U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 040-99

April 1999

Puerto Rico

Hurricane Georges

At 7 p.m. on Monday, Sept. 21, 1998,

the eye of Hurricane Georges made

landfall near Yabucoa and Humacao

on the east coast of Puerto Rico (fig.

1). Hurricane Georges traversed the

island from east to west, lashing

furiously at urban and rural areas

indiscriminately with estimated

sustained winds of 115 miles per hour

and gusts of 150 miles per hour. The

storm had a minimum central pressure of 957 millibars and was classified as a Category 3 Hurricane on the

Saffir-Simpson Scale. By 1 a.m. the

next day, Hurricane Georges had left

the island severely damaged and

flooded. Hurricane Georges produced

heavy rains over Puerto Rico, especially in the central interior mountains. The U.S. Geological Survey

(USGS) rain gage network reported

totals that ranged from less than 4

inches to about 26 inches near the

center of the island (fig. 2).

On Sept. 22, most of the mountainous

interior and the northern and southeastern coasts experienced severe

floods. The worst flooding occurred

in the river basins of the Río Grande

de Añasco, Río Culebrinas, Río

Camuy, Río Grande de Arecibo, Río

de la Plata, Río Patillas, and Río

Maunabo. Floodwaters inundated

urban areas and communities, washing away and damaging homes,

businesses, vehicles, bridges, and

roads. Fortunately, there were no

deaths directly associated with the

passage of the hurricane over Puerto

Rico. Damage to the island infrastructure was enormous. The total damage

in Puerto Rico was estimated at 1.9

billion dollars. Many landslides

occurred on the slopes of the mountainous interior, causing several

towns to be isolated for several days.

The USGS collected peak stage and

discharge information from the

streamflow-gaging network throughout the island. High-water marks

were surveyed shortly after the event.

20

0 10 20 30 KILOMETERS

0 10 30 MILES

18°00 ́

18°30 ́

30 ́ 67°00 ́ 30 ́ 66°00 ́ 30 ́

San Juan 

ATLANTIC OCEAN 

CARIBBEAN SEA

EXPLANATION

Precipitation, in inches

Greater than 24 inches

20–24 inches

15–20 inches

10–15 inches

5–10 inches

Less than 5 inches

Figure 2. Precipitation totals from Hurricane Georges.

EXPLANATION

0

0

10

10

20 KILOMETERS 

20 MILES

Approximate path of the 

eye of Hurricane Georges

WEBB study area

18°00 ́

18°30 ́

67°00 ́ 30 ́ 66°00 ́ 30 ́

Atlantic Ocean 

Caribbean Sea 

Gulf of 

Mexico Puerto Rico

Mayagüez

Cabo Rojo 

Ponce

Jayuya

Florida

Yabucoa

Humacao

Fajardo

Vieques

Culebra

Arecibo San

Juan 

ATLANTIC OCEAN 

CARIBBEAN SEA 

Río 

Culebrinas 

Río Río Grande 

Camuy de Arecibo 

Río Grande

de Añasco 

Río Grande

de Loíza 

Río de 

la Plata 

Patillas Maunabo

Río Río 

Lago de 

 la Plata

Lago

 Loíza

Figure 1. Path of Hurricane Georges in relation to Puerto Rico and USGS

study sites.
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Real-Time Hazard Alert Network

The USGS maintains and operates a

real-time hazard alert network

throughout Puerto Rico in cooperation with local government agencies.

The network consists of 122 hydrologic data-collection sites equipped

with satellite telemetry instrumentation. It includes streamflow, lakestage, rainfall, and meteorological

stations. Data collected at these

stations are transmitted to a geostationary satellite, which in turn

transmits the information to a receiving station in San Juan. The received

data are interpreted by computer,

and the data are made available to

cooperating agencies. The stage and

streamflow data also are made

available on the World Wide Web

at http://pr.water.usgs.gov and

http://vi.water.usgs.gov. This is the

only real-time hazard alert network in

the Caribbean, and it has proved

useful to government agencies during

storms and floods. The USGS provided this important scientific information before, during, and after

Hurricane Georges.

Coral Mortality and Hurricanes

A 1998 study of the coral reef around

Culebra, a small island off the east

coast of Puerto Rico, revealed that the

rapid recovery observed following the

devastation of the reef by Hurricane

Hugo in Sept. 1989 had slowed (fig.

3). In 1991, observation by divers

showed hurricane damage to the reefs

to be extensive. The most obvious

effect of the storm was the almost

total destruction of the elkhorn coral,

a principal reef builder in the Caribbean; virtually all colonies larger than

1 meter were overturned and fragmented. Finger and staghorn corals

also were greatly affected. Large

quantities of these delicate branching

corals had been reduced to rubble,

forming steep slopes that buried other

corals. Despite extensive damage to

the reefs, abundant evidence of posthurricane recruitment and regrowth

was noted during 1991 and 1994.

Landslide Hazard Assessment

High-energy storms, such as Hurricane Georges, regularly bring intense

and prolonged rainfall to Puerto Rico.

