U.S. Drought Monitor

Statistics Explanation

Ways of computing Drought Monitor statistics


Statistics are calculated weekly for the U.S. Drought Monitor by two different methods that we refer to as “cumulative,” which is how we did it from the beginning, or “categorical,” meaning we report on one category at a time. Below is an explanation of each method.

  Absolute Values Cumulative Statistics Categorical Statistics
Area, Absolute Sq miles in drought Reports areas from D0 through D0-4 Reports areas one drought category at a time
Area, Proportional % of area Reports areas from D0 through D0-4 Reports areas one drought category at a time
Population, Absolute People in drought Reports population from D0 through D0-4 Reports population one drought category at a time
Population, Proportional % of people (in area) Reports population from D0 through D0-4 Reports population one drought category at a time

Regular calculations


Up to four types of statistics are calculated for the drought monitor depending on the area in question.

  • PERCENT AREA STATISTICS provide the percent of the chosen area in each USDM category.
  • TOTAL AREA STATISTICS show the square miles of an area in each USDM category.
  • PERCENT POPULATION STATISTICS provide the proportion of the population affected in each USDM category.
  • TOTAL POPULATION STATISTICS provide the number of people affected in each USDM category.

Get more information about how the population in drought numbers are calculated.