finding 20.5 : key-message-20-5

Extreme events pose significant risks to life, property, and economy in the Caribbean, and some extreme events, such as flooding and droughts, are projected to increase in frequency and intensity (flooding as likely as not, medium confidence; droughts very likely, medium confidence). Increasing hurricane intensity and associated rainfall rates (likely, medium confidence) will likely affect human health and well-being, economic development, conservation, and agricultural productivity. Increased resilience will depend on collaboration and integrated planning, preparation, and responses across the region (high confidence).



This finding is from chapter 20 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

The majority of our Key Messages were developed over the course of two separate author meetings. The first occurred March 9–10, 2017, and the second on May 3, 2017. Both meetings were held in San Juan, Puerto Rico; however, people were also able to join remotely from Washington, DC, Raleigh, North Carolina, and the U.S. Virgin Islands (USVI). In addition, the author team held weekly conference calls and organized separate Key Message calls and meetings to review and draft information that was integral to our chapter. To develop the Key Messages, the team also deliberated with outside experts who are acknowledged as our technical contributors.


Description of evidence base:

On both Puerto Rico and the USVI, disaster events have caused billions of dollars in property and crop damages.cdbb39c1-4de9-4067-8ebc-24de32b50b57 Over the years, disaster-induced casualties have declined in both territories. Tropical cyclones, particularly hurricanes, continue to generate the most severe economic damage across the U.S. Caribbean. Floods and droughts are challenging to manage for both territories, and these challenges may be exacerbated by climate change induced shifts in precipitation regimes.

Climate modeling for tropical cyclone activity in the Atlantic Basin, including the Caribbean region, points toward an increase in the frequency of more intense hurricanes.349482df-4a77-4802-8b39-14d5e63b946f An increase in days with more than 3 inches of rain per 24-hour period is projected for Puerto Rico, based on statistically downscaled CMIP3 climate models.56d77153-c8fc-4fcf-a7f0-fa0e843936f1 Changes in precipitation patterns are expected for Puerto Rico in the periods 2030–2050 and 2100, pointing toward an overall decrease in mean precipitation for different climate change scenarios.650b2907-85b1-4b76-a339-a9ec1703c5bd,56d77153-c8fc-4fcf-a7f0-fa0e843936f1,66a435ae-179c-49f4-981b-248d647b9579,744497bd-974c-497e-bf74-34ff514c0f83

While continental droughts typically affect vast regions, droughts affecting Puerto Rico and the USVI tend to vary significantly in extent and severity over smaller distances.edd9a004-f859-41ae-9f93-80201c4ffd65 Statistically downscaled climate projections for Puerto Rico suggest an increase of drought intensity (measured as the total annual dry days) and extremes (measured as the annual maximum number of consecutive dry days) due to an increase in mean and extreme temperatures and a decrease in precipitation.650b2907-85b1-4b76-a339-a9ec1703c5bd

An increase in mean atmospheric temperature has been observed across the U.S. Caribbean islands, particularly on Puerto Rico. An analysis of the observed temperatures across several NOAA weather stations in Puerto Rico showed rising temperature trends between 1970 and 2016.e8d32931-3301-45c8-bfe7-b8e8b9fff6b6 Following the principles established by the international Expert Team on Climate Change Detection and Indices,e6ecbe14-fe1b-46f8-bad5-bde9e4cc658a temperature extremes and trends were identified, indicating significant increases in rising annual temperatures and an increase in extreme heat episodes.

New information and remaining uncertainties:

There are still uncertainties as to how these projected changes in tropical Atlantic cyclone activity will affect the frequency distribution of extreme precipitation events. While an increase in days with more than 3 inches of rain per 24-hour period has been projected based on statistically downscaled CMIP3 models,56d77153-c8fc-4fcf-a7f0-fa0e843936f1 more recent generations of GCMs do not show this increase in extreme rainfall events, and this adds uncertainty. Results from two dynamically downscaled climate models using the most recent generation of GCMs for the region do not show increases in the frequency of extreme events.744497bd-974c-497e-bf74-34ff514c0f83

At present, data pertaining to the costs and effects that are associated with extreme events and disasters are very limited and not readily accessible for government officials, disaster risk managers, or the general public. In the future, more accessible data could facilitate opportunities for more thorough analyses on the economic costs of extreme events for the U.S. Caribbean.

Assessment of confidence based on evidence:

There is high confidence that increasing frequency of extreme events threatens life, property, and economy in the region, given that the U.S. Caribbean’s vulnerable populations and fragile economies are continually exposed to climate extremes. There is medium confidence that the frequency and intensity of the most extreme hurricanes and droughts will likely increase. There is high confidence that extreme events will likely continue to affect human health and well-being, economic development and tourism, conservation, agriculture, and danger from flooding. There is high confidence that future recovery and cultural continuity will depend on significant and integrated resilience planning across the region, focusing on collaborative actions among stakeholders.

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