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Palmer Drought Severity Index (long term)
The PDSI is updated weekly by the 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, and does not reflect snowpack, an important component of water supply in the western United States.
Crop Moisture Index (short term)
The Crop Moisture Index, updated weekly by the Climate Prediction Center, is a derivative of the Palmer Drought Index, designed to reflect quickly changing soil moisture conditions.
Standardized Precipitation Index
The SPI is a relatively new drought index, based only on precipitation. The SPI can be calculated for a variety of time scales. This flexibility allows the SPI to be useful in both short-term agricultural and long-term hydrological applications.
U.S. Drought Assessment
On Thursdays, the CPC together with the U.S. Department of Agriculture, and the National Drought Mitigation Center in Lincoln, Nebraska, issues a weekly drought assessment called the U.S. Drought Monitor. These assessments review national drought conditions and indicate potential impacts for various economic sectors, such as agriculture and forestry.
NDMC Drought Monitor Page
The Drought Monitor was introduced as an operational weekly product in 1999 to provide an overview of conditions averaged across a broad array of time scales and impact indicators, leaning toward those that seem most relevant to observed impacts.
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