Agricultural Drought Indices - US Department of Agriculture

Agricultural Drought—WMO Perspectives
Mannava V.K. Sivakumar
World Meteorological Organization, Switzerland
Abstract
The increasing frequency and magnitude of droughts in recent decades and the mounting losses
from extended droughts in the agricultural sector emphasize the need for assigning an urgent
priority to addressing the issue of agricultural droughts. As the United Nations specialized agency
with responsibility for meteorology and operational hydrology, WMO, since its inception, has been
addressing the issue of droughts. In this respect, WMO promotes systematic observation,
collection, analysis, and exchange of meteorological, climatological, and hydrological data and
information; drought planning preparedness and management; research into the causes and
effects of climate variations and long-term climate predictions with a view to providing early
warning; capacity building; and the transfer of knowledge and technology.
The fight against drought receives a high priority in the Long-term Plan of WMO, particularly under
the Agricultural Meteorology Programme, Hydrology and Water Resources Programme, and
Technical Cooperation Programme. Within the context of this Plan, WMO continues to encourage
the greater involvement of the national Meteorological and Hydrological Services (NMHSs) and
regional and subregional meteorological and hydrological centers in addressing the issues of
drought.
This paper presents a short description of the perspectives of the World Meteorological
Organization (WMO) on drought in general and agricultural drought in particular. This is followed
by a short narrative on WMO’s activities in the area of drought. The Commission for Agricultural
Meteorology (CAgM) of WMO since 1967 has appointed a number of working groups and
rapporteurs with specific terms of reference. These have mainly addressed several applications,
including drought monitoring, forecasting, and control; meteorological aspects of drought
processes; operational use of agrometeorology; measures to alleviate the effects of droughts;
assessment of the economic impacts; and capacity-building activities. A number of different
indices have been used to describe agricultural droughts, and some examples are presented.
The role played by NMHSs in drought monitoring, risk assessment, and early warning is described
with examples from China, South Africa, and Portugal. WMO has also been placing considerable
importance on organizing capacity-building activities in the area of drought preparedness and
management, especially in the developing countries, and a list of activities carried out since 1990
is presented. WMO’s support in strengthening the capabilities of regional institutions with droughtrelated
programs and in promoting collaboration with other institutions in drought- and
desertification-prone regions is described.
Introduction
Drought is a normal, recurrent climatic feature that occurs in virtually every climatic zone around
the world, causing billions of dollars in loss annually for the farming community. Drought ranks first
among all natural hazards according to Bryant (1991), who ranked natural hazard events based on
various characteristics, such as severity, duration, spatial extent, loss of life, economic loss, social
effect, and long-term impact. This is because, compared to other natural hazards like flood and
hurricanes that develop quickly and last for a short time, drought is a creeping phenomenon that
accumulates over a period of time across a vast area, and the effect lingers for years even after
the end of drought (Tannehill 1947). Hence, the loss of life, economic impact, and effects on
society are spread over a long period of time, which makes drought the worst among all natural
hazards. For example, the Murray-Darling River Basin in Australia was subjected to periods of
protracted drought with two decade-long droughts in the last century. Since 2001 it has been
experiencing the worst drought in recorded history. System inflows in the three years ending
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