Federal Coordinating Lead Author:
William A. Gould, USDA Forest Service International Institute of Tropical Forestry
Chapter Lead:
Ernesto L. Diaz, Department of Natural and Environmental Resources, Coastal Zone Management Program
Chapter Authors:
Nora L. Álvarez-Berríos, USDA Forest Service International Institute of Tropical Forestry
Felix Aponte-González, Aponte, Aponte & Asociados
Wayne Archibald, Archibald Energy Group
Jared Heath Bowden, Department of Applied Ecology, North Carolina State University
Lisamarie Carrubba, NOAA Fisheries, Office of Protected Resources
Wanda Crespo, Estudios Técnicos
Stephen Joshua Fain, USDA Forest Service International Institute of Tropical Forestry
Grizelle González, USDA Forest Service International Institute of Tropical Forestry
Annmarie Goulbourne, Environmental Solutions Limited
Eric Harmsen, Department of Agricultural and Biosystems Engineering, University of Puerto Rico
Azad Henareh Khalyani, Natural Resource Ecology Laboratory, Colorado State University
Eva Holupchinski, USDA Forest Service International Institute of Tropical Forestry
James P. Kossin, National Oceanic and Atmospheric Administration
Amanda J. Leinberger, Center for Climate Adaptation Science and Solutions, University of Arizona
Vanessa I. Marrero-Santiago, Department of Natural and Environmental Resources, Coastal Zone Management Program
Odalys Martínez-Sánchez, NOAA National Weather Service
Kathleen McGinley, USDA Forest Service International Institute of Tropical Forestry
Melissa Meléndez Oyola, University of New Hampshire
Pablo Méndez-Lázaro, University of Puerto Rico
Julio Morrell, University of Puerto Rico
Isabel K. Parés-Ramos, USDA Forest Service International Institute of Tropical Forestry
Roger Pulwarty, National Oceanic and Atmospheric Administration
William V. Sweet, NOAA National Ocean Service
Adam Terando, U.S. Geological Survey, Southeast Climate Adaptation Science Center
Sigfredo Torres-González, U.S. Geological Survey (Retired)
Review Editor:
Jess K. Zimmerman, University of Puerto Rico
Technical Contributors:
Mariano Argüelles, Puerto Rico Department of Agriculture
Gabriela Bernal-Vega, University of Puerto Rico
Roberto Moyano, Estudios Técnicos Inc.
Pedro Nieves, USVI Coastal Zone Management
Aurelio Mercado-Irizarry, University of Puerto Rico
Dominique Davíd-Chavez, Colorado State University
Rey Rodríguez, Puerto Rico Department of Agriculture
USGCRP Coordinators:
Allyza Lustig, Program Coordinator
Apurva Dave, International Coordinator and Senior Analyst
Christopher W. Avery, Senior Manager

U.S. Caribbean

Puerto Rico and the U.S. Virgin Islands (USVI) are rich in biodiversity, cultural heritage, and natural resources. More than 3.5 million inhabitants depend on the region’s natural resources and environmental services for their well-being, livelihoods, local economies, and cultural identities. 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 ecosystems services.


Figure 20.1: U.S. Caribbean Region

Figure 20.1: The U.S. Caribbean includes the Commonwealth of Puerto Rico and the territory of the U.S. Virgin Islands. The region includes seven inhabited islands and nearly 800 smaller islands and cays.


