Rainfall as the principal parameter is the basis of all definitions on drought. According to IMD (1971), drought is said to have occured over a region when rainfall received is less than 75 per cent of the normal value of the region.

This degree of deficit is termed as moderate drought. When rainfall received is only 50 per cent of the normal, in that situation severe drought is said to have occurred. Thus rainfall deficiency of 28 to 50 per cent from normal over a meteorological sub-division is termed as moderate drought and a deficiency of more than 50 per cent of normal as severe drought.

Drought has been classified as of several types: Meteorological drought, hydrological drought, agricultural drought etc. Meteorological drought or flood, of which we are concerned at present, is defined as a phenomenon, which occurs when a region receives a lower or higher rainfall than the normal mean value of the region.

Many countries including USA and Australia use a given percentage departure from the normal as the definition of drought. For USA, Bates (1935) suggested that a region may be termed drought affected if its annual precipitation is not more than 75 per cent of its normal. For India deficit rainfall is not an uncommon occasion and it has constantly added pressure on our limited resources. Economic planning has been undertaken to mitigate its effect and often plans have failed as a result of it.

ADVERTISEMENTS:

Frequency of Droughts in India

On the basis of IMD classification, the drought events, which have occurred due to rainfall variability over the twenty-nine Indian meteorological sub-divisions, have been studied.

It depicts the frequency of drought occurrence over the twenty-nine meteorological sub­divisions. The frequency of occurrence of drought ranged from less than five to more than thirty times in the various meteorological sub-divisions.

The six sub-divisions of Eastern India have experienced least number of drought events. On the other hand, the three extreme western meteorological sub-divisions of Western Rajasthan, Saurashtra-Kutch and Punjab have experienced the most number of drought occurrences and are of moderate intensity.

ADVERTISEMENTS:

Only thirteen (13) of the twenty-nine meteorological sub-divisions have faced severe drought during the past 110 years. Among these, incidences of severe drought has been maximum in Eastern and Western Rajasthan, Gujarat plains, Saurashtra-Kutch and Marathwada.

Occurrence of Droughts

As many as 99 districts, spread over 14 states, were identified by the Central Water Commission (CWC) as drought-prone in the country. Most of the drought-prone areas so identified are concentrated in the states of Rajasthan, Karnataka, Andhra Pradesh, Maharashtra and Gujarat.

Human factors that influence drought include incurred demand of water through population growth and agricultural practices; modification of land use that directly influences storage conditions; and hydrological response of catchments and their vulnerability to drought. As pressures on water resources grow, so does vulnerability to meteorological/hydrological/ agricultural drought.

ADVERTISEMENTS:

It may be noted that during the last 50 years, there was no occasion when the percentage area of the country affected by drought was more than 50. In 124 years, probability of occurrence of drought was found maximum in west Rajasthan (25 per cent), Saurashtra and Kutch (23 per cent), followed by Jammu and Kashmir (21 per cent), and Gujarat (21 per cent)