Drought Trends

Drought is an extend period of below-average precipitation that leads to some kind of impacts (crops, water supplies, etc.). It is a familiar feature of the climate of Illinois.

Droughts were very common in the first part of the 20th century and much rarer since 1965. Illinois experienced statewide extreme drought 8 times between 1895 and 1965. The well-known droughts of the 1930s and 1950s stand out as well as lesser known droughts in 1902, 1915, 1940, and 1964. Since 1965, extreme drought has occurred only twice (1988-89, and 2012). While both of the more recent droughts were costly, they were shorter-lived and less intense than many of the droughts from the earlier 20th century.

The figure below shows the state-wide monthly Palmer Drought Severity Index (PDSI) for Illinois since 1895. The PDSI is one measure of drought, combining the effects of both temperature and precipitation. More information on the PDSI can be found below. A value of less than -4.0 indicates an “extreme drought.”

Figure 1: Illinois Drought Trend. Palmer Drought Severity data provided by NOAA.

Description and Data
Palmer Drought Severity Index (PDSI) is the monthly value (index) that is generated indicating the severity of a wet or dry spell. This index is based on the principles of a balance between moisture supply and demand. Man-made changes were not considered in this calculation. The index generally ranges from -6 to +6, with negative values denoting dry spells and positive values indicating wet spells. There are a few values in the magnitude of +7 or -7.

PDSI values 0 to -.5 = normal; -0.5 to -1.0 = incipient drought; -1.0 to -2.0 = mild drought; -2.0 to -3.0 = moderate drought; -3.0 to -4.0 = severe drought; and greater than – 4.0 = extreme drought. Similar adjectives are attached to positive values of wet spells. This is a climatological drought index used to assess the severity of dry or wet periods.

