Monitoring Drought Using Coarse-Resolution Polar-Orbiting Satellite Data - Monitoring and Predicting Agricultural Drought: A Global Study - page 73

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[73],

Line
——
-0.9
——
Norm
PgEn

[73],

Figure 5.11 (a) The NDVI monthly values (bars) and long-term (1982-2000) means (thick
lin e) for Zimbabwe during 1991-93. (b) The annual variation in maize production for Zim-
ba bwe during 1981-2000.

NDVI-like formulations, one can retrieve variations induced by leaf wa-
ter contents. Gao (1996) proposed a normalized difference water index
(NDWI) for detecting and monitoring vegetation liquid water content us-
ing narrow-band ( < 10 nm) data. With the launch of new satellite sensor
systems, more research can be expected on the development of operational
and global drought monitoring approaches involving vegetation water sta-
tus using the SWIR region.
Combining land-surface temperatures (T s ) with vegetation indices (VI)
is also of great interest in drought monitoring studies (Nemani and Run-
ning, 1989). Under drought conditions, soil moisture is reduced, and hence
evapotranspiration declines, causing leaf temperature to rise. Therefore,
thermal infrared energy emitted from the vegetation canopy can be used
to detect increased temperature of leaves to monitor drought conditions.
Vegetation and crop stress indices, such as the surface moisture index (SMI;