Rain and Drought in Virginia

August/September, 2016 streamflow
August/September, 2016 streamflow
Source: USGS Water Watch

The depth and width of stream channels in Virginia have been shaped by the normal flow of water, resulting from the normal runoff from an average year - but rainfall in Virginia on any particular day, or for any particular year, is rarely "average." Averages come from recording rainfall for decades, then doing statistics to derive a reliable pattern.

Across Virginia, the average rainfall is 43" per year, but that varies by location, season, and year. When storms arrive, expect strong winds, heavy rain, damage to human-built infrastructure - and a shift by TV stations into continuous "the sky is falling" crisis coverage, which is an almost-annual routine now.

The worst drought of the 20th Century in Virginia was in the 1930's, the same period of the Dust Bowl in Oklahoma. In 2002, Virginia experienced another record-setting drought that was followed in 2003 by record-setting rainfall.

in 2002, Virginia rivers were at record low flow levels (red dots)
in 2002, Virginia rivers were at record low flow levels (red dots)
in 2003, rivers were at above-average high flow levels (blue dots)
in 2003, rivers were at above-average high flow levels (blue dots)
water levels
Source: US Geological Survey, Water Watch

The Rapidan River went dry in 2002, down to to 1 cubic foot per second (cfs). That forced the water system in the Town of Orange into emergency status. All public restrooms were locked, and portajohns decorated the parking lots of even the fast food restaurants.

Rapidan River record lows
Source: USGS Water Resources, USGS 01667500 RAPIDAN RIVER NEAR CULPEPER, VA

In the 1950's and again in the 1960's, other droughts had lowered the flow of the Rapidan River below 10cfs:

Rapidan flows since the 1930's
Rapidan flows since the 1930's
Source: USGS National Water Information System (NWIS) -
USGS 01667500 RAPIDAN RIVER NEAR CULPEPER, VA

A cubic foot of water is close to the size of a basketball, about 7.5 gallons. When the Rapidan River flow dropped to one cubic foot of water per second (cfs), that means about 7.5 gallons per second were flowing past the river gauge on the Orange County-Culpeper County line.

If every drop of Rapidan River water were diverted to the water system, leaving nothing for the fish in the river and letting them die in the sun, then the Rapidan River flowing at 1cfs could supply only 450 gallons per minute (7.5 gallons per second x 60 seconds in a minute). A single house can use 5 gallons/minute, so the drought was a crisis.

drought in 2002
Source: Drought Monitor - 2002

In 2003, the rainfall was above-average. In October, 2003, Hurricane Isabel showed that flooding is not the only problem with storms. Tree roots in Virginia's saturated soil could not withstand the long period of strong winds. Massive power outages occurred as trees fell on power lines that were not buried underground.

Storms named Gaston and Ivan made September 2004 far wetter than average, and created dramatic flooding in some places. In 2011, the trigger for flooding and power outages was Tropical Storm Lee.

Young's Branch
Young's Branch on Manassas National Battlefield Park at "bankfull" level, before rising higher and flooding adjacent fields (the "floodplain") in August, 2003
rainfall since 1999
patterns of Virginia streamflow in mid-September, since 1999

Youngs Branch in Manassas Battlefield (September 6, 2008)
Youngs Branch in Manassas Battlefield (September 6, 2008)
Youngs Branch one week later (September 13, 2008)
Youngs Branch one week later (September 13, 2008)

Ski operators care about precipitation in the winter. Every day of snow might trigger urban residents to plan ski trips, even if the slopes in Virginia are covered with manufactured snow. Grape growers are sensitive to August/September rains. If harvest time is dry, juice in grapes is concentrated, the sugar percentage increases, and the winemaking is easier. If it rains just before harvest, grapes can absorb so much water they may even split their skins; more skill is required to bring in the grapes and create a great wine from a wet harvest.

