As an example, the Palmer Drought Severity Index (PDSI) (Figure 11.5) and Crop Moisture
Index (CMI) are indices of the relative dryness or wetness affecting water-sensitive economies. The
Palmer Index uses temperature and rainfall information in a formula to determine dryness. It has
become the semiofficial drought index. The Palmer Index is most effective in determining longterm
drought—a matter of several months—and is not as good with short-term forecasts (a matter
of weeks). It uses a 0 as normal, and drought is shown in terms of minus numbers; for example, −2
is moderate drought, −3 is severe drought, and −4 is extreme drought. Tools used in the Drought
Outlook (Figure 11.6) include the official CPC long-lead precipitation outlook for November–January
2007/08, the four-month drought termination and amelioration probabilities, various medium- and
short-range forecasts, and models such as the 6–10-day and 8–14-day forecasts, the soil-moisture
tools based on the Global Forecast System model and the Constructed Analogue on Soil Moisture,
and the Climate Forecast System (CFS) monthly precipitation forecasts.