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Drought is defined as inadequate soil moisture to support crop growth and normal yield. The degree of drought for a given location depends on the crop, rainfall and its distribution, soil type, and various management practices. Drought occurs frequently in Tamilnadu—some part of the state experiences drought every year.
The state of Tamilnadu is located in the southernmost tip of peninsular India. It lies between 8°5" and 13°35" latitude north and 76°15" and 80°20" longitude east, covering an area of 0.13 million km2 and including a long coastline (about 1,000 km). The mean annual rainfall is 945 mm, with 45 rainy days. The state benefits from northeast monsoon rains (October– December), unlike other parts of India, where southwest monsoons (June– September) bring more rain. In Tamilnadu, 85% of the total area benefits from the northeast monsoon; only 15% benefits from the southwest monsoon. Potential evaporation always exceeds rainfall in most (8-10) months each year. The severity of drought depends on the type of soil prevalent in a region. It was once thought that farmers, through generations of experience, could learn to live with the limitations of their local climatic conditions through trial and error. That is no longer true. Modern agriculture requires precise information on rainfall and on flood- and drought-prone areas. It is now clear that to obtain maximum yields, a proper knowledge of agroclimatic conditions is necessary to plan the most effective cropping system for different areas. With this idea in mind, the state of Tamilnadu has been classified into drought-prone areas, based on precipitation, potential evaporation, and soil type, so that a suitable crop plan may be developed for each area.