"90 percent of Karnataka’s subdivisions of districts recorded deficit rainfall in August."
"Karnataka was 16 percent short of normal rainfall between 1 June and 5 September, 2016."
"Karnataka’s four zones — south and north interior, the southern Malnad region and the coast — recorded a 39 percent deficit in rainfall."
According to a report in The Economic Times report, Karnataka has 35 tmcft of water in four reservoirs as compared to Tamil Nadu which has 49 tmcft in two reservoirs.
The Indian Express also reported that the deficiency “meant that the four reservoirs in the Cauvery basin in Karnataka — Krishnaraja Sagar, Harangi, Hemavathi and Kabini — have together received only 114.66 thousand million cubic (tmc) ft of water until the end of August, about half the normal 215.70 tmc ft.”
The government of Tamil Nadu approached the Supreme Court to secure the interests of its farmers in the Thanjavur region, who mostly grow paddy from August to January, said The Indian Express report.
Paddy, according to an ORF report, is a major cause for the water dispute. Besides it being a water-intensive crop, growing paddy means incentivisation for farmers from the government — so much so that farmers in both sides of the dispute grow it. In Tamil Nadu, paddy fields are grown downstream, which means that it requires a lot of water, according to this report in The Caravan that also added that Karnataka farmers are deserting sugarcane farming and taking to paddy cultivation (when compared to sugarcane, paddy utilises less water)
According to The Hindu’s report, the average drop in ground water across Tamil Nadu has been 0.34 metres/year in the past five years. The report estimates that such an alarming rate of depletion may be because of the state’s agricultural practices. Of all the sown land in the state, almost 32 percent is sown with rice. Look at it from another angle, almost 12 percent of the state’s total area is just rice crop.
Rice crop is extremely sensitive to water shortages. Farmers usually aim to have flooded conditions in their field to ensure the cultivation of the crop.
TS Sudhir argues in this Firstpost article, "The samba crop (a form of paddy) is spread over four to five months, from September to January and needs at least 90 tmc feet of water." He further quotes a farmer as saying that the delta soil cannot be used to grow millets and there is no other option but to grow paddy.
The aforementioned ORF report also said that with PDS selling rice at a lower price than other crops, the demand for it becomes high, thanks to its consumption as well. And so, water for irrigation becomes an issue. Unless the political class in Tamil Nadu finds a better way to manage water and crop patterns — or employing the resources it has such as ground water — the situation will be till then locked in an impasse.