Drought Severity and Coverage Index
The Drought Severity and Coverage Index is an experimental method for converting drought levels from the U.S. Drought Monitor map to a single value for an area, developed by Adnan Akyuz, North Dakota State Climatologist. Using categorical (not cumulative) Drought Monitor data, we compute a weighted sum:
1(D0) + 2(D1) + 3(D2) + 4(D3) + 5(D4) = DSCI
1(33.75) + 2(14.50) + 3(29.26) + 4(21.69) + 5(.39) = 33.75 + 29 + 87.78 + 86.76 + 1.95 = 239
The utility of the DSCI has not yet been widely tested but it provides a convenient way to convert USDM data from categorical to continuous,
and to aggregate from spatially specific to geopolitical boundaries.
Aggregation over time
People also ask about how to aggregate the U.S. Drought Monitor over time. With the caveat that reducing a series of spatial depictions to a single numeric value inevitably leads to quite a bit of information loss, we recommend summing the DSCI over n weeks, and then dividing by 500 (the highest possible value for a single week) times n, and using the resulting proportion.
Example for five weeks
(239 + 238 + 293 + 295 + 293) / 500 x 5 = .5432