Year    Jan    Feb    Mar    Apr    May    Jun    Jul    Aug    Sep    Oct    Nov    Dec
1895   0.04  -0.55  -1.10  -1.65  -2.16  -2.62  -1.68  -1.82  -1.93  -2.41   0.08   0.98   
1896  -0.27  -0.17  -0.53  -1.14   0.37   0.43   1.60   1.38   2.39   2.08   2.39   1.59   
1897   2.62   2.48   3.52   3.53  -0.56  -0.23  -0.28  -1.14  -2.27  -3.37  -3.07  -3.01   
1898   0.98   1.03   2.79   2.48   2.92   2.67   2.17   2.28   2.53   3.00   3.02   2.55   
1899   2.35   2.31   2.23  -0.91  -0.22  -0.73  -0.71  -1.15  -1.55  -1.48  -2.03  -2.19   
1900  -2.37  -0.99  -1.21  -2.00  -1.90  -1.43  -0.94  -0.69  -0.56  -0.80  -0.66  -1.09   
1901  -1.12  -1.06  -0.73  -1.33  -1.88  -2.06  -2.86  -3.49  -3.90  -4.07  -4.76  -4.78   
1902  -5.02  -5.18  -4.83  -4.72  -4.46   1.82   2.08   2.59   3.02   2.75   2.90   3.08   
1903   2.60   2.89   2.36   2.38   1.69   1.39   1.28   1.65   1.70   1.53   0.92   0.57   
1904   1.03   0.83   2.20   2.26   1.84   1.45   1.88   2.23   2.83  -0.46  -1.17  -1.32   
1905  -1.25  -1.18  -1.59   0.02   0.15  -0.21   0.69   0.72   0.57   1.21   1.19   1.08   
1906   1.63   1.67   2.08  -0.75  -1.22  -1.31  -1.63   0.06   0.49   0.08   0.41   0.78   
1907   2.40   1.56   1.15   1.05   1.23   1.52   2.27   3.19   2.88   2.54   2.55   2.53   
1908   2.13   3.24   2.77   2.83   3.90  -0.37  -0.41  -0.87  -1.82  -2.68  -3.03  -3.69   
1909  -3.51   0.96   0.58   1.62   1.60   1.54   2.01   1.25   1.40   1.38   1.61   1.87   
1910   1.80   1.71  -1.68  -1.96   0.62  -0.54  -0.34  -0.60   0.48   0.62  -0.38  -0.72   
1911  -0.62  -0.32  -0.89  -0.14  -1.17  -1.82  -2.44   0.09   2.04   2.18   2.67   2.50   
1912   1.96   1.80   1.93   2.22   1.82   1.55   1.70   1.90   1.55   1.61   1.25   0.62   
1913   1.66   1.38   2.41  -0.31  -0.71  -1.33  -2.07  -2.74  -2.82  -2.53  -2.64  -3.23   
1914  -3.13  -2.54  -2.60  -2.91  -3.35  -3.80  -4.63  -4.55  -4.11  -3.87  -4.78  -4.96   
1915  -4.55  -4.08  -4.48  -5.22   1.02   1.44   2.76   4.11   4.27   3.40   3.13   3.19   
1916   5.00  -0.39  -0.75  -1.40  -1.05  -0.09  -1.26  -1.09  -1.17  -1.10  -1.57  -1.68   
1917  -1.50  -1.94  -1.89   0.53   0.84   1.54  -0.22  -0.36  -0.50  -0.08  -0.77  -1.41   
1918  -1.18  -1.14  -2.20   0.86   0.97   0.70   0.23   0.09   0.50   0.54   0.34   0.68   
1919  -0.58  -0.42  -0.31  -0.80   0.59   0.66  -0.77  -1.01  -1.03   1.33   1.80  -0.48   
1920  -0.57  -1.04   0.78   1.24   1.53  -0.68  -1.09  -1.25  -1.59  -2.06  -2.93  -3.10   
1921  -3.25  -3.64  -2.88  -2.28  -2.87  -2.97  -3.82   0.49   1.37   1.12   1.32   1.56   
1922   1.17   0.89   2.10   2.37  -0.34  -1.37  -1.34  -2.12  -2.78  -3.06  -3.43  -3.55   
1923  -3.54  -3.47  -2.47  -2.66  -2.19  -2.18  -2.61   0.51   0.71   1.16   0.83   1.19   
1924  -0.02  -0.09  -0.14  -0.78   0.10   1.35   1.31   2.08   2.19  -0.60  -1.05  -0.54   
1925  -0.98  -0.86  -1.21  -1.79  -2.40  -1.97  -2.05  -2.26   0.24   0.93   1.20  -0.21   
1926  -0.26   0.34  -0.08  -0.01  -0.75   0.24   0.14   0.62   3.06   3.53   4.14   3.53   
1927   3.44   2.85   3.08   4.01   4.77   4.48   4.01   3.80   4.03   4.08   4.70   4.64   
1928   3.85   3.67   2.60   2.37   1.59   2.94   2.57   2.34   1.88   2.14   2.40   2.32   
1929   2.99   2.42   2.07   2.34   2.93   3.11   3.27   2.76   2.42   2.55   2.25   2.18   
1930   3.19  -0.02  -0.67  -1.13  -1.88  -1.98  -3.11  -3.80  -3.67  -3.72  -4.20  -5.03   
1931  -5.64  -6.21  -6.48  -6.34  -5.46  -5.39  -5.28   0.12   0.39   0.51   0.96   1.18   
1932   1.53  -0.29  -0.42  -1.14  -1.73  -1.69  -1.82   0.84   0.73   1.13   0.90   1.56   
1933   1.68   1.35   1.63   1.45   2.71  -1.28  -2.03  -2.40  -2.55  -2.47  -3.46  -4.15   
