Recent Progress: Increase

This outcome has made tremendous progress over the past two years, including the finalization of a high-resolution land use/land cover (LULC) data set for all counties within and adjacent to the Chesapeake Bay watershed, for the years 2013/14 and 2017/18. These data have been incorporated into an impervious surface cover indicator for this outcome, representing an increase in recent progress for this outcome as it directly improves our knowledge of land conversion. In 2024, the high-resolution LULC data will be used to inform additional indicators, such as rates of land conversion, riparian forest extent and change, and effective impervious cover extent and change. Efforts are also underway to back-cast the high-resolution LULC data from 2013 to the 1980s.

Outlook: On Course

The Land Use Methods and Metrics Development Outcome is on course. The development of an impervious surface cover indicator enables reporting on the amount of the watershed covered by impervious surfaces, the change in impervious cover over time, and the types of impervious cover that contributed most to the changes. The remaining metrics described in the outcome language will be finalized and released in 2024 with additional data for the years 2021/22. Current funding covers the monitoring of land change through 2021/22, enabling the completion of that work. However, no additional funding has been allocated to continue monitoring land change in the future, as called for in the outcome. Apart from funding, the part of the outcome that poses the greatest challenge currently is translating the LULC change data into a form that is actionable for communities, which will require closer coordination among teams working on related outcomes.

In 2017/18, there were 3,003.8 square miles of impervious cover in the Bay watershed, representing 4.75% of the land area (63,354 square miles) that water cannot pass through (e.g., roads, parking lots, rooftops). Over the period from 2013/14 to 2017/18, impervious cover increased by 79.1 square miles, a 2.6% relative increase and an absolute increase of 0.12% as a percentage of land area. The Chesapeake Bay basin consists of 86,974 sub-watersheds, areas that drain to the most downstream point within each catchment (the immediate area that drains to a particular section of stream) in the data set. Few of these sub-watersheds exhibited significant increases (>=3%) in impervious cover during the measured timeframe; most of these being headwater sub-watersheds of less than 3,500 acres (due in part to their small size) and mostly in Virginia. Suburban areas around major cities such as Harrisburg, Baltimore, Washington D.C., and Richmond are among the fastest developing land areas, with the potential for adverse effects on local waterways.

Structures contributed to 31.6% of the net increase in impervious surfaces, while roads contributed to only 4.16% of the increase. Other impervious surfaces (e.g., driveways, parking lots) contributed to most of the net increase at 64.25%. This category includes interim stages of development, such as areas that are cleared for construction but may ultimately fall into one of the other categories when construction is complete.

This interactive map shows the impervious surface cover in the sub-watersheds of each tributary within the larger Chesapeake Bay watershed, highlighting changes between the time periods measured as well as the baseline impervious cover in 2013/14. Negative percentages of impervious cover change indicate a decrease in impervious cover in that area. To focus on more significant changes, minimal changes between -.1% and .1% are not shown.

Forests, farms and wetlands provide valuable ecosystem services. These landscapes produce food, improve water quality, provide wildlife habitat and give us opportunities to have fun in the natural world. Monitoring the conversion of these natural and working landscapes is critical to minimizing the extent and mitigating the effects of the land conversion process. Impervious surface cover is the first developed indicator for reporting progress toward the Land Use Methods and Metrics outcome and the underlying data will be used to inform the Water Quality, Healthy Watersheds, and Tree Canopy Outcomes with potential to also inform the Stream Health and Climate Resiliency Outcomes.

Learn About Factors Influencing Progress

Management Strategy

To achieve this outcome, Chesapeake Bay Program partners have committed to:

  • Monitoring the conversion of farmland, forests and wetlands at least every four to five years.
  • Assessing the rate of impervious surface change at least every four to five years.
  • Quantifying the impacts of land conversion on water quality, healthy watersheds and communities.
  • Communicating results to the public, elected officials and Chesapeake Bay Program partners.

Assessing progress toward the outcome will occur on a semi-annual basis. Once metrics and impact measures are approved, they will be reassessed with the receipt of updated LULC information at least every four to five years.

As part of the Chesapeake Bay Program’s partnership-wide implementation of adaptive management, progress toward this outcome was reviewed and discussed by the Management Board in March of 2023.

Download Management Strategy (.pdf)

Logic & Action Plan

Chesapeake Bay Program partners have committed to taking a series of specific actions that will support the management approaches listed above.


  • Developing additional metrics and supporting measures for tracking land conversion, such as effective impervious cover change (factoring in the impact that even a small impervious area may have when directly connected to streams via proximity, storm drains or other conduits); forest, farmland, and wetland conversion to developed lands; and riparian tree cover change.

  • Linking the results of analyses completed as part of the Land Use Methods and Metrics Development Outcome to the work being done toward the Land Use Options Evaluation Outcome.

  • Initiating a new five-year cooperative agreement to continue monitoring LULC change through the year 2029,
  • Providing LULC data for the next version of CAST.
  • Overseeing a GIT-funded project on Community Response to LULC change.

Recently Completed

2022 – 2023

  • Finalized an impervious cover change metric to inform the Land Use Methods and Metrics Outcome.
  • Finalized and published the 2021/22 LULC data along with updating and reissuing the 2013/14 and 2017/18 LULC data.
  • Finalized and published the hyper-resolution hydrography data.
2020 – 2022
  • Incorporated draft one-meter resolution LULC change data from 2013/14 to 2017/18 into CAST-21 to assess impacts of land change on water quality.
  • Finalized and published the 2017/18 and 2013/14 LULC data and incorporated it into the Chesapeake Healthy Watershed Assessment to assess impacts to state-designated healthy watersheds.
  • Incorporated land use change forecasts from the Chesapeake Bay Land Change Model to assess the vulnerability of state-designated healthy watersheds to land conversion.
  • Developed a Community Tree Cover Indicator based on the one-meter LULC change data.
  • Developed county-level tree cover change fact sheets.
  • Developed fact sheets, story maps and other communication tools to educate and inform the public about the high-resolution data.
  • Published floodplain and stream channel metrics.
  • Reviewed draft hyper-resolution hydrography data for select areas of the watershed.

Learn About Logic & Action Plan

Participating Partners

The Healthy Watersheds Goal Implementation Team leads the effort to achieve this outcome. It works in partnership with the Vital Habitats, Water Quality and Fostering Stewardship goal implementation teams, as well as the Local Government Advisory Committee.

Participating partners include:

  • District of Columbia Department of Energy and Environment (District of Columbia)
  • Delaware Department of Natural Resources and Environmental Control (State of Delaware)
  • Maryland Department of the Environment (State of Maryland)
  • Maryland Department of Planning (State of Maryland)
  • Montgomery County Department of Environmental Protection (State of Maryland)
  • Pennsylvania Department of Community and Economic Development (Commonwealth of Pennsylvania)
  • Pennsylvania Department of Conservation and Natural Resources (Commonwealth of Pennsylvania)
  • Pennsylvania Department of Environmental Protection (Commonwealth of Pennsylvania)
  • New York Department of Environmental Conservation (State of New York)
  • Virginia Department of Conservation and Natural Resources (Commonwealth of Virginia)
  • Virginia Department of Environmental Quality (Commonwealth of Virginia)
  • West Virginia Department of Environmental Protection (State of West Virginia)
  • Chesapeake Bay Foundation
  • Chesapeake Bay Commission
  • Chesapeake Conservancy
  • U.S. Environmental Protection Agency
  • U.S. Geological Survey