Drought Severity and Coverage Index
The Drought Severity Classification Index is an experimental method for converting drought levels from the U.S. Drought Monitor map to a single value for an area. DSCI values are part of the U.S. Drought Monitor data tables. If you want to compute it yourself, using cumulative Drought Monitor data, add the values for D0 through D4 to get the Drought Severity Classification Index. Or, to see more math, use categorical (not cumulative) Drought Monitor data, and 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 to get the Accumulated DSCI (ADSCI).
Example for five weeks
239 + 238 + 293 + 295 + 293 = 1358