State of the Coast: South Coast

Now in its third year, The Trustees’ annual State of the Coast report pulls together the latest climate change projections to tell the story of what is expected to happen along our Massachusetts coastline. This year we focus on the South Coast and the 14 towns that border Buzzards Bay and Narragansett Bay. Over the next 30 years, this region is projected to experience increased flooding in low lying communities, loss of salt marsh, impacts to water quality, and erosion of shorelines. In producing this report, The Trustees collaborated with towns and partner organizations to develop recommendations for collaboration and action that will lead to resilient communities and natural resources.

This report highlights the projected impacts of rising seas and increasing storm surge on the ecology of Buzzards Bay and Narragansett Bay, as well as quantifies the significant threats to community infrastructure projected in the coming years. Communities along this stretch of coast suffered devastating effects from the 1991 storm surge of Hurricane Bob, one of the costliest storms in New England history [CIT. 1]. Today, they continue to face the intensifying and accelerating results of flooding from sea level rise, stronger storms, and wave energy.

The impacts of sea level rise and increased flooding events vary across this region. This is in part due to the glacially formed coastline, consisting of a patchwork of protruding headlands and associated embayments, intermixed with pocket and barrier beaches [CIT. 2]. Exposed to the open ocean, the towns of Westport and Dartmouth experience more erosion from storms and wave energy. Further up Buzzards Bay, towns are more protected from waves but experience a funnel effect as water can surge up the Bay and intensify flooding at the northern end, impacting low-lying roads and buildings in Wareham and neighboring towns.

In addition to infrastructure, projections show vast losses of coastal salt marshes, erosion of beaches with little room to migrate inland, and water quality jeopardized by rising floodwaters, higher water temperatures, and stormwater runoff. These ecosystems provide habitat to shellfish, fish, and birds that call these bays home but also offer critical protection to our coastal communities by buffering flood waters and wave energy. When natural landscapes deteriorate, so does the resilience of our coastlines.

WHY NOW?

Over the next 30 years, sea levels along the South Coast are projected to rise over two feet [CIT. 3], and storms are expected to be more frequent and intense, if global carbon emissions remain high [CIT. 4]. While this report focuses primarily on these pressures from the ocean, the impacts of climate change may also result in drier summers and more frequent droughts, diminishing snowfall and higher precipitation in winter and spring, and increased inland flooding.

It is urgent that we work together to address the climate change pressures that we are already witnessing in our communities and ecosystems.

Consider:

• Both daily tidal flooding and storm events are projected to inundate low-lying roads and buildings that are not adapted to flooding. In Wareham, due to its location and low-lying infrastructure, more than a quarter of all buildings in town could be inundated by a 10-year storm as soon as 2050 [CIT. 5].

• Daily tidal flooding alone is projected to impact over 25 miles of roadway and over 1,400 buildings across the region as soon as 2050. A 10-year storm could impact over 15,000 structures and over 250 miles of roadway by 2050 [CIT. 5].

• Rising seas are projected to drown out salt marsh earlier than other regions of the state with a 23% loss of marsh as soon as 2050 [CIT. 6].

• Existing development threatens the ability of coastal beaches and salt marshes to migrate inland with sea level rise, putting them at risk of loss.

• The hurricane barrier, built in 1966 to protect the Port of New Bedford from storms, is projected to close more frequently in the future due to high tides alone. Closing the barrier at the same water level as is done currently would mean 1–2 closures a day as soon as 2050. For comparison, the barrier closed a total of 26 times in 2019 [CIT. 7].

• Rising water temperatures and increased stormwater runoff may further impact water quality. Excess nutrients have contributed to the loss of 43% of Buzzards Bay eelgrass beds over the last 30 years [CIT. 8], resulting in major declines in populations of bay scallops and other shellfish [CIT. 9].

It may feel like the challenges facing us are too enormous to confront. But by thinking across town boundaries and sharing strategies, solutions, and outcomes of pilot projects, we can start to move the needle. The work of nonprofit organizations together with towns, agencies, and landowners to reduce nutrient inputs to the bay over the last 20 years is already a success story and model to follow. The need for broader regional collaboration such as this along the South Coast to prepare for and mitigate the coastal effects of a changing climate is clear, as is the urgent need for greater resources to make that happen.

WHY US?

As the largest private coastal landowner and first land conservation nonprofit in Massachusetts, The Trustees has witnessed firsthand the widespread effects of climate change up and down the coast, from the compromised salt marshes and habitats of Old Town Hill in Newbury to the shifting dunes and barrier beaches of the Coskata-Coatue Wildlife Refuge on Nantucket. We are in a unique position to share a long-term perspective that speaks to our mission, values, and philosophy — and underscores the urgent need for new coastal strategies and regulatory reforms.

For us, protecting the coast is not only a priority — it’s part of who we are. We strive to be a champion for these iconic landscapes of extraordinary ecological and recreational value — all vulnerable to change. In partnership with local stakeholders, now is the time for bold, coordinated adaptations to climate change.

WHAT DATA DID WE USE?

The Trustees and the Woods Hole Group, Inc. utilized results from the Massachusetts Coast Flood Risk Model (MC-FRM) [CIT. 5, 11] to investigate future scenarios of tidal and storm based flooding extents and threats to infrastructure (roads and buildings) as soon as 2030, 2050 and 2070. MC-FRM includes sea level rise (SLR) associated with the “high” projections as recommended by the Massachusetts Office of Coastal Zone Management (CZM) and the University of Massachusetts and developed specifically for the Commonwealth of Massachusetts by DeConto and Kopp (2017) [CIT. 3]. This “high” scenario of SLR provides an estimate that is extremely unlikely to be exceeded with continued high global emissions and projects 1.3 ft, 2.6 ft and 4.4 ft of rise above a 2008 baseline year as soon as 2030, 2050 and 2070, respectively [CIT. 3]. By using these sea level rise projections, the findings presented herein are consistent with the Commonwealth’s climate change planning tools used by state agencies [CIT. 12].

Projected impacts to tidal marshes and coastal habitats were derived from the Sea Level Affecting Marshes Model (SLAMM) results developed for CZM by Woods Hole Group [CIT. 6]. The SLAMM results were developed using the latest sea level rise projections available at the time of that study [CIT. 13]. The “high” scenario used for this report is a little lower than the more recent projections of DeConto and Kopp (2017).

Sea level rise projections released by the National Oceanic and Atmospheric Administration in 2022 (NOAA) [CIT. 14] are lower than the “high” projections used to model coastal flooding in this report. For example, the value for sea level rise by 2050 under the “high” scenario used by Woods Hole Group for this report (using an 83% confidence interval or 17% chance of underpredicting) is 0.5 feet higher than the NOAA projection. Through consultation with NOAA and CZM, we decided to continue using the same MC-FRM and SLAMM results since they provide greater certainty of identifying impacts that need to be addressed — important when expending significant resources on adaptation and resilience projects.