The U.S. Caribbean (Figure 20.1) includes the inhabited commonwealth islands of Puerto Rico, Vieques, and Culebra (with a combined population of 3.4 million), along with the inhabited territorial islands of St. Croix, St. Thomas, St. John, and Water Island (with a combined population of 104,000). In addition to the principal islands, the U.S. Caribbean includes over 800 smaller islands and cays, diverse cultural and historical resources, and a rich matrix of marine and terrestrial ecosystems. The region’s physical geography includes nearshore and open ocean marine areas; coastal wetlands, hills, and plains; limestone (or karst) hills; and interior mountains. Average rainfall amounts vary widely across the region, and social and ecological systems are diverse. Puerto Rico and the USVI share many vulnerabilities with coastal states and the Pacific Islands but lack much of the capacity available to 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, similar to the Pacific Islands (Ch. 27: Hawai‘i & Pacific Islands). Additionally, differences in the natural and social systems, and in information availability for Puerto Rico and the USVI, affect the degree of vulnerability to climate change and extreme climate events. This is reflected in different needs, priorities, and approaches to reducing vulnerability between Puerto Rico and the USVI. 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 atmospheric greenhouse gas concentrations increase. Having evolved with these 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 (Figure 20.2).18,19

The vulnerability of the U.S. Caribbean region 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.20 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.1,13,14,21 High levels of exposure and sensitivity to risk in the region are compounded by a low level of adaptive capacity, due in part to the high costs of mitigation and adaptation measures relative to the region’s gross domestic product, particularly when compared to continental U.S. coastal areas.1

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.22 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.13,23,24 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.1,25


Figure 20.2: Climate Indicators and Impacts

Figure 20.2: (top) Key indicators for monitoring climate variability and change in the U.S. Caribbean include sea level rise, ocean temperature and acidity, air temperature, rainfall patterns, frequency of extreme events, and changes in wildlife habitats. (bottom) Changes in these climate indicators result in environmental and social impacts to natural ecosystems, infrastructure, and society, including degradation of coral and marine habitats, increased coastal flooding and erosion, decrease in agricultural productivity, water supply shortages, negative effects on communities’ livelihoods and on human health, as well as economic challenges and decreased tourism appeal. Source: Puerto Rico Department of Natural and Environmental Resources.


Observed and Projected Climate Change

The Climate Science Special Report (CSSR)26 provides an in-depth assessment of observed and projected climate change in the continental United States. Because this level of assessment was not available for the U.S. Caribbean region, this section provides a brief overview of observed trends and future projections of five climate variables that are relevant to assessing climate change risk in the region: temperature, precipitation, sea surface temperature, ocean acidification, and sea level rise.


Figure 20.3: Observed and Projected Temperature Change for Puerto Rico

Figure 20.3: Observed and projected temperature changes are shown as compared to the 1951–1980 average. Observed data are for 1950–2017, and the range of model simulations for the historical period is for 1950–2005. The range of projected temperature changes from global climate models is shown for 2006–2100 under a lower (RCP4.5) and a higher (RCP8.5) scenario (see the Scenario Products section of App. 3). Projections from two regional climate models are shown for 2036–2065, and they align with those from global models for the same period.29,30 Sources: NOAA NCEI, CICS-NC, and USGS.


Temperature. Annual average temperatures in the U.S. Caribbean have fluctuated over the last century. However, since 1950, temperatures have increased by about 1.5°F in Puerto Rico.27 Projected increases under both a lower and higher scenario (RCP4.5 and RCP8.5) are expected in both average and extreme temperatures, which will lead to more days per year over 95°F and more nights per year over 85°F.28 Global climate models project about a 1.5°F to 4°F increase in average temperatures for the U.S. Caribbean by 2050. End-of-century estimates show temperature increases as high as about 9°F under a higher scenario (RCP8.5; Figure 20.3).7


Figure 20.4: Projected Precipitation Change for Puerto Rico

Figure 20.4: This figure shows the projected percent change in annual precipitation over the U.S. Caribbean region for the period 2040–2060 compared to 1985–2005 based on the results of two regional climate model simulations.29,30 These simulations downscale two global models for the higher scenario (RCP8.5)26 and show that within-island changes are projected to exceed a 10% reduction in annual rainfall. Uncertainty remains as to the location of the largest reductions within the islands. Projections of precipitation change for the U.S. Virgin Islands are particularly uncertain because of model limitations related to resolving these smaller islands. Source: Bowden et al. 2018.30