1934  -4.53  -5.12  -5.45  -5.69  -6.48  -6.75  -6.90  -6.39   1.16   0.53   1.27   1.07   
1935   1.23   0.97   1.21   0.79   2.33   2.98  -0.14  -0.55  -0.52  -0.81  -0.19  -0.48   
1936  -0.59  -0.46  -1.18  -1.38  -2.23  -3.06  -4.45  -5.14   0.87   0.87   0.50   0.51   
1937   2.20   1.85   0.97   1.39   0.92   1.28  -0.11  -0.61  -0.94  -0.50  -0.86  -0.97   
1938   0.30   0.49   1.19   0.79   1.07   1.52   1.91   0.04  -0.07  -0.76  -1.05  -1.36   
1939   0.51   1.21   1.10   1.65  -0.78   0.40   0.29   0.82  -1.20  -1.52  -2.27  -3.03   
1940  -3.30  -3.41  -3.55  -2.95  -2.71  -2.82  -3.45  -2.96  -3.82  -4.06  -4.13  -4.29   
1941  -3.81  -3.86  -4.11  -3.82  -3.94  -3.38  -3.40  -3.55   0.47   2.78   2.91   2.45   
1942   2.02   2.55   2.15   1.29   1.25   1.75   2.08   2.07   1.97   1.56   2.27   2.37   
1943   1.90   1.38   1.22   1.17   2.82  -0.21  -0.55  -0.92  -1.11  -1.37  -1.84  -2.46   
1944  -3.05   0.01   0.59   1.74  -0.15  -0.90  -1.64  -1.53  -1.68  -2.32  -3.00  -3.57   
1945  -3.95  -3.65   1.08   1.55   2.12   3.18   2.15   1.89   3.33   2.93   2.97   2.72   
1946   2.59   2.48   1.59   0.59   1.47   1.49   0.80   1.76   1.20   1.08   1.55   1.49   
1947   1.52  -0.75  -0.82   1.09   1.28   2.24  -0.54  -1.31  -1.23  -1.42  -1.66  -1.87   
1948  -1.87   0.20   1.05  -0.84  -0.78  -0.74   0.77  -0.59  -0.80  -1.00  -0.04   0.08   
1949   1.90   2.12   1.97  -0.70  -1.25  -1.22  -1.01  -1.18  -1.13   0.67  -0.71   0.78   
1950   2.87   3.60   3.03   3.55   2.54   2.94   3.00   3.02   2.91   1.99   1.92   1.49   
1951   1.53   2.47   2.52   2.31   1.68   2.42   2.71   2.79   2.83   2.83   3.31   3.21   
1952   2.84   2.47   2.85  -0.04  -0.21  -0.20  -0.36  -0.49  -1.03  -1.67  -1.89  -2.12   
1953  -2.06  -1.98  -1.17  -1.20  -1.51  -1.85  -1.77  -2.74  -3.39  -3.92  -4.96  -5.55   
1954  -5.72  -5.97  -6.09  -5.50  -5.23  -5.09  -5.13  -4.11  -4.43  -3.24  -3.44  -3.09   
1955  -2.75  -2.05  -2.07  -2.06  -1.96  -1.64  -1.78  -2.15  -2.29  -1.50  -1.58  -2.17   
1956  -2.50  -1.67  -2.31  -2.04  -1.91  -2.36  -1.68  -1.24  -1.93  -2.84  -3.14  -3.24   
1957  -2.96  -2.51  -2.62   1.30   1.90   2.66   2.67   2.25   1.44   1.63   1.88   2.57   
1958  -0.07  -0.58  -1.04  -1.29  -1.66   0.99   2.84   2.67  -0.05  -0.47  -0.14  -0.66   
1959   0.31   0.64  -0.01  -0.22  -0.28  -1.29  -1.40   0.03   0.12   0.64   0.55   0.67   
1960   0.83   1.00  -0.18  -0.38   0.31   0.98  -0.12  -0.32  -1.02  -1.09  -1.46  -1.85   
1961  -2.36  -2.19   0.51   0.55   1.09   0.75   1.62   1.51   2.90   2.87   3.36   3.21   
1962   3.53   3.47   3.21  -0.66  -0.79  -0.97  -0.27  -0.55  -0.70  -0.57  -1.13  -1.71   
1963  -2.19  -2.66  -1.60  -1.92  -2.07  -2.70  -1.94  -1.91  -2.52  -3.48  -3.92  -4.63   
1964  -4.84  -5.05  -4.00  -2.93  -3.68  -3.66  -3.66  -3.87  -3.85  -4.55  -4.73  -4.98   
1965   0.58   0.64   0.59   0.97   0.15   0.08   0.08   1.26   2.62  -0.18  -0.48  -0.12   
1966  -0.29  -0.03  -0.77   0.83   1.14  -0.54  -1.31  -1.56  -1.26  -1.50  -1.49   0.40   
1967   0.41  -0.20  -0.47   0.17   0.32   0.29   0.88   0.78   0.76   1.69   1.90   2.88   
1968  -0.09  -0.33  -0.86  -1.02  -0.42  -0.28  -0.22  -0.38  -0.13  -0.76   0.40   0.74   
1969   1.55  -0.31  -0.63  -0.33  -0.71   0.82   1.86   1.26   1.48   2.74   2.50   2.23   
1970   1.50   0.97   0.75   1.57   1.71   2.29   1.96   1.94   3.41   3.61   3.29   2.76   
1971   2.29   2.65  -0.58  -1.51  -1.53  -2.01  -1.15  -1.60  -1.59  -2.20  -2.82   0.71   
1972  -0.32  -0.54  -0.52   0.79   0.06   0.07   0.22   1.08   1.73   1.85   2.79   3.13   
1973   2.80   2.22   3.19   3.73   3.80   4.19   4.22   3.33   3.19   3.17   3.12   3.69   
1974   4.01   3.88   3.55   3.16   4.01   4.46   3.22   3.29   2.95   2.28   2.08   1.80   
