Key Points adapted from the Fourth National Climate Assessment; Chapter 20

• Coasts are a central feature of Caribbean island communities. Coastal zones dominate island economies and are home to critical infrastructure, public and private property, cultural heritage, and natural ecological systems.
• The way land is used across island watersheds has an observable effect on the coastal, aquatic, and marine communities downstream of them. Climate change impacts on land will have environmental consequences along the coast and beyond.
• Freshwater is critical on islands, yet the Caribbean region is projected to receive less rainfall in the coming decades. Also, saltwater intrusion into freshwater aquifers—due to sea level rise—will reduce the availability of freshwater stored in the ground.
• Sea level rise, combined with stronger wave action and higher storm surges, will worsen coastal flooding and increase coastal erosion. Sea level rise can change beach areas, damage storm surge barriers, and decrease tourism.
• As maximum and minimum temperatures increase, there are likely to be fewer cool nights and more frequent hot days (fewer comfortable days) in the region.
• In 2017, Hurricanes Irma and Maria significantly damaged human infrastructure and changed coastal environments across the U.S. Caribbean. Changes in the frequency and intensity of storms can drive changes in the islands’ natural systems.
• Adaptive planning and nature-based strategies, combined with active community participation and traditional knowledge, are beginning to be deployed to reduce the risks of a changing climate.

The U.S. Caribbean

• For the most recent vulnerability assessment of the region, explore Puerto Rico’s State of the Climate report published by Puerto Rico's Climate Change Council in September 2022.

The U.S. Caribbean territories of Puerto Rico and the U.S. Virgin Islands (USVI) are beautiful places rich in biodiversity, cultural heritage, and natural resources. The Commonwealth of Puerto Rico—Puerto Rico's formal name—includes the main island of Puerto Rico, Vieques, and Culebra, along with the smaller islands of Mona, Monito, and Desecheo. The combined population is nearly three and a half million people. The USVI includes the islands of St. Croix, St. Thomas, St. John, Water Island, and Hassel Island, as well as numerous smaller islands; this territory has a combined population of more than 100,000 people. In addition to the principal islands, the U.S. Caribbean includes more than 800 smaller islands and cays, diverse cultural and historical resources, and a rich array of marine and terrestrial ecosystems. All of the inhabitants depend on the region's natural resources and environmental services for their well-being, livelihoods, local economies, and cultural identities.

Puerto Rico and the USVI have distinct differences in topography, language, population size, governance, natural and human resources, and economic capacity. However, both are highly dependent on natural and built coastal assets. The region's physical geography includes nearshore and open ocean marine areas; coastal wetlands, tropical forests, hills, plains, and interior mountains. Average rainfall amounts vary widely across the region, and social and ecological systems are diverse. 

Exposed assets

San Juan, PR features a dense urban city that converges with the coastline. These built assests are vulnerable to sea level rise, storm surge, and flooding.

Beaches are among the main tourist attractions, and they are exposed to sea level rise and erosion. In Puerto Rico, critical infrastructure such as drinking water and sewer pipelines and pump stations, wastewater treatment plants, and power plants are vulnerable to the effects of sea level rise, storm surge, and flooding. In the USVI, infrastructure and historical buildings are in the inundation zone for sea level rise. Exposed assets include the power plants on both St. Thomas and St. Croix; schools; housing communities; the towns of Charlotte Amalie, Christiansted, and Frederiksted; and pipelines for water and sewage. Critical cargo ports, ferries, and cruise-ship terminals are at risk from extreme weather and climate-related events and are also vulnerable to sea level rise. Main airports in San Juan, Puerto Rico and St. Thomas are also in the coastal zone. 

Island challenges

In general, islands are more exposed to the impacts of climate change than mainland areas:

• Most island residents and visitors depend on regular imports of goods such as food and fuel. Weather and climate-related events anywhere in the global supply chain can disrupt the transport of raw materials and/or products to and from islands.
• Though surrounded by an ocean of salt water, islands have a critical dependence on local sources of freshwater. Higher temperatures and lower total rainfall projected for the coming decades will reduce the availability of freshwater while demand for it increases.
• Sea level rise, coastal erosion, and the impacts of coastal storms threaten critical infrastructure. When roads, power, and water & sewer services are disrupted, jobs that depend on them disappear, damaging local economies. 
• Warming ocean waters and ocean acidification are degrading coral reefs and putting critical marine resources at risk. Changes threaten valuable fisheries and the livelihoods of all those who work to catch, process, package, and deliver fish products.

