Tamil Nadu's granary losing substantial ground: delta region shrinks by 20% -Vidya Venkat

-The Hindu

Climate change and anthropogenic factors are having a detrimental effect on the Cauvery delta region, a study spanning almost four decades reveals

The Cauvery delta region, widely regarded as the granary of Tamil Nadu, has shrunk, with cultivable lands increasingly deteriorating into waste lands — this is the finding of a recently concluded study undertaken by retired professor of the Madras Institute of Development Studies (MIDS) S. Janakarajan.

Funded by the Indian Council of Social Science Research (ICSSR), the study was conducted between 2014 and 2016 and covers a period spanning almost four decades, beginning from the 1970s. Through the comparison of the geographic information system (GIS) imagery for May 2014 with the 1971 toposheet obtained from the National Remote Sensing Centre at the Indian Space Research Organisation (ISRO), the researcher has tracked land use and changes to land cover to show that the delta region has shrunk by 20% due to anthropogenic factors such as diversion of land for non-agricultural purposes, as well as factors linked to climate change.

For a once-prosperous agricultural belt, the drastic reduction in crop cover and a 13-fold increase in wastelands between 1971 and 2014 indicate a worrisome phenomenon. “Much of this is because the land is kept fallow due to lack of water and other adverse climatic conditions,” Mr. Janakarajan says.

Risk of sinking

Another phenomenon reported by the study is the increase in mangrove cover in the region as sea water ingress has grown in the coastal areas. The data shows that mangrove cover has gone up nearly 14 times since 1971.

“Increasing mangrove cover is nothing to be happy about, because what that means is that more and more cultivable agricultural land is coming under sea water and the soil is turning saline,” Mr. Janakarajan says. With 72% of the low-lying land in the State falling under the delta region along the coast, the land in this region is at greater risk of submergence as a result of rising sea levels due to climate change. The author cites studies by Sujatha Byravan and others to show how a substantial portion of land in the delta region is at an elevation of merely a metre from the sea. He raises the issue of reduced sediment flow to the delta, which otherwise helps maintain the critical elevation level from the sea.

“There is an almost near-unanimity among researchers that the withholding of the river flow upstream through the construction of a series of dams is the fundamental reason for the reduced or no sediment flow downstream, and that delta subsidence [ Imminent threat to coastal populations] is in a large measure attributable to these kinds of human intervention in the rivers,” Mr. Janakarajan says, pointing out that the Cauvery delta has witnessed a decline of 80% in sediment deposit over the last century.

This is borne out by the loss of storage capacity in the Mettur dam as a result of siltation, for instance. The dam, constructed in 1934, used to have a storage capacity of 2708.8 million cubic metres (MCM). By 2004, this was reduced to 1994.2 MCM. Besides, data reveal that its capacity had reduced further to 1,889 MCM in 2015. Sediment flow to the Cauvery delta has been practically nil of late, as per a 2015 report by the Central Water Commission cited by the study.

Cycle of drought and flood

A noticeable consequence of climate change has been the cycle of drought and flood that coastal areas have been enduring. While there has been a decline in the overall rainfall between 1974 and 2004, the study reports an increase in rainfall, occurring in spurts, at the local level. The overall decline in rainfall has not been borne out across the Cauvery basin in the State. During several years, the delta districts received 1,200 mm of rainfall, which is high. However, this pattern has not spread out. Usually, the rain occurs within a span of a few days, resulting in heavy flooding. The fields get flooded and the crops are destroyed. On the other hand, there is the prevalence of droughts such as the one that the State is currently reeling under.

All these factors have resulted in a drastic reduction in land under crop cover to the tune of 27%, as against 1971 levels. Due to sea water ingress, there has been a substantial rise in shrimp farming along the coast, which is detrimental to agricultural practice, the author points out.

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The Hindu, 15 July, 2017, http://www.thehindu.com/news/national/tamil-nadu/states-granary-losing-substantial-ground/article19286764.ece

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