Puerto Rico - Environment

Tropical climate is very unpredictable and it can start raining out of the blue. Puerto Rico offers a rich tapestry of environments in which to conduct field studies in tropical ecology. It has a mountain range oriented east-west with peaks as high as 1000 meters (4,000 feet). Its boundary on the north is the Atlantic Ocean and to the south, the Caribbean Sea. The island is bathed by the westerly trade winds, which interact with the sea and mountains to produce an array of rainfall patterns and orographically induced habitat variation. Some areas in the mountains receive more than 5000 millimeters (200 inches) of rain annually. Other areas on the Caribbean rain shadow side receive as little as 254 millimeters (10 inches) in some years.

In addition, the rainfall produces considerable runoff that results in many rivers on the island in all directions. The south side has fewer perennial rivers and is a lower energy coast line, thus affording greater stability to marine ecosystems such as coral reefs, mangrove swamps, and submerged seagrass beds.

The island is in the hurricane belt of the western Atlantic and Caribbean. Most hurricanes form as tropical lows off the coast of Africa from June through October and intensify as they proceed west over the warm waters of the Atlantic. Hurricanes are Puerto Rico’s number one weather problem because of the catastrophic high winds and waves, large volumes of rain, and the enormous structural change they can produce on natural ecosystems, and on human populations and their infrastructure. Most hurricanes are peripheral and produce minor effects, but those termed killer hurricanes owing to their intensity and direct hits, have the potential to produce enormous damage and hardship. Typically, 6 to 10 hurricanes develop yearly in the western North Atlantic region. Hurricanes have impacted Puerto Rico recently, with Hortense, Hugo, and George classed as major hurricanes.

Because of its geographic position, half the year Puerto Rico is also exposed to major tropical storms. Hurricanes are one of the main ecological disturbances in Puerto Rico and all adjacent areas of the Caribbean, and have the potential of producing enormous instantaneous and long-term change in all ecosystems, terrestrial and marine.

Puerto Rico is in that large area north and south of the equator called the tropics (25° N and S). Its maritime climate is very pleasant because it is bathed by warm sea breezes throughout the year. This prevents major fluctuations in temperature. Rainfall is distributed throughout the year, with May through November considered the rainy period. January to March is a bit dryer, but may have cold fronts coming in from the temperate zone to the north that can produce 1 to 2 days of rain.

Extremes in temperature are rare, with high temperatures rarely going into the mid 30s °C (90 °F) except on the south coast and lows rarely below 25 °C (60 °F) in the mountains. Smallest daily temperature fluctuations occur in the coastal plain 5 to 8 °C (10 to 15 °F), whereas the mountains experience the largest daily fluctuations 8 to 12 °C (15 to 20 °F). There is not much variation seasonally like there is in the temperate zone, in fact there is greater night to day temperature variation than there is seasonally. However, there is considerable variation in temperature and precipitation resulting from variable topography and prevailing winds. The east-west mountain chain intercepts the easterly trade winds; thus it provides the north side with an abundance of rain. The Cordillera Central and Luquillo ranges cause the warm moisture-laden air masses to cool and lose much of their moisture as they pass over the north and eastern sides. As they pass over the mountains, the amount of rain decreases resulting in the south coast being much dryer.

Areas in the Luquillo Rain Forest often receive more than 5000 millimeters (200 inches) of rain, whereas areas in the Guánica Forest 42 kilometers (50 miles) away may only receive 900 millimeters (36 inches). The capital city of San Juan annually receives 1700 millimeters (68 inches) of rain on the north coast, whereas the second largest city, Ponce on the south coast, receives only 950 millimeters (38 inches). Some areas on the south coast may receive only 254 millimeters (10 inches) in dry years. The island’s average rainfall is 1800 millimeters (71 inches) per year.

The mountainous topography produces temperature variation. In general, for every 300-meter (1,000-foot) increase in altitude, temperature decreases 2 to 3 °C (3 to 4 °F). On average, San Juan’s coastal temperature will be 4 °C (7 °F) warmer than a town in the mountains such as Barranquitas. Many mountain communities experience almost idyllic climate, with temperature regimes that require neither air conditioning nor heating. People in the warmer, more humid coastal areas may use air conditioning throughout the year. Puerto Rico does not experience freezing temperatures, even in the highest mountains where temperatures rarely fall below 18 °C (65 °F). Much of the island experiences high humidity year round.

Many streams are formed as a result of the mountainous terrain. There are hundreds of mapped streams on the island, 50 of these are classed as rivers. Most rivers on the north side are larger in volume and length. Six major rivers originate in the Luquillo chain. Most of the rivers are dammed and used for regional or community water supplies, irrigation, and power production. The majority of the reservoirs have problems with sedimentation, water quality, and introduced exotic aquatic plants such as Eichornia crassipes (Mart.) Solms (water hyacinth) and Pistia stratiotes L. (water lettuce).

Today, forests cover approximately 40 percent of Puerto Rico. At one point, more than 90 percent of the forests of the island had been cleared, and those forested areas that remained were heavily disturbed. Since the 1960s, forest cover has been steadily increasing owing to industrialization and urbanization. Many formerly cleared areas that were on steep slopes or that became unproductive owing to poor agricultural practices are undergoing natural reforestation. The island is greener today than at any time in the 20th century.

