Drought Monitoring Techniques for Famine Early Warning Systems in Africa - Monitoring and Predicting Agricultural Drought: A Global Study - page 254

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having mandates and resources for response to food security emergencies.
Targeting their responses directly benefits from FEWS NET analyses that
identify the location and intensity of needs.
Early detection and early warning of famine must be persuasive enough
to overcome the risk avoidance behaviors of decision-makers in respon-
sible organizations—national governments, donor agencies, international
organizations, and NGOs (Cutler, 1993). It is for this reason that FEWS
NET food security analysts rely on a convergence of evidence to make food
security assessments. No single source of information is sufficiently author-
itative and comprehensive to identify potential famine areas alone (Mason
et al., 1987; Shoham, 1987; Kelly, 1993). Therefore, analysts draw their
conclusions most confidently when all factors indicate a certain food secu-
rity status in a region. Any reduction of ambiguity associated with data or
information used by FEWS NET contributes to confidence in food secu-
rity assessments and an improved linkage between early warning and early
response.
In subsequent sections of this chapter we explore traditional and current
methods of monitoring drought and famine used by the FEWS network of
scientists in the United States and Africa. We first discuss traditional use
of satellite-derived vegetation index and rainfall estimates, followed by a
discussion of more complex crop condition modeling using satellite-derived
rainfall and vegetation information.

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R emote Sensing Data for FEWS NET

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In Africa, in general, sparse data observation networks resulting in inade-
quate spatial coverage, data quality, and timely accessibility are problems
that food security analysts often face. The use of remotely sensed data of-
fers solutions to at least part of the problem. Geographically referenced
(geospatial) climate monitoring products offer food security analysts suc-
cinct and practical summaries of crop growing conditions. The products
are accessible in near-real time at a continental scale and are typically the
most comprehensive and up-to-date observational data available, allowing
analyses to be conducted at any administrative level.
Current operational climate monitoring for FEWS NET is based pri-
marily on maximum value composite images of the normalized difference
vegetation index (NDVI; Holben, 1986; Tucker and Sellers, 1986; chapter
5) and rainfall estimate (RFE) images (Herman et al., 1997; Xie and Arkin,
1997) produced on a 10-day time step. The FEWS NDVI archive dates
back to July 1981; the RFE images have only been produced since 1995.
Conventional rain gauge data are also analyzed, though the availability of
these data (http://edcintl.cr.usgs.gov/adds/) varies from country to country,
and there is a significant delay in obtaining data for many stations. These
products are the basis for analyzing climate in the past, present, and fu-
ture. The variability in the historical NDVI and rainfall data is the basis