Precipitation. Globally, subtropical regions are expected to become drier in the future, especially in regions such as the U.S. Caribbean where oceans have the largest influence on local precipitation patterns.31 Climate model results consistently project significant drying in the U.S. Caribbean region by the middle of this century, specifically, a decline of more than 10% in annual precipitation under the higher scenario (RCP8.5; Figure 20.4).7,28,30,32 The magnitude of this projected drying, particularly for climate scenarios with the highest amounts of warming, is in general lower in the most recently developed climate models.28 The region is likely to experience more intense rainfall events associated with tropical cyclones;33 however, uncertainty remains regarding various aspects of extreme rainfall within the region, such as the frequency and duration of extreme rainfall events associated with tropical cyclones.28,34 For instance, one study34 finds less frequent extreme rainfall events on average in the future at sub-daily and daily timescales, while another28 finds more frequent extreme rainfall events that exceed 3 inches of rain in a day, as well as more intense rainfall associated with tropical cyclones.28,33


Figure 20.5: Ocean Chemistry and Temperature

Figure 20.5: This figure represents an annual time series from 1993 to 2016 of atmospheric carbon dioxide (CO2; black line) , sea surface temperature (red line), and seawater pH (blue line) for the Caribbean region. The Caribbean ocean is subject to changes in surface pH and temperature due to the increase in atmospheric CO2 concentrations. The oceans have the capacity to not only absorb heat from the air (leading to ocean warming) but also to absorb some of the CO2 in the atmosphere, causing more acidic (lower pH) oceans. Continued ocean acidification and warming have potentially detrimental consequences for marine life and dependent coastal communities in the Caribbean islands. Source: University of Puerto Rico.


Sea surface temperature and ocean acidification. Globally, surface ocean waters have warmed by about 1.3°F per century between 1900 and 2016.35 Over the period 1955–2016, the waters of the northeast Caribbean increased in temperature at a rate of 0.23°F per decade,36 and over the last two decades, the sea surface warming rate has reached 0.43°F per decade (Figure 20.5).

Sea level rise. Since the middle of 20th century, relative sea levels have risen by about 0.08 inches (2 mm) per year on average along the coasts of Puerto Rico and the USVI.37,38 However, rates have been slowly accelerating since the early 2000s and show noticeable acceleration (by a factor of about 3) starting in about 2010–2011. This recent accelerating trend is in agreement with what has been observed along the southeastern U.S. seaboard, and rates of global and regional relative sea level rise are projected to continue to increase substantially this century, largely dependent on the amount of future greenhouse gas emissions. Under the Intermediate-Low, Intermediate, and Extreme scenarios, relative sea levels are projected to rise by about 0.8 feet, 1.2 feet, or 2.8 feet (24 cm, 37 cm, or 84 cm), respectively, by 2050 across the region compared to levels in 2000 and by about 1.6 feet, 3.6 feet, or 10.2 feet (0.5 m, 1.1 m, or 3.1 m), respectively, by 2100 (Figure 20.6).38 Additionally, the region may experience more than the global average increase under the higher scenarios in response to changes in the Earth’s gravitational field and rotation due to melting of land ice, ocean circulation, and vertical land motion.


Figure 20.6: Observed and Projected Sea Level Rise

Figure 20.6: (top) Observed sea level rise trends in Puerto Rico and the U.S. Virgin Islands reflect an increase in sea level of about 0.08 inches (2.0 mm) per year for the period 1962–2017 for Puerto Rico and for 1975–2017 for the U.S. Virgin Islands. The bottom panels show a closer look at more recent trends from 2000 to 2017 that measure a rise in sea level of about 0.24 inches (6.0 mm) per year. Projections of sea level rise are shown under three different scenarios of Intermediate-Low (1–2 feet), Intermediate (3–4 feet), and Extreme (9–11 feet) sea level rise. The scenarios depict the range of future sea level rise based on factors such as global greenhouse gas emissions and the loss of glaciers and ice sheets. Sources: NOAA NCEI and CICS-NC.


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