Differences from the mainland

Changing climate and weather patterns interacting with human activities are affecting land use, air quality, and resource management and are posing growing risks to food security, the economy, culture, and ecosystem services. Puerto Rico and the USVI share many vulnerabilities with coastal states and the Pacific Islands, yet they lack much of the adaptive capacity available to locations within the continental United States. The islands also have unique issues related to data availability and the capacity to develop datasets comparable to those available for the continental United States. For example, the small size of the islands, particularly the USVI, affects the availability and accuracy of downscaled climate data and projections. Additionally, differences in the availability of information and natural and social systems in the region affect the degree of vulnerability to climate change and extreme climate events. These differences are reflected in the needs, priorities, and approaches to reducing climate vulnerability between Puerto Rico and the USVI. 

Changing Patterns

An aerial view of the island of Puerto Rico with 100km gridline context is compared to an annual precipitation map of Puerto Rico. Regional climate models cannot resolve or ‘see’ local topography, land cover, or island climates.

Historically, the U.S. Caribbean region has experienced relatively stable seasonal rainfall patterns, moderate annual temperature fluctuations, and a variety of extreme weather events, such as tropical storms, hurricanes, and drought. However, these patterns are changing and are projected to be increasingly variable as humans produce more heat-trapping gasses and they accumulate in the atmosphere. Having evolved within historic climate conditions, and given the small size and relatively isolated nature of these islands, Caribbean social, economic, and ecological systems are likely to be more sensitive to changes in temperature and precipitation than similar systems in the mainland United States. 

Global climate, local impacts 

The vulnerability of the U.S. Caribbean region to climate change is influenced by global, regional, and local factors. The region is sensitive to large-scale patterns of natural variability in both the Atlantic and Pacific tropical basins, such as the El Niño–Southern Oscillation and the Atlantic Multidecadal Oscillation. Climate variations due to these large-scale patterns directly impact the U.S. Caribbean because the islands largely rely on surface waters and consistent annual rainfall to meet freshwater demands. The high percentage of coastal areas relative to the total island land area means that a large proportion of the region's people, infrastructure, and economic activity are vulnerable to sea level rise, more frequent intense rainfall events and associated coastal flooding, and saltwater intrusion. As on islands worldwide, there are strong socioeconomic and cultural ties to diminishing marine resources and services, as well as economic dependence on tourism and imported goods. 

From the vibrant colors and sounds of the island rainforest to the bustling streets of Old San Juan, this small island is packed with diverse natural and cultural resources. 
[Open the image link to view a larger version of this image and a Spanish translation of the image caption.]

The people of the U.S. Caribbean rely heavily on imported food and other goods and services, leaving them critically exposed to climate-related disruptions in transportation systems, as well as vulnerabilities associated with source geographies. Crop species key to regional economies and food security—such as coffee, plantains, and mangoes—have evolved in narrower climatic niches relative to temperate crops and are often detrimentally affected by relatively small shifts in temperature, humidity, and rainfall. The limited geographic and economic scale of Caribbean islands means that disruptions from extreme climate-related events, such as droughts and hurricanes, can devastate large portions of local economies and cause widespread damage to crops, water supplies, infrastructure, and other critical resources and services.

The diverse natural resources of the islands are sensitive and often extremely vulnerable to natural and man-made hazards and are likely to become more vulnerable as climate change continues. Among the vulnerabilities and threats to the coastal zones of the islands are saltwater intrusion, flooding, and the increased frequency or intensity of tropical storms. In Puerto Rico and the USVI, poor coastal and shoreline management practices have resulted in the replacement of natural systems such as mangrove wetlands with hardened structures, altering sediment transport patterns and increasing coastal erosion in many areas. In Puerto Rico, poor maintenance of stormwater management systems has resulted in sedimentation and water quality issues that affect natural resources. 

