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Needed Rain Helps Avert a Drought in May

U.S. Department of the Interior
U.S. Geological Survey

Wendy McPherson (
Maryland-Delaware-D.C. Water Science Center
5522 Research Park Drive
Baltimore, MD 21228
FAX: (443)498-5510

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Updated: June 6 , 2001

Streamflow levels declined in early May across Maryland and Delaware and in the Chesapeake Bay, but were improving at the end of the month because of heavy rain, according to hydrologists at the U.S. Geological Survey (USGS) in Baltimore, Maryland. The National Weather Service reported 5.34 inches of precipitation during May at BWI Airport, which was 1.62 inches above normal. This rainfall has helped to recharge the Groundwater levels and to maintain water storage in the Baltimore reservoir system at 99 percent of capacity, but seasonal rainfall is needed to keep streamflow levels from declining again.

Streamflow entering the Chesapeake Bay averaged 33.1 bgd (billion gallons per day) in May, which is 46 percent below the long-term average for May, and streamflow from the Susquehanna River into the Bay was the lowest since May 1941 (see graphs at: Streamflow in May represented a 48-percent drop from April, and continued a year of having below average streamflow into the Bay for every month except April. Low streamflow has resulted in increased salinity levels in the Bay. The higher salinity levels may cause oysters to suffer because of greater incidence of diseases Dermo and MSX, which are prevalent in high salinity years. The low flow may also mean lower amounts of nutrients entered the Bay during the spring. This would be beneficial since high amounts of nutrients and sediment can lead to poor water-quality conditions for many of the Bay's living resources.

Streamflow of the Potomac River near Washington, D.C., also decreased from April, and was 45 percent below the long-term average for May. The monthly streamflow levels at five USGS index stations were all below normal in May; however, streamflow on the Choptank River near Greensboro, Maryland, on the Eastern Shore was only 5 percent below normal.

Groundwater levels in water-table wells at the end of May were mostly in the normal range for Delaware and Maryland (see graphs at: Groundwater levels in water-table wells typically decrease in the spring and summer as more water is consumed by evapotranspiration from growing plants and increase air temperatures.

As the Nation's largest water, earth and biological science, and civilian mapping agency, the USGS works in cooperation with more than 2,000 organizations across the country to provide reliable, impartial scientific information to resource managers, planners, and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, contribute to the sound conservation and the economic and physical development of the Nation's natural resources, and enhance the quality of life by monitoring water, biological, energy, and mineral resources.

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