Item talk:Q71237

Low streamflow conditions in Washington, Oregon, and Idaho during water year 2001

Below-normal precipitation levels and abovenormal temperatures across most of the Columbia River Basin in the Pacific Northwest (Washington, Oregon, and Idaho) resulted in streamflows that, at times, approached long-term minimums. The period from October 1, 2000, through September 30, 2001 (water year 2001), was the second driest on record (1895–2001) for the three-State area. In addition, average temperatures during the April through September 2001 period were the twelfth highest since 1895. Conditions in the part of Canada included in the Columbia River Basin were similar. Streamflow levels at several locations approached those during water year 1977, when several minimum-flow records were set. The drought of 1977 commonly is considered the drought of record in the region. Low streamflows were most noticeable in rivers east of the Cascade Range, where most of the streamflow above base flow is a direct result of snowmelt runoff. Because of below-normal precipitation across the region, snowpack levels in the three States were only about 59 to 62 percent of the long-term (1961–90) average. Miscellaneous low-flow measurements were made at more than 700 locations across the three- State region and in some adjacent States. These measurements were made in late summer and early fall of 2001 during base-flow conditions. In general, these low-flow measurements were similar to those made at the same locations during water year 1977. Reservoir storage values for seven major river basins in the three-State region were all below the 30-year average at the end of water year 2001. Reservoir storages were at average levels at the end of water year 2000; thus, the below-average levels in water year 2001 can be related directly to low streamflows during water year 2001. Near the end of water year 2001, the Palmer Drought Severity Index ranked much of the region in the severe or extreme drought categories. Only the coastal area of Washington and Oregon and part of the mountain region in Idaho were in the near-normal category. The National Oceanic and Atmospheric Administration classified most of the area as exhibiting adverse agricultural, hydrological, and fire-danger effects from the drought. Lack of available water for recharge and increased pumpage needed to augment the reduced surface-water supply likely reduced ground-water levels throughout the region. Twenty-five wells across the region were selected for extended monitoring to help define the possible short- and longterm relation between low streamflows and ground-water levels.