Various parts of the country are reeling under a severe drought. Various ministries of the Government of India have initiated relief measures in drought prone areas. But when is a drought declared in any part of the country? What are the different parameters that are taken into account?

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There is no universally accepted standard definition of drought because of its varying characteristics and impacts across different regions. According to the ‘Drought Management Manual’ released by the Ministry of Agriculture, drought is a recurrent feature of climate and occurs in all climatic regimes. Conditions of drought appear when the rainfall is deficient in comparison to the statistical multi-year average for a region, over an extended period of a season or year, or even more.

Unlike other natural disasters, drought is different in the sense that

• It is difficult to determine the beginning and end of the event
• Duration may range from months to years
• No single indicator or index can identify precisely the onset and severity and its potential impacts
• Multiple indicators are usually more effective
• Spatial extent is usually much greater than that for other natural hazards
• Impacts are generally non-structural and difficult to quantify
• Impacts are cumulative and the effects magnify when events continue from one season to the next

There are many adverse direct and indirect impacts of drought. The impacts could be broadly categorized into Economic, Environmental & Social.

Economic: Economic impacts of drought include production losses in agriculture and other related sectors. It causes loss of income resulting in reduction of purchasing power especially among those dependent on agriculture and living in the rural areas. It also has a multiplier effect on other sectors dependent on agriculture for raw material.

Environmental: Decreased water levels in reservoirs, canals, ponds are the primary environmental impacts. This will lead to decreased availability of drinking water and water for other needs. It will also cause loss of forest cover etc.

Social: Migration of population is the top most social impact resulting out of lack of income. Decrease of income also leads to people withdrawing children from schools, postponement of marriages, sale of assets etc. It will also lead to inadequate food leading to malnutrition and other health hazards.

The four indicators viz., rainfall deficiency, the extent of area sown, normalized difference vegetation index and moisture adequacy index are usually applied in combination for drought declaration. The information on these indicators is available at the level of Taluka / Tehsil / Block. Drought may be declared by the State Government at these levels.

Rainfall Deficiency: Rainfall is the most important indicator of drought. A departure in rainfall from its long-term averages is taken as the basis for drought declaration. The departure could be either measured for specific months or an entire season. Rainfall data are easily available and simple to apply. The rainfall data can be applied in two ways

• The State Government could consider declaring a drought if the total rainfall received during the months of June and July is less than 50% of the average rainfall for these two months and there is an adverse impact on vegetation and soil moisture
• The State Government could consider declaring a drought if the total rainfall for the entire duration of the rainy season of the state, from June to September (the south-west monsoon) and/or from December to March (north-east monsoon), is less than 75% of the average rainfall for the season and there is an adverse impact on vegetation and soil moisture

Area under Sowing: Sowing is another important indicator of the spread and severity of drought. Drought conditions could be said to exist if along with the other indicators, the total area sown by the end of July/August is less than 50% of the total cultivable area. In case of Rabi crops, the declaration of drought could be linked to the area of sowing being less than 50% of the total cultivable area by the end of November/December along with the other indicators.

Normalized Difference Vegetation Index (NDVI): The National Agricultural Drought Assessment and Monitoring System (NADAMS), instituted by the National Remote Sensing Centre (NRSC), issues a bi-weekly drought bulletin and monthly reports on detailed crop and seasonal condition during the kharif season. These present the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Wetness Index (NDWI). These reports provide quantitative information on sowings, surface water spread and District / Tehsil / Taluk /Block level crop condition assessment along with spatial variation in terms of maps. At present, 12 agriculturally important and drought-vulnerable States of Andhra Pradesh, Bihar, Gujarat, Haryana, Karnataka, Maharashtra, Madhya Pradesh, Orissa, Rajasthan, Tamil Nadu, Telangana and Uttar Pradesh are covered through these reports.

Moisture Adequacy Index (MAI): Moisture Adequacy Index (MAI) is based on a calculation of weekly water balance, is equal to the ratio (expressed as a percentage) of Actual Evapo Transpiration (AET) to the Potential Evapo Transpiration (PET) following a soil–water balancing approach during a cropping season.

Certain other factors are also taken into consideration before declaration of drought.

Since independence, there have been 15 drought years, from 1951 to 2002, in 1951, 1952, 1965, 1966, 1968, 1969, 1971, 1972, 1974, 1979, 1982, 1985, 1986, 1987 and 2002. The frequency of droughts has varied with 2 drought years in the 1950s and four in the 1960s. The 1970s and 1980s also had four drought years each. The 1990s did not see a single drought year. The next drought again was in 2002.

The 1987 drought was the worst drought after independence affecting 59–60% of the crop area and a population of 285 million. In 2002 too, over 300 million people spread over 18 States were affected by drought in varying degrees. Around 150 million cattle were affected due to lack of fodder and water. Food grains production registered the steepest fall of 29 million tonnes. No other drought in the past had caused reduction in food grain production to this extent.

Various ministries of the Government of India viz., Agriculture, Rural Development, Drinking Water, Animal Husbandry, Food & Public Distribution, Water Resources, Home Affairs, Finance and Railways are involved in planning and implementing the relief measures.The state governments submit reports on drought condition with all the relevant information and the government of India extends support based on these reports. The various relief measures include financial assistance to states, contingency crop planning, relief employment, food security and initiatives to mitigate the impacts.