Observed Climate

The local climate is tropical marine (warm and humid conditions), primarily influenced by the ocean, with annual average coastal temperatures of about 80°F (26 °C). Temperatures are generally coolest in January and warmest in August. Precipitation across Puerto Rico varies seasonally, with wetter summers and relatively drier winters. Trade winds blow predominantly from the east and northeast. The sea state for this region varies seasonally and is dominated by energetic tropical storms in the fall and large winter swells from November to April.

Climate trends and projections for the future

• Average temperature in Puerto Rico has increased 1.5°F since 1950. Projections for end-of-century temperatures show increases as high as 9°F unless the accumulation of heat-trapping gasses is reduced.

This figure, featured in the Caribbean chapter of the Fourth National Climate Assessment, illustrates the long-term (1971–2016) average annual number of days exceeding 90°F in Puerto Rico. The trend indicates that on average, people are now experiencing an additional half day per year above 90°F on the island. 

• Climate models project significant drying in the U.S. Caribbean region by the middle of this century. Results estimate a decline of more than 10% in annual precipitation if global emissions of heat-trapping gasses continue increasing.
• Sea surface temperatures have warmed and ocean chemistry has changed, becoming more acidic as it absorbs carbon dioxide from the atmosphere.
• Sea level is rising, and the rate of rise is accelerating. 

Learn more

To learn more about the impacts of climate change and variability and building climate resilience in the U.S. Caribbean, visit these pages:

• Natural Systems
• Economy
• Climate and Health

This narrative is excerpted and adapted from the following reports: 

Bhardwaj, A., Misra, V., Mishra, A., Wootten, A., Boyles, R., Bowden, J.H., Terando, A.J., 2018. Downscaling future climate change projections over Puerto Rico using a non-hydrostatic atmospheric model. Climatic Change 147, 133–147. https://doi.org/10.1007/s10584-017-2130-x

Describing the Ocean Economies, “Tourism: A Driver for Economic Growth”, Oct. 2016. [Online]. Accessed December 28, 2021.

DRNA: Programa de Manejo de la Zona Costanera (2017). Estado de la Costa de Puerto Rico. Ernesto L. Díaz y Karla M. Hevia, editores.

Financial Oversight and Management Board for Puerto Rico, “Memorandum: Labor Reform as a Catalyst for Growth.” [Online]. Accessed December 28, 2021.

Government of Puerto Rico, “Transformation and Innovation in the Wave of Devastation: An Economic and Disaster Recovery Plan for Puerto Rico,” Aug. 2018. [Online] Accessed December 28, 2021.

National Oceanic and Atmospheric Association (NOAA) Office of Coastal Management (OCM) project, Describing the Ocean Economies of the U.S. Virgin Islands and Puerto Rico (Task Order EA133C-14-BA-0039/C-003).

NOAA National Centers for Environmental Information, State of the Climate: National Climate Report for Annual 2019, published online January 2020, retrieved on February 19, 2021 from https://www.ncdc.noaa.gov/sotc/national/201913.

Puerto Rico Climate Change Council (PRCCC), 2013: Puerto Rico State of the Climate 2010-2013: Assessing Puerto Rico’s Social-Ecological Vulnerabilities in a Changing Climate. Puerto Rico Coastal Zone Management Program, Department of Natural and Environmental Resources, NOAA Office of Ocean and Coastal Resource Management, San Juan, PR.

“Puerto Rico’s Climate and Average Temperatures.” https://welcome.topuertorico.org/reference/tempera.shtml (accessed Feb. 19, 2021).
 
Puerto Rico Planning Board. 2015. Gross National Product and Gross Domestic Product by Major Industrial Sector. Statistical Appendix of the Economic Report for the Governor and Legislative Assembly. Available: http://www.bgfpr.com/economy/statistical-appendix.html. 

Runkle, J., K. Kunkel, and L. Stevens, 2018: Puerto Rico and the U.S. Virgin Islands State Climate Summary. NOAA Technical Report NESDIS 149-PR, 4 pp.

The Financial Oversight and Management Board for Puerto Rico, “New Fiscal Plan for Puerto Rico: Restoring Growth and Prosperity,” Jun. 2019.