1975   2.35   2.75   2.75   2.87   2.49   2.20   1.94   2.39   2.20  -0.36  -0.40  -0.24   
1976  -0.55   0.09   0.53  -0.50  -0.42  -0.74  -0.80  -1.29  -1.55  -1.12  -1.76  -2.59   
1977  -2.94  -3.11  -1.93  -2.66  -3.13  -2.95  -2.85   1.47   2.08   2.75   2.87   2.86   
1978  -0.24  -0.73   0.19   0.12   0.49   0.07   0.46  -0.02  -0.33  -0.58   0.02   0.37   
1979   0.78   0.72   1.31   2.18   1.36   0.75   1.44   1.98  -0.99  -1.28  -1.19  -1.26   
1980  -1.51  -1.58  -1.10  -1.38  -1.74  -1.38  -1.63   0.55   0.98  -0.02  -0.52  -0.78   
1981  -1.34  -0.93  -1.70   0.28   1.21   1.61   2.65   3.71   3.47   3.40   3.17   2.79   
1982   3.56   2.98   3.00   2.71   2.33   2.22   2.97   2.95   2.67   2.53   3.08   4.74   
1983   3.76   3.08   2.80   3.73   4.05   3.60   2.41   1.31   0.68   1.12   1.81   2.26   
1984   1.59   1.60   2.07   2.45   2.69  -0.76  -0.89  -1.69   0.39   0.97   1.51   2.05   
1985   1.76   2.45   2.98   1.87   1.24   1.42   1.27   2.10   1.41   1.74   4.15   3.90   
1986  -0.67  -0.09  -0.89  -1.72  -1.54  -1.50   0.72   0.36   1.43   2.33   2.29  -0.09   
1987  -0.18  -0.68  -1.20  -1.60  -2.29  -2.57   0.02   0.77  -0.51  -0.86  -0.86   0.94   
1988   0.97   0.98   0.95  -0.73  -1.60  -2.78  -3.32  -3.91  -4.17  -3.89   0.39   0.28   
1989   0.13   0.30  -0.03  -0.18  -0.25  -0.51  -0.51   0.23   0.96  -0.32  -0.72  -1.28   
1990  -0.04   1.11   0.97   0.60   2.08   2.75   2.82   2.83   2.06   2.55   2.99   4.08   
1991  -0.06  -0.43  -0.12  -0.42  -0.40  -1.43  -2.17  -2.55  -2.56   0.97   1.38   1.30   
1992  -0.26  -0.46  -0.75  -0.91  -1.78  -2.44   1.39   0.90   1.42   0.91   2.26   2.37   
1993   2.90   2.70   2.57   2.99   2.37   3.29   4.10   4.49   6.11   5.86   6.31  -0.13   
1994  -0.05  -0.02  -0.81   0.86  -0.63  -0.63  -0.91  -0.73  -1.01  -1.31   0.59   0.45   
1995   0.99   0.55   0.11   0.49   2.21  -0.16  -0.39  -0.39  -1.04  -0.93  -1.01  -1.38   
1996  -1.06  -1.39  -1.50   0.65   1.92   1.80   2.15   1.46   1.29   1.05   1.18   0.95   
1997   1.15   2.06  -0.10  -0.44  -0.19  -0.27  -0.77  -0.05  -0.39  -0.70  -0.90  -1.13   
1998   0.35   0.55   1.15   1.48   1.32   2.62   2.33   2.04   1.30   1.68   1.40   1.03   
1999   1.96   1.94   1.23   1.72   1.30   1.61  -0.42  -0.63  -0.95  -1.31  -2.55  -2.74   
2000  -2.83  -2.38  -2.78  -2.72  -0.04   1.29   1.67   1.65   1.83   1.47   1.69   1.54   
2001   1.35   1.96  -0.70  -1.22   0.05   0.05   0.15   0.42   0.59   1.93   1.92   1.97   
2002   1.96   1.79   1.83   2.10   3.22  -0.13  -0.64  -0.32  -0.95  -0.74  -1.43  -1.64   
2003  -2.09  -1.85  -2.17  -2.16   0.61   0.66   1.20   0.83   1.31   1.06   1.64   1.73   
2004   1.63  -0.47  -0.08  -0.91   0.79   0.46   0.71   1.67   0.63   1.40   2.26   2.01   
2005   3.35   0.04  -0.57  -1.12  -1.78  -2.63  -2.80  -2.72  -2.67  -3.20  -3.23  -3.74   
2006  -3.34  -3.39   0.64  -0.22  -0.37  -0.68   0.09   0.31   0.51   1.07   1.38   1.84   
2007   2.18   2.26  -0.19  -0.14  -1.00  -0.98  -0.94  -0.73  -1.52  -1.38  -1.90   0.30
2008   0.53   1.78   2.25   2.32   2.72   3.04   3.71   3.04   4.59   4.36   3.93   4.52
2009   3.73   3.73   3.72   4.27   4.37   4.34   4.58   4.99   4.41   6.56   6.10   6.32
2010   5.56   4.92   4.20   3.31   3.40   4.29   4.52   3.99   3.81   2.91   2.60   2.15
2011   1.67   2.20   1.77   2.98   3.07   3.64  -0.07  -0.70  -0.48  -0.84   0.52   0.94
2012   0.89  -0.17  -1.29  -1.51  -2.24  -3.06  -4.35  -4.28  -3.37  -2.62  -3.07  -3.14
2013   0.72   1.12   1.00   2.27   2.86   3.10  -0.02  -0.73  -1.44  -1.20  -1.31  -1.25
2014  -1.12  -0.74  -1.18   0.56   0.15   1.14   1.17   1.96   2.36   3.04   3.04   2.77
2015   2.38   2.01   1.56   1.14