Drought Indices
Palmer Drought Severity Index (PDSI): attempts to measure
the duration and intensity of the long-term drought-inducing circulation patterns.
Long-term drought is cumulative, so the intensity of drought during the current
month is dependent on the current weather patterns plus the cumulative patterns
of previous months. The PDSI is updated weekly by the NOAA Climate Prediction Center.
It is based on rainfall, temperature and historic data, and is computed based on
a complex formula devised by W.C. Palmer in 1965. Although the Palmer is the main
drought index used by the U.S. government, it is slow to detect fast-emerging droughts.
(Details)
Palmer Hydrological Drought Index (PHDI):
measures hydrological impacts of drought (e.g., reservoir levels, groundwater levels,
etc.) which take longer to develop and longer to recover. This long-term drought
index was developed to quantify these hydrological effects, and it responds more
slowly to changing conditions than the PDSI. (Details)
Crop Moisture Index (CMI): The Crop Moisture Index (CMI)
uses a meteorological approach to monitor week-to-week crop conditions. It was developed
by Palmer (1968) from procedures within the calculation of the PDSI. (Details)
Palmer Z Index: measures short-term drought
on a monthly scale.
Sources:
National Climatic Data Center (NCDC) Palmer Drought Indices
National Drought
Mitigation Center (NDMC) Drought Monitor
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