Agricultural Drought Indices - US Department of Agriculture

Monitoring Drought Risks in India with Emphasis on
Agricultural Drought
Jayanta Sarkar
India Meteorological Department, Pune-411005, India
Abstract
This paper highlights the drought indices that are currently in use for monitoring meteorological
and agricultural drought risks in India. For meteorological drought monitoring in India, percentage
rainfall departure from normal is used as an index. The Standardized Precipitation Index (SPI),
which is being developed and tested, has also shown promise in monitoring meteorological
drought. Drought risks have been identified by delineating the country into chronically (probability
of drought occurrence exceeds 20%), frequently (probability of drought occurrence 10% -20%),
and least drought prone (probability of drought occurrence less than 10%) areas. No trend in
meteorological drought has been found to exist in India. For monitoring and assessing agricultural
drought, an aridity anomaly index is used in India. Remote sensing applications could also be very
effective in assessing severity of agricultural droughts, their impacts on sectors like agriculture, and
related policy decisions.
Introduction
The economy of India is greatly dependent on water resources as well as rainfall. The erratic
nature of monsoon rainfall gives rise to low rainfall in some years (leading to drought) and normal
to excess rainfall in others. Drought, which may lead to famine, is indeed one of the worst
environmental hazards because its onset is slow, the affected area is quite widespread, and the
adverse impacts are ruinous. Drought imparts a creeping long-term setback to the socio-economic
fabric of the society which has the misfortune to be visited by it (Kulshrestha 1997). During the 30-
year period 1963-1992, although the number of deaths directly attributable to droughts is much
less (3%) compared to that caused by floods (26%) and tropical cyclones (19%), the number of
persons affected by drought (33%) is the highest among all the natural disasters (number of
persons affected by floods and tropical cyclones being 32% and 20%, respectively), and the
damage caused by drought is significant (22%) and is comparable to the corresponding values of
floods (32%) and tropical cyclones (30%) (WMO 1994). India gets nearly 80% of its annual rainfall
during the southwest monsoon season (June to September). Delayed onset of the monsoon,
prolonged breaks in the monsoon during the normally most active months of July and August, early
withdrawal of the monsoon, and erratic distribution of rainfall during monsoon season make our
country, especially the low rainfall belts, vulnerable to droughts.
For proper monitoring and assessment of droughts, different drought indices are used. India
Meteorological Department (IMD) monitors meteorological and agricultural drought based on
“percentage of rainfall departure” and “aridity anomaly index,” respectively, whereas the National
Remote Sensing Center (NRSC), Hyderabad, monitors agricultural drought using remote sensing
techniques. The Standardized Precipitation Index (SPI) has also been found to be an effective tool
in monitoring meteorological drought.
Drought Monitoring in India
A well-established drought monitoring system exists in India. IMD and NRSC have been
monitoring drought over the country by the conventional way of rainfall monitoring and remote
sensing methods, respectively.
IMD monitors both meteorological drought and agricultural droughts. Meteorological drought over
an area is defined as a situation when the monsoon seasonal (June-September) rainfall over the
area is less than 75% of its long-term average value. It is further classified as “moderate drought”
if the rainfall deficit is 26-50% and “severe drought” when the deficit exceeds 50% of the normal.
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