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.