Agricultural Drought Indices - US Department of Agriculture

(a) IGAD member countries
(b) ICPAC member countries
Figure 1. Map showing the ten Greater Horn of Africa countries served by ICPAC.
Monitoring and detection of agricultural droughts in the sub-region is difficult because it requires
climate information such as evapotranspiration and soil moisture, which is not readily available.
Ideally, this information should be integrated to produce unique indices. ICPAC uses the
Standardized Precipitation Index (SPI) approach to monitor effects of agricultural droughts in the
sub-region. Figure 2, for instance, shows the impacts of drought on agricultural production, which
often result in total crop failure. The objective of this chapter is to present an overview of the
agricultural drought indices in current use in the GHA sub-region, as well as to discuss some of
their strengths and limitations.
Figure 2. Impacts of drought on agricultural production, leading to total crop failure due to
prolonged drought.
Agricultural Drought Assessment and Monitoring over the GHA region
Several indices measure how precipitation for a given period of time has deviated from historically
established norms. Although none of the major indices is inherently superior to the rest in all
circumstances, some indices are better suited than others for certain uses. There are different
types of droughts for any given locality. Meteorological drought is defined as a deficiency of
precipitation from expected or “normal” over an extended period of time. Hydrological drought
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