Northern Virginia is usually a fairly wet location. It rains about 44 inches a year on average. However, that is on average. The DC metro region has not had rain in 32 days. According to the ICPRB the region’s longest dry streak was in 2007 and ran 34 days. At this time, no appreciable rainfall is expected in the next week so it looks like we’re going to break the record.
“A wide range of evidence indicates that the earth has been warming over the past century, causing glaciers and sea ice to melt in many parts of the world, sea levels to rise, and patterns of precipitation to change. Most scientists agree that these trends are likely to continue and to accelerate due to increasing levels of carbon dioxide and other “greenhouse” gases in the atmosphere. Likely changes in temperatures and precipitation will
affect the availability, use, and management of water resources.”
“According to projections from climate models, temperatures
in the Potomac basin will rise whereas precipitation could rise or fall. Both
temperature and precipitation have an impact on stream flows, and the range of
available climate projections lead to a wide range of potential changes in
water availability in the basin.”
"The primary climate models have predicted it is likely that
storms will be more intense and droughts will be longer and more severe going
forward. “Results project changes in long-term average summer basin-wide stream
flows ranging from -35 percent to +42 percent, with a median of +2 percent,
over the period between 1995 and 2040.” The region has been preparing for this
variability by building billions of gallons of water storage still years away
from being completed.
On a positive note, the upstream drinking water reservoirs that we have in service are nearly full. These reservoirs would be used to supplement downstream flow in the case of a severe drought. The region has been planning for water supply shortages for years. The extended dry conditions have increased the area of Moderate Drought Conditions (D1) in the Potomac River watershed by almost 30% since last week alone. ICPRB staff is monitoring the river’s flow and keeping in contact with the region’s stakeholders. Due to low flow conditions and no rain in the forecast in the next 10 days it is expected that ICPRB will begin Drought Monitoring any day now.
The impacts from Tropical
Storm Helene at the end of September hit the region with a excess precipitation
a month ago. Since then, above-average temperatures and little precipitation
have led to decreases in soil moisture for much of the Commonwealth as well as
slight decreases in streamflow. Gages throughout much of Virginia monitoring
network (which excludes the Potomac Watershed) indicate normal levels.
Groundwater levels in most of the Commonwealth remain low and continue to
exhibit seasonal and drought related declines, with Northern Virginia and
Shenandoah regions reading less than the 5th percentile in groundwater. The
8-14 day weather forecast predicts normal to above normal temperatures and
chances of slightly below average precipitation.
The most recent weekly U.S. Drought Monitor (USDM) web page
map for Virginia (released October 31, 2024) showed abnormally dry (D0)
conditions mapped across approximately 90.00 % of the Commonwealth and moderate
drought (D1) conditions mapped across approximately 13.45 % of the
Commonwealth. This is a significant increase from the previous week as the
effects of the Tropical storms of September fade.
