Friday, April 18, 2014

U.S Drought Monitor Statistics Explanation

Two types of statistics are calculated weekly for the U.S. Drought Monitor and each is calculated as a percent area. Below is an explanation of each statistics type.

Traditional Statistics

The traditional U.S. Drought Monitor statistic is a percent of the area at or worse than a certain drought category. These statistics are denoted by the inclusion of two drought categories in the label. For example the D0 or worse category is labeled as D0-D4 and shows the percent of the area that is in D0 or worse.

Note that with these statistics it is not possible to have a higher percent area for a higher drought category. For example the value of D1-D4 can be equal to the value of D0-D4 for a give week, but it can never be higher.

Categorical Statistics

The categorical U.S. Drought Monitor statistic is the percent of the area in a certain drought category only. These statistics are denoted by only one drought category in each label. For example, the D0 category is labeled as D0 and shows the percent of the area that is in D0 only.

Note that these statistics will add up to 100 percent for a given week. It is also possible to have a greater percent of the area in a higher drought category. For example the percent of the area in D1 only could be higher than the percent of the area in D0. However, it is not possible for all six values (including None) to have a total greater than 100 percent for a given week.

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