|
Table 3. PDSI Values for the 11 drought
categories.
|
PDSI Value
|
Category
|
PDSI Value
|
Category
|
|
4.0 and above
|
Extreme moist spell
|
-0.50 to -0.99
|
Incipient drought
|
|
3.0 to 3.99
|
Very moist spell
|
-1.0 to -1.99
|
Mild drought
|
|
2.0 to 2.99
|
Unusual moist spell
|
-2.0 to -2.99
|
Moderate drought
|
|
1.0 to 1.99
|
Moist spell
|
-3.0 to -3.99
|
Severe drought
|
|
0.5 to 0.99
|
Incipient moist spell
|
-4.0 and below
|
Extreme drought
|
|
0.49 to -0.49
|
Near normal
|
|
|
(Source: Wilhite 1987).
Table 4. Estimated occurrence of drought since
1970.
|
Mild - Moderate
|
Severe - Extreme
|
|
Begin
|
End
|
Begin
|
End
|
Begin
|
End
|
Begin
|
End
|
|
1706
|
1708
|
1855
|
1856
|
1717
|
1719
|
1874
|
1876
|
|
1721
|
1721
|
1869
|
1872
|
1735
|
1736
|
1889
|
1890
|
|
1741
|
1743
|
1886
|
1887
|
1756
|
1759
|
1898
|
1900
|
|
1772
|
1774
|
1917
|
1921
|
1798
|
1800
|
1910
|
1913
|
|
1782
|
1785
|
1926
|
1926
|
1808
|
1809
|
1929
|
1940
|
|
1789
|
1791
|
1955
|
1956
|
1816
|
1823
|
1958
|
1961
|
|
|
|
|
|
1847
|
1848
|
1976
|
1977
|
|
|
|
|
|
1862
|
1866
|
1980
|
1981
|
|
|
|
|
|
|
|
1988
|
1992
|
|
