Water-Resources Investigations in Wisconsin, 2001

Abstract

The statewide average precipitation of 32.82 inches for the 2000 water year was 1.14 inches greater than the normal annual precipitation of 31.68 inches for water years 1961-90. Average precipitation values affecting streamflow conditions ranged from 90 percent of normal in northwest Wisconsin to 121 percent of normal in southeast Wisconsin (summary tables provided by Lyle Anderson, State Climatology Office, University of Wisconsin, Madison, written commun., 2001). Although precipitation for the year averaged only 104 percent of normal, the 2000 water year had extremes of beginning dry, turning very wet in the spring, and ending dry again. The year began below normal the first quarter of the year in all climatic divisions of the State. Record high temperatures in February and March and below normal snowfall brought an early spring and dry conditions statewide during March and April (Wisconsin Agricultural Statistics Service, 2000). The northern part of the State was still below normal for May. May and June brought record wet weather and cool temperatures for the southern half of the State: southeast Wisconsin received over 270 percent of normal rainfall for May, and southwest Wisconsin received over 250 percent of normal rainfall for June. June was the wettest month statewide, averaging 173 percent of normal. The last quarter of the year was more variable with the northern half of the State being below normal and the remainder near normal; heavy rains exceeding 10 inches for the month occurred in localized areas during July and September. Runoff differed for rivers throughout the State and ranged from 33 percent in east central Wisconsin to 166 percent in south central Wisconsin. Runoff was lowest (33 percent of the average annual runoff from 1964- 2000) for the Lake Michigan tributary Kewaunee River near Kewaunee, and highest (166 percent of the average annual runoff from 1974-2000) for the Pheasant Branch at Middleton station in south central Wisconsin. Departures of runoff in the 2000 water year as a percent of long-term average runoff in the State (determined using stations with drainage areas greater than 150 square miles and at least 20 years of record) are shown in Figure 4.