Northern Virginia gets lots of rain in the summer from short, intense thunderstorms. In the winter, lightning/thunder is rare and three days of gray, overcast skies are common. At the start of the Spring Semester after the holiday break, students at Virginia Tech in Blacksburg get tired of seeing gray skies above a campus filled with equally-gray limestone buildings.

since 1900, rainfall in Virginia has ranged from 25 inches/year to over 60 inches (average is 43 inches/year)
since 1900, rainfall in Virginia has ranged from 25 inches/year to over 60 inches ("average" is 43 inches/year)
Source: National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center, Climate at a Glance

Droughts and floods are common experiences across Virginia. Land use planners and disaster management specialists pay close attention to development within the 100-year floodplain, the area where there is a 1% chance of a flood at any time, but the potential lack of water is equally serious.

Water distribution has two facets - how Mother Nature provides it, and how humans capture and distribute it. One is a science story, the other is political. Two droughts in 1998 and 2002 were sufficient for the General Assembly to require all localities to create a long-range plan to ensure an adequate water supply consistent with planned population growth.

After the 2002 drought, the General Assembly passed legislation requiring all counties/cities to prepare water supply plans, and to prepare to meet future demand. Regional plans were encouraged, but jurisdictions were allowed to create long-range plans if they chose not to partner with the neighbors.

Some communities proposed new sources of supply, while others emphasized conservation. Charlottesville debated for nearly a decade whether to raise the height of the Ragged Mountain dam, flooding adjacent property, or dredge the reservoir to increase its capacity. In the end, Charlottesville chose to increase supply by building a new dam that was 30' higher, rather than relying upon existing reservoirs and water conservation.

to ensure adequate water supply, the Rivanna Water and Sewer Authority chose to expand the Ragged Mountain Reservoir
to ensure adequate water supply, the Rivanna Water and Sewer Authority chose to expand the Ragged Mountain Reservoir
Source: ESRI, ArcGIS Online

A single year of drought is just a short-term problem. A string of drought years back-to-back can have substantial impact. Studies of tree rings, where the growth of bald cypress trees from southeastern Virginia can be measured back into the 1500's, suggest Virginia's worst drought in historical times occurred... right when the English settlers landed at Jamestown. The saltiness of the water in the summertime at Jamestown peaked then, perhaps debilitating the colonists through subtle, slow salt poisoning.

modern bald cypress tree at Jamestown
modern bald cypress tree at Jamestown
bald cypress knees at James Smith's Fort
bald cypress knees at James Smith's Fort

Starting in 1997, the faucet ran dry again, and Virginia received below-average rainfall for five of the next six years. In 1999, the multi-year drought in southeastern Virginia was interrupted by major flooding from Hurricane Floyd, but the rest of the state continued to suffer.

rainfall was below average statewide between 1997-2002
rainfall was below average statewide between 1997-2002
in September 1998, the Palmer Drought Index showed all of Virginia in moderate to extreme drought
in September 1998, the Palmer Drought Index showed all of Virginia in moderate to extreme drought
Source: National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center, Drought - Summer 1999

Streamflow in the Fall often varies based on a mix of hurricanes and drought:

August/September, 2014 streamflow
August/September, 2014 streamflow
Source: USGS Water Watch
August/September, 2013 streamflow
August/September, 2013 streamflow
Source: USGS Water Watch
August/September, 2012 streamflow
August/September, 2012 streamflow
Source: USGS Water Watch
August/September, 2011 streamflow
August/September, 2011 streamflow
Source: USGS Water Watch

August/September, 2010 streamflow
August/September, 2010 streamflow
Source: USGS Water Watch
2008 rainfall
average Virginia streamflow in mid-September, 2008
2007 rainfall
average Virginia streamflow in mid-September, 2007
2004 rainfall
average Virginia streamflow in mid-September, 2004
2003 rainfall
average Virginia streamflow in mid-September, 2003
2002 rainfall
average Virginia streamflow in mid-September, 2002

Rain Shadows - The Orographic Effect

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