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April 2016 Water Conditions Summary

Below average precipitation throughout much of the Mid-Atlantic region resulted in over 50 percent of groundwater levels and monthly mean streamflows being below normal. In April, 54 percent (15 of 28) of groundwater levels at USGS observation wells were below normal and 64 percent (21 of 33) of the monthly mean streamflows were below normal at sites used to monitor the response of water resources to changes in climatic conditions in Maryland, Delaware, and the District of Columbia.

Graph showing percentiles for monthly water conditions

Groundwater was above normal at two USGS observation wells in Baltimore County, Maryland and normal (between the 25th and 75th percentiles) in 39 percent (11 of 28) of USGS observation wells in April.

Monthly mean streamflow dropped at 31 of the 33 streamgages used to monitor climatic conditions, although streamflows typically decrease this time of year until about the end of the September. Streamflow was in the normal range at 36 percent (12 of 33) of USGS streamgages.

*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.

To view more detailed information about Monthly Water Conditions in Maryland, Delaware, and the District of Columbia, use the navigation menu on the left.

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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.

 


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