THE FLOATING MONTH DROUGHT INDEX – A NEW DROUGHT MONITORING TOOL

摘要

Dozens of drought indices have been developedover the 20th century which measure specific aspects ofdrought (from water supply and water demand toimpacts) or have specific applications. In some cases,these indicators may yield inconsistent or conflictingresults. A new drought index (the Floating MonthDrought Index, or FMDI) was developed to addressthese inconsistencies. The FMDI initiates a droughtbased on unusually dry conditions (≤ 30th percentile)over 3 consecutive months. The dry spell ends whenthe total precipitation for the spell period no longer fallsbelow the dry threshold, or the precipitation for the past3 months was unusually wet (≥ 70th percentile). TheFMDI computes the precipitation percentile for thecurrent month and current N-month dry spell, the lengthand starting year/month of the current dry spell, and theDx dry spell category based on USDM categories (andsimilar statistics for wet spells). The FMDI thusprovides an objective decision-support tool forintegrating the multiple time scales of drought.