Jefferson County - East-West Gateway Coordinating Council

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Jefferson County – Section 2
TABLE J45 PALMER DROUGHT SEVERITY INDEX MONTHLY
AVERAGE FOR PERIOD OF RECORD
1895 TO 1995
June -1.17 0.57
July 1.24 1.64
August 1.68 1.65
September 1.48 -0.40
October 0.65 -0.93
November 0.81 0.30
December 2.37 1.79
Quantifying a drought is very difficult. The Palmer Index is the most widely known product.
The United States government adopted the Palmer Index as its drought indicator back in
the 1960's and continues to do so today, despite some of its weaknesses.
Within the past few years, the National Drought Mitigation Center has created a U.S.
drought map that utilizes numerous indicators to determine the severity of a drought.
These indicators include the Palmer Index, Crop Moisture Index, Standardized Precipitation
Index, Percent of Normal Rainflow, Daily Streamflow, Snowpack, Soil Moisture, Vegetative
Index, and Fire Danger Classifications. There is also a lot of subjectivity that goes into the
map. The drought authors take heavily into consideration the input they receive from local
experts in terms of the impacts that are being felt.
Frequency of Occurrence
The National Drought Mitigation Center has developed a graphic historic representation of
the frequency of occurrence of areas within the upper Mississippi River Basin experiencing
severe to extreme drought from 1895 to 1995. The graph below depicts the percentage of
areas of the upper Mississippi River Basin that were impacted by drought, including climatic
zones 2 and 5. Based on the NCDC 1980 report, heat and drought events result in the
highest damage (in the range of 120 billion dollars from 1980 to 1999 based on 46
weather related events) when compared to other natural weather hazards. See Figure J47
below.
FIGURE J47 SEASONAL DROUGHT