Agricultural Drought Indices - US Department of Agriculture

Agricultural Drought Indices: Summary and Recommendations
Mannava V.K. Sivakumar, World Meteorological Organization, Switzerland
Roger Stone, University of Southern Queensland, Australia
Paulo Cesar Sentelhas, University of São Paulo, Brazil
Mark Svoboda, University of Nebraska, USA
Philip Omondi, IGAD Climate Prediction and Analysis Centre, Kenya
Jayanta Sarkar, India Meteorological Department, India
Brian Wardlow, University of Nebraska, USA
Abstract
Comprehensive drought monitoring that can provide early warnings of drought is a critical
component of national drought strategies. Effective drought early warning systems for agriculture
should integrate a number of climatic parameters with other relevant parameters such as soil
moisture. The Inter-Regional Workshop on Indices and Early Warning Systems for Drought, held
at the University of Nebraska–Lincoln in December 2009, stressed the need for undertaking a
comprehensive review of all agricultural drought indices documented at the workshop to help
identify the prime drought indices for early warning systems most suited for use in the agricultural
sector. Hence the WMO/UNISDR Expert Meeting on Agricultural Drought Indices was organized
and held June 2-4, 2010, in Murcia, Spain. The meeting reviewed several drought indices
currently used around the world for agricultural drought and assessed the capability of these
indices to accurately characterize the severity of drought and its impact on agriculture. This
chapter summarizes the agricultural drought indices that were discussed at the meeting in seven
distinct categories: precipitation-based indices; temperature-based indices; precipitation- and
temperature-based indices; indices based on precipitation, temperature, and soil moisture/soil
characteristics; indices based on precipitation, temperature, relative humidity, solar radiation, wind
speed, and soil moisture/soil characteristics; indices based on remote sensing; and indices based
on a composite approach (multiple indicators/indices). A brief review of each of these indices is
presented. The meeting recommended that given the enhanced availability of and access to data,
tools, and guidance materials, countries around the world should move beyond the use of just
rainfall data in the computation of indices for the description of agricultural droughts and their
impacts. This issue becomes very relevant, especially in the context of climate change, water
scarcity, and food security, and hence it is important to use rainfall, temperature, and soils
information.
Introduction
To meet the increasing global demand for cereals to feed the growing populations, the world's
farmers will have to produce 40% more grain in 2020. The challenge is to revive agricultural
growth at the global level and extend it to those left behind. The causes for the current food crisis
are varied, but civil strife and adverse weather predominate. In the developing countries, where
adoption of improved technologies is too slow to counteract the adverse effects of varying
environmental conditions, climate fluctuations, especially droughts, are indeed the main factors
that prevent a regular supply and availability of food, the key to food security.
Drought is an insidious natural hazard that results from a deficiency of precipitation from expected
or “normal” that, when extended over a season or longer period of time, is insufficient to meet the
demands of human activities and the environment. Drought must be considered a relative, rather
than absolute, condition. A critical component of national drought strategies should be a
comprehensive drought monitoring system that can provide early warning of drought’s onset and
end, determine its severity, and deliver that information to a broad group of users in a timely
manner. With this information, the impacts of drought can be reduced or avoided in many cases.
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