Water Science for Maryland, Delaware and the District of Columbia
March 2016 Water Conditions Summary
In the Mid-Atlantic region, precipitation was about half of the average monthly precipitation for March and average monthly temperatures were up to 8.8 degrees Fahrenheit above normal. Streamflow responds more quickly than groundwater to climatic conditions, and these weather conditions brought many water levels down from the high February levels that were affected by snowmelt. Monthly mean streamflow dropped at all 33 streamgages used to monitor climatic conditions, and more than half of the sites had below normal monthly mean streamflows.
Although all 33 of the March monthly mean streamflows, and groundwater levels at 19 of the 27 observation wells were less than they were in February, 63 percent (17 of 27) of the groundwater levels and 48 percent (16 of 33) of the monthly mean streamflows were normal (between the 25th and 75th percentiles) at sites used to monitor the response of water resources to changes in climatic conditions in Maryland, Delaware, and the District of Columbia. Groundwater levels were above normal at five wells and below normal at five wells.
*A percentile is a value on a scale from 0 to 100 that indicates the percent of a distribution that is equal to or below it. A percentile between 25 and 75 is considered normal. For example, a groundwater level in the 90th percentile is equal to or greater than 90 percent of the values recorded for that month.
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Why is it important for the USGS to collect and analyze water resources data?
USGS water data are valuable to the public, researchers, water managers, planners, and agricultural users, especially during floods and droughts. These data can be used to assess how water resources respond to changes in climate. Scientists at the USGS have measured streamflow and groundwater levels in wells to assess water resources for over 125 years.
In addition to providing the most extensive set of historical streamflow and groundwater data available to the public, the USGS collects water data and quality-assures the data by employing standardized techniques across the country. The uniformity of the dataset allows for multi-state comparisons and other comparative statistical analyses that better inform policy makers of the possible water resource conditions they might encounter in the future.
The sites used in this water summary were carefully selected to show the response of streamflow and groundwater levels to precipitation. Ideally, these sites will show minimal effects from human influences. The streamflow and groundwater data are ranked in comparison to the historical record and summarized. Precipitation and reservoir data are also presented to give a more complete picture of the region’s water resources.