The Palmer Drought Severity Index (PDSI) and Crop Moisture Index (CMI) are indices of the relative dryness or wetness effecting water sensitive economies. The PDSI indicates the prolonged and abnormal moisture deficiency or excess.
The CMI gives the short-term or current status of purely agricultural drought or moisture surplus and can change rapidly from week to week.
Both indicies indicate general conditions and not local variations caused by isolated rain. Calculation of the PDSI and CMI are made for 350 climatic
divisions in the United States and Puerto Rico. Input to the calculations include the weekly precipitation total and average temperature, division
constants (water capacity of the soil, etc.) and previous history of the indices.
The PDSI is an important climatoligical tool for evaluating the scope, severity, and frequency of prolonged periods of abnormally dry or wet weather. It can be used to help delineate disaster areas and indicate the availability of irrigation water supplies, reservior levels, range conditions, amount of stock water, and potential intensity of forest fires. The CMI can be used to measure the status of dryness or wetness affecting warm season crops and field activities.