Today, large expanses of agricultural lands are “returning to nature” as much of the sugar plantation land is being abandoned, as sugar is no longer the dominant crop that it was in the 18th, 19th, and first half of the 20th centuries. Consequently, Puerto Rico is an interesting case study in that it is an island undergoing significant natural reforestation. Many former agricultural sites will not return to forest as a result of rapid urban development, growth of tourism centers, golf courses, light industry, and transportation corridors for the rapidly increasing use of private automobiles. Human activity has also reduced and, in some cases, endangered many types of ecosystems, for example, the loss of coral reefs on the north coast, magnificent lowland forests of the alluvial coastal plains, coastal dune communities, and the elfin forests on the mountain tops, and the damming of numerous rivers.

Human activity in Puerto Rico is changing Puerto Rico’s complex landscape, but instead of being largely restricted to agricultural simplification of the landscape (for which there is an opportunity of recovery), much more destructive and permanent changes are occurring on the island. These include loss of large areas to urbanization; serious water pollution associated with improper disposal of sewage, including hazardous and other solid wastes (industrial and municipal); overpumping of critically important ground-water supplies; and the destruction of large numbers of limestone hills, sandy beaches, mangroves, freshwater swamps, and other wetlands. Development in Puerto Rico is growing at a rate that is surpassing regional carrying capacity in terms of public water supply in many areas, and at the expense of species and habitats. Puerto Rico is at a critical crossroads in its environmental history.

Climate Change

The U.S. tropical islands include Puerto Rico and the U.S. Virgin Islands in the Caribbean, and Hawai’i, Guam, the Northern Mariana Islands, and American Samoa in the Pacific. Many islands are especially vulnerable to the risks of climate change because of their small size, low elevation, remote geographical location, and concentration of infrastructure along coastlines. Islands are also home to unique ecosystems, including coral reefs, mangrove forests, and diverse populations of native species found nowhere else in the world. Island ecosystems are already stressed from human development and pollution, making them particularly sensitive to additional stresses from climate change.

Puerto Rico’s climate is changing. The Commonwealth has warmed by more than one degree (F) since the mid- 20th century, and the surrounding waters have warmed by nearly two degrees since 1901. The sea is rising about an inch every 15 years, and heavy rainstorms are becoming more severe. In the coming decades, rising temperatures are likely to increase storm damages, significantly harm coral reefs, and increase the frequency of unpleasantly hot days.

Cities, roads, and ports in Puerto Rico are vulnerable to the impacts of both winds and water during storms. Greater wind speeds and the resulting damages can make insurance for wind damage more expensive or difficult to obtain. Coastal homes and infrastructure are likely to flood more often as sea level rises because storm surges will become higher as well. As a result, rising sea level is likely to increase flood insurance premiums for people living along the coast.

Islands are experiencing rising air temperatures and sea levels, and warmer, more acidic coastal waters. Temperatures are expected to increase into the future, but will vary in the extent of warming that occurs based on location, elevation, and changes in ocean conditions. In the Caribbean, Puerto Rico is projected to warm by 2°F to 5°F by the end of this century. In Puerto Rico, an increasing amount of rain has been falling in the form of heavy downpours in recent history. The impacts of sea level rise are already being felt. In Rincón, Puerto Rico, sea level rise is currently eroding the coastline at a rate of about three feet per year.

Climate projections indicate Puerto Rico may be warmer and drier, likely impacting one of the Island's most iconic crops. This could result in less-favorable growing conditions in the coming decades for coffee. A May 2017 study by the USDA Caribbean Climate Hub shows that if greenhouse gas emissions and temperatures continue to increase, we may see a reduction in lands with highly-suitable conditions for coffee. Climate adaptation practices and research can help growers respond to new conditions and keep Puerto Rican coffee growing and flowing.

“This study is part of the USDA’s effort to develop and deliver information to help reduce the risks of climate variability and change”, said Dr. William Gould, Director of the Caribbean Hub based at the USFS International Institute of Tropical Forestry. The study, published in the journal Climatic Change, is the first to use fine-resolution climate projections for Puerto Rico to model the effects of warming temperatures and changing rainfall patterns on coffee growing conditions.

Coffea arabica (Arabica) accounts for the majority of production in Puerto Rico and worldwide. High temperatures and low precipitation can result in diminished coffee quality and yields, plus increased exposure and sensitivity to insects and diseases. “High greenhouse gas emission scenarios project temperature increases that, without adaptation, will make growing traditional varieties of Arabica challenging”, explained Stephen Fain, lead author of the study. “Our findings reveal differences in the potential effects of high and low CO2 emissions on coffee.”

Projections indicate that under high greenhouse gas emission scenarios Puerto Rico's mean annual temperatures will exceed parameters suitable for Arabica by mid-century. "Under low emission scenarios we will continue to have areas suitable for growing Arabica using current practices, but under the high emissions trajectory that seems increasingly unlikely”, added Fain. Coffee farmers and researchers around the world are joining efforts to find solutions to climate change challenges. Selective breeding has allowed the development of hybrid Arabica/Robusta varieties more resistant to coffee rust and higher temperatures. Growers are experimenting with techniques for conserving soil moisture, like increasing tree and shade cover, terracing steep farmlands, and employing drip irrigation.