The rate of land conversion is largely determined by socioeconomic, demographic and cultural factors such as job growth, housing and office space availability, housing affordability, population age structure and cultural preferences. Population growth encapsulates many of these factors and is useful for interpreting the conversion of forests and farms to development. 

Monitoring population is particularly useful for interpreting changes in impervious cover. Expansion of impervious surfaces is most prevalent in suburban counties adjacent to cities. Most of these counties have experienced growth for decades and have the infrastructure and resources to support well-informed land use decisions. These counties will be at the top of any list quantifying changes in impervious cover. However, when these estimates are normalized by population growth (e.g., impervious acres per capita), they often fall to the bottom of the list. Bay Program partners are trying to encourage the accommodation of population growth while minimizing increases in impervious cover and resultant losses of forests, farmlands and wetlands.  

As of 2024, 18,939,191 people were estimated to live in the Bay watershed, slightly up from 18,603,560 in 2021. The long-term trend is a large increase; from 1950 through 2024, the Bay watershed’s population has increased from 8,379,276 to 18,939,191. Population projections through 2050 predict a further increase in population, but at a slower rate than in previous decades. Population changes vary regionally within the watershed; some areas have continued to experience population growth, while others are leveling out or declining.

The way humans use the land has a dramatic impact on the Bay and local waterways. The decline in the health of the Chesapeake Bay is correlated to the rise in population in the watershed from 1950 through the 1980s. Experts predict that the watershed’s population will increase to almost 22 million by the year 2050, with related loss of natural areas and increases in urban development. While the rate of growth is expected to decline over the coming decades, absolute growth is expected to continue to exceed 1 million people per decade. This increase in human population and its effects are expected to pose new challenges for 20 of the 31 outcomes in the 2014 Chesapeake Bay Watershed Agreement that list land use change or land conversion as an important factor influencing progress. 

Our partners have invested more than $3 million in land cover data. While the cost of future data development efforts may fall with improvements in instruments, imagery and classification techniques, these costs could still be considerable.

The sustainability of long-term monitoring is a question of political will. Fiscal constraints could impact the temporal and spatial scale at which we assess land cover change. Monitoring every two to three years will require more funding, but monitoring every four to five years may not provide resource managers or elected officials with the timely information needed to support new policies.

Addressing this outcome will require metrics that account for the conversion of forests, farmland and wetlands and for changes in impervious cover. Each type of conversion presents unique monitoring challenges. Wetlands, for instance, cannot be accurately mapped with only the leaf-off and leaf-on aerial imagery typically collected by state and federal agencies. While techniques that use high-resolution data to assess landscape change with the precision needed to inform county-level decisions have advanced, they are not sufficiently established to distinguish between persistent and ephemeral changes in land cover.

Techniques to quantify the social and environmental impacts of land conversion must be explored and developed. Examining impacts to water quality, for instance, may require different approaches for nitrogen, phosphorus and sediment. Examining impacts to wildlife habitat may require regional habitat assessments for keystone species, species guilds or particular species of concern. Examining social and economic impacts will perhaps be the most challenging. Land conversions (other than those caused by extreme weather events) are often motivated by private and public interests, and their impacts are often characterized as overwhelmingly positive by the time they occur. Identifying negative impacts to the environment or to under-represented or at-risk communities challenges the status quo and risks becoming politicized.