. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. DROUGHT IMPACTS ON WATER RESOURCES 582 > 581. > 577 575 1961 1966 1971 1976 1981 1986 Figure 1. Lake Michigan water level, 1961-1992 1991 indicates that the 1893-1895 drought may have had as extensive an impact as the 1952-1955 drought in many parts of Illinois. However, there are no streamflow records for this earlier drought. The major difference between a moderate and severe streamflow drou
. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. DROUGHT IMPACTS ON WATER RESOURCES 582 > 581. > 577 575 1961 1966 1971 1976 1981 1986 Figure 1. Lake Michigan water level, 1961-1992 1991 indicates that the 1893-1895 drought may have had as extensive an impact as the 1952-1955 drought in many parts of Illinois. However, there are no streamflow records for this earlier drought. The major difference between a moderate and severe streamflow drought is usually related to the duration of the drought. Since 1965, three shorter droughts are generally considered to have been moderate in nature: 1976-1977, 1980-1981, and 1988-1989. For much of Illinois, the 1988-1989 drought was intense, but lasted less than nine months. But in western and west-central Illinois (the Spoon River at Seville and the LaMoine River at Ripley) this drought started in 1987 and ended late in 1989. For this region of the state, the drought of 1988-1989 was severe, and for several locations it is the drought of record. Number of Communities Having Water Shortages The impact of a drought on a surface water supply sys- tem depends greatly on the source of the supply as well as the intensity and duration of the drought. Systems that obtain water from a low channel dam or by direct withdrawal from a stream are susceptible to any short, intense drought that causes low flow (up to two months in duration). Reservoirs with a great deal of storage (relative to both the average inflow and water use) are designed to supply water for multiyear droughts, and therefore may not be severely impacted by short, intense droughts. Table 3 describes the drought dura- tion that is most critical for selected reservoirs. The impact on surface water supplies is usually preceded by a relatively long period of below-normal precipitation. There is no exact definition of when a
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