From 2013 to 2018, Maryland saw a decline in tree cover and an increase in impervious surfaces across the Chesapeake Bay watershed, according to a new report by the Chesapeake Bay Program.
The news comes from recent analysis of land use and land cover data from the Chesapeake Bay Program’s Very-High Resolution Land Use/Land Cover and Change Data. The report compared data gathered in 2017/2018 to data gathered in 2013/2014.
The report showed that 1,927,940 acres (3,012.4 square miles) throughout the watershed are covered by impervious surfaces, including roads, parking lots, rooftops, and other surface that water cannot pass through. That’s an increase of 50,651 acres (79.1 square miles). This nearly 2 million acres makes up 4.75% of the entire land area of the Bay watershed.
Buildings and other structures made up 31.6% of this net increase, and roads contributed 4.2%. The highest portion of the increase — 64.3% — came from construction of driveways, parking lots, runways, and rail lines. The category also includes areas currently in development, such as acres cleared for construction.
The new data also reveals a loss of tree canopy across the Chesapeake Bay region. More than 8,000 acres of trees have been planted between 2013 and 2018, but over 25,000 acres of tree canopy has been lost in community areas, which the U.S. Census defines as “municipalities, cities, towns, villages, and boroughs.”
“Impervious surfaces contribute to stormwater runoff which can transport nutrients, toxic chemicals, road salts and sediments to streams, alter stream flow and increase water temperature,” said Peter Claggett, coordinator for the Chesapeake Bay Program Land Use Workgroup and a research geographer with the U.S. Geological Survey. “Stormwater runoff is the fastest growing source of pollution to the Chesapeake Bay. Mapping impervious surfaces and monitoring how they change over time are critical for managing runoff and restoring streams and watersheds.”
With the decrease of Maryland’s tree canopy comes a loss of a tool to help reduce dangerous heat and flooding.
“Extreme heat and more intense flooding are directly related to changes in climate. Tree canopy—particularly over asphalt—can help cool our streets and reduce flooding in a cost-effective way,” said Ann Jurczyk, chair of the Land Use and Conservation Subcommittee of the Chesapeake Bay Program. “This high-resolution data from the Chesapeake Bay Program enables localities to review and potentially change their programs and policies to preserve existing canopy and fill canopy gaps in an equitable manner.”
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Maryland, Pennsylvania, and Virginia planted the highest number of trees in community areas between 2013 and 2018 at 6,501; 916; and 445 acres respectively. Washington, D.C. planted 359 acres over the same period. Delaware, New York, and West Virginia planted 14, 40, and 33 acres of trees respectively, though they contain a much smaller portion of the Chesapeake Bay watershed compared to the other four jurisdictions.
Though Maryland reported the greatest cumulative community tree planting at nearly 86% of the total reported acres across the watershed, it also showed the greatest net loss at 4,537 acres.
The Chesapeake Tree Canopy Network website has many fact sheets created that explain the breakdown of land use and land cover in each county, including net gain or loss.
“Chesapeake Bay scientists recently cautioned that after four decades of effort, water quality has improved in some areas of the Bay but in other areas not to the degree anticipated. While their report was sobering, it also presents an opportunity to more fully adopt promising approaches to restore the Bay,” said Joel Dunn, president and CEO of the Chesapeake Conservancy. “Data and technology can inform and empower the Chesapeake conservation movement like never before. In this case, land use decisions in the watershed will finally be informed by both the amount and the value of tree canopy status in every county, one of the most significant factors for water quality.”
