondly, the absence of a monthly component of the annual yield of 740 tmc ft was also a factor, the reply said.

In addition, the Cauvery basin has two rainy seasons: the southwest monsoon from June to September and the northeast monsoon from October to December or beyond. The northeasterly rains are mainly benefiting the lower coastal state of Tamil Nadu, while the failure of the earlier monsoon session has left Karnataka in dire straits.

Again, the reply said that Tamil Nadu was allotted the lion’s share of 404.25 tmc ft due to its claim of historic irrigation, while Karnataka State was allotted only 284.75 tmc ft of the 483 tmc ft available for Biligundla, ignoring its drought-prone areas.

“In a year of water scarcity, drinking water requirements should be the first priority as people cannot live without drinking water. Second priority must be given to dry irrigation in drought areas as irrigation in these drought areas provides minimal income and livelihood to farmers. Out of the current supply of 48,878 tmc ft in the remaining 5 drinking water reservoirs in Karnataka, there are four remaining drinking water supplies. 13,878 tmc ft are totally inadequate to cover dryland irrigation in the command of four reservoirs in Karnataka,” the state’s reply said.

Published – 7 Oct 2026 22:43 IST