Crop Moisture Index (CMI)
Index name: Crop Moisture Index (CMI).
Ease of use: Yellow.
Origins: As part of original work done by Palmer in the early 1960s, CMI is usually calculated weekly along with the Palmer Drought Severity Index (PDSI) output as the short-term drought component in which the impact on agriculture is considered.
Characteristics: As some of the drawbacks associated with PDSI became apparent, Palmer responded to them with the development of CMI. It is intended to be a drought index especially suited to drought impacts on agriculture, in that it responds quickly to rapidly changing conditions. It is calculated by subtracting the difference between potential evapotranspiration and moisture, to determine any deficit.
Input parameters: Weekly precipitation, weekly mean temperature, and the previous week’s CMI value.
Applications: Used to monitor droughts in which agricultural impacts are a primary concern.
Strengths: The output is weighted, so it is possible to compare different climate regimes. Responds quickly to rapidly changing conditions.
Weaknesses: As it was developed specifically for the grain-producing regions in the United States, CMI may show a false sense of recovery from long-term drought events, as improvements in the short term may be insufficient to offset long-term issues.
Reference: Palmer, W.C., 1968: Keeping track of crop moisture conditions, nationwide: the Crop Moisture Index. Weatherwise, 21: 156–161.