. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. STREAMFLOW CONDITIONS. FLOODING. AND LOW FLOWS 60 Annual Precipitation ,, .yr moving averages. 1915 1925 1935 1945 1955 1965 1975 1985 Figure 1. Comparison of annual precipitation and streamflow, Embarras River watershed near Charleston. climatic conditions. For this reason, it is desirable to use long-term streamflow records to examine trends that may be associated with climatic change. Previous St
. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. STREAMFLOW CONDITIONS. FLOODING. AND LOW FLOWS 60 Annual Precipitation ,, .yr moving averages. 1915 1925 1935 1945 1955 1965 1975 1985 Figure 1. Comparison of annual precipitation and streamflow, Embarras River watershed near Charleston. climatic conditions. For this reason, it is desirable to use long-term streamflow records to examine trends that may be associated with climatic change. Previous Studies Ramamurthy et al. (1989) and Singh and Ramamurthy (1990) examined the increases in average annual flows and peak flows observed on the Illinois River for the period 1941-1985. These studies found that average annual flow on the Illinois River had increased by 20 to 25 percent since 1970, and that annual peak flows had increased about 50 percent. The number of days having high-flow conditions doubled during that time. These studies concluded that the higher flows were caused by concurrent increases in precipitation amounts through- out much of the Illinois River basin. Changnon (1983) examined trends in the number of flood events and the duration of flood flows for 11 large watersheds in Illinois over the period 1921-1980. Changnon concluded that the number of flood events and flood days generally increased over that period, particularly in the northern and eastern portions of Illinois. Changnon also found an increase in the num- ber of heavy rainfall events during the summer (May to August), which is believed to be one of the causes for the increase in summer floods. Gaging Records Used in the Analysis The streamgage records used to analyze the impact of climate variability on hydrology should come from watersheds relatively unaffected by human-induced impacts, including withdrawals, return flows, reser- voirs, detention storage, and major land-use changes. Additional gag
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