Tamil Nadu's grasslands are key to water security:

Reality check

by Gopikrishna Warrier

The India Meteorological Department (IMD) has downgraded its forecast for the southwest monsoon for 2015 to 86% of the average.

Grasslands are critical to water security in Tamil Nadu(travelblog.org)

Many times, forecast of deficient rains has later turned out to be incorrect. But, irrespective of whether the forecast proves right or not this year, long-term data does show that southwest monsoon has been decreasing in Tamil Nadu over the years, which doesn't bode well for the rivers in the state.

The commonly held belief that the southwest monsoon is not very important for the state's economy is incorrect. The state has to immediately ramp up its conservation strategy to counter the effects of climate change. It has to take steps to protect the biological diversity and biological wealth at the points from where the perennial rivers in the state originate.

It is true that as the monsoon clouds, heavy with rain, move eastwards from Kerala, the tall ridges of the Western Ghats block them. But the Palghat Gap and the gap across the Periyar Tiger Reserve are gateways that allow the rain bearing clouds into districts like Nilgiris, Erode, Coimbatore, Tirupur and Theni. The IMD figures for Tamil Nadu and Puducherry state that while on an average the southwest monsoon contributes 321.4 mm of rainfall, the northeast contributes 442 mm.

It is often forgotten that the water carried by the river s flowing through the state is as important as the rain important as the rain that falls on the land. And this is where the southwest monsoon has a disproportionate impact on Tamil Nadu.

There are only a few rivers in the state that flow throughout the year and these rivers originate from the Western Ghats that are fed in good measure by the southwest monsoon. It is the biological health of the catchment (the area where the rain water falls) that determines whether a river will be seasonal (have water flowing only during the rainy months) or perennial (have water throughout the year). Thus, Cauvery and Thamirabarani rivers originating from the biologically-rich catchments in the Western Ghats are perennial, while Palar and Ponnaiyar rivers originating from the drier Eastern Ghats are seasonal.

The rivers originating from the upper plateaus of the Western Ghats get their water from the unique shola-grassland ecosystem.

This is a combination This is a combination where the ridges are covered with grasslands and in the fold of the valleys there are thick montane, evergreen (shola) forests.

Over millennia, the leaves that fall on the forest floor have got swept into the bottom of the rivulets where they have decayed and turned into peat. While the grasslands let the rainwater runoff into the forest floor, the peat bogs store it and release it slowly into the rivulets all through the year.

Of the four rivers that arise from the Nilgiris ?¡ Bhavani, Moyar, Kabini and Chaliyar ?¡ the first three flow east and join the Cauvery. The Mukurthi ridge, from where Bhavani originates, has among the highest annual precipitation in Tamil Nadu ?¡ more than 5,000 mm, largely from southwest monsoon. For Tamil Nadu, protecting the health of the shola-grassland ecosystem and the other forests in the catchment would mean protecting the source of water flowing through the perennial rivers.

According to IMD's analysis of longitudinal climate data for 59 years from 1951 to 2010, Tamil Nadu has already started feeling the impact of climate change. This is both in terms of increase in annual temperature and decrease in annual rainfall during the southwest monsoon. The state's mean annual temperature increased by 0.02??Cyear over this period. Further, the mean maximum temperature increased by 0.03??Cyear. As regards rainfall, though the annual mean rainfall increased by 0.8 mmyear, the rainfall during the southwest monsoon decreased by 1.35 mm year. On the other hand, the rainfall during the no southwest monsoon period increased by 1.49 mm year.

Over the years, TN has been getting warmer, and the hot days are becoming hotter. Though the annual rainfall has increased, this has come from more rains during the non-southwest monsoon period, which for the state is predominantly the northeast monsoon and other cyclonic events. The southwest monsoon provides a steady rainfall pattern and is good for farming. Rain in other parts of the year comes in short, heavy bursts and sometimes in cyclonic storms, which is not always good for farmers. The Intergovernmental Panel on Climate Change (IPCC) predicts that such extreme weather events are only likely to increase in the future.

-Times of India