These events have triggered hundreds

of landslides in the mountainous

areas of the island where hillslopes

are steep and mean annual rainfall is

high. Each year, landslides cause

extensive damage to property, and

they occasionally result in loss of life.

Population density in Puerto Rico is

high, and it is increasing. This

increase is accompanied by the use of

less desirable construction sites, and,

as a result, human populations are

becoming more vulnerable to landslide hazards. To address this problem, a map showing landslide susceptibility in Comerío was published in

1998 (fig. 4). The map was compiled

using a methodology developed by

the USGS in an earlier study in the

mountains of eastern Puerto Rico; the

method uses topographic, geologic,

and land-use information to categorize all hillslopes into zones of low,

moderate, or high landslide susceptibility.

Figure 3. In 1959, this large

Colpophyllia natans (a type of brain

coral) had a star coral attached at left

and a species of Diploria on the right.

In 1988, the star coral is missing (note

cavity in foreground), but the Diploria

at right remained (Hurricane Donna

impacted this area in Sept. 1960). In

1998, the brain coral is slightly

bleached, and the Diploria to the right

is even more bleached. The brain

coral is mostly dead, and it is infested

with algae and sea whips.

EXPLANATION

300

Landslide susceptibility

High

Moderate

Low

Debris-flow track

Topographic contour—Interval 50 

meters

Comerío

Río de la Plata

350

300

250

250

200

Figure 4. Excerpt from map showing

susceptibility to landslides in the

municipality of Comerío, Puerto Rico.
Puerto Rico

Tsunami and Seismic Hazards

Puerto Rico and the Virgin Islands

exist on microplates located along a

plate boundary between the Caribbean plate and the North American

plate. The North American plate

moves west relative to the Caribbean

plate, a motion that grinds the plates

together and results in earthquakes,

massive seafloor landslides, and

tsunamis. Recorded tsunamis caused

about 100 deaths in 1946 and 91

deaths in 1918 in the region. The

USGS has studied earthquake locations beneath the islands, and has

concluded that the main plates (the

Caribbean plate to the south and the

North American plate to the north)

are bent down beneath the microplates that carry the islands, and they

may even be in contact at great

depths (perhaps 100 kilometers

beneath the surface). Stresses at this

contact may partly explain the

presence of the Puerto Rico trench,

the deepest spot in the Atlantic, to the

north of Puerto Rico. The downwarping of the trench results in tilting

of the limestone platform that surrounds Puerto Rico, and it probably

causes the detachment of great slabs

of rock that have slid down into the

Puerto Rico trench. If the slides occur

abruptly, perhaps triggered by earthquakes, these massive movements of

the ocean floor may generate tsunamis. Tsunamis also can be generated

by abrupt offsets of the seafloor

directly caused by earthquakes.

Puerto Rican Parrot

The USGS is participating in an

interagency effort to reintroduce

captive-bred Puerto Rican parrots

(fig. 5) into native habitat on Puerto

Rico. The parrot once ranged widely

across the island, but now it is one of

the most endangered bird species in

the West Indies; only a few dozen

parrots remain in the wild. The

parrots face a variety of problems that

Figure 5. Puerto Rican Parrot.

affect their ability to survive and

reproduce, including predators (redtailed hawks and rats) and botflies, a

parasite that kills nestlings. A successful captive breeding program has

created the potential for a second wild

population to be introduced in northcentral Puerto Rico.

Dengue Fever

Dengue fever, a viral disease transmitted by the mosquito Aedes aegypti

(fig. 6), can spread rapidly in explosive epidemics. More than a million

people per year worldwide are

afflicted by dengue, the most significant mosquito-borne disease affecting

humans. The incidence of dengue has

risen, and dengue epidemics have

occurred with increasing frequency in

the Caribbean. In Puerto Rico,

dengue is a seasonal disease estimated to be responsible for more than

1,000 hospitalizations annually.

Dengue transmission is influenced by

the behavior of Aedes aegypti, the

movement and distribution of humans, and virus development within

the mosquito. The role of each of

these factors is poorly understood, in

part, because of the absence of

studies on the spatial-temporal

patterns of dengue cases. In an effort

to add a geographic component to the

existing Puerto Rico dengue surveillance program, a project funded

cooperatively by the USGS, the

Centers for Disease Control and

Prevention (CDC), and the Puerto

Rico Department of Health was

begun in 1994. The project employed

a geographic information system to

study the spatial and temporal distribution of dengue cases reported to the

CDC’s dengue surveillance system.

Significant dengue case clustering

was identified at very short distances

(most likely within households) over

short time periods (3 days or less).

This was probably a result of multiple

feeding behavior on the part of the

Aedes aegypti mosquito.

Water Use: 1980–1995

The population of Puerto Rico has

increased 15 percent from 1980 to

1995 (fig. 7); however, the total

freshwater per capita withdrawals

decreased. Total freshwater per capita

withdrawals in 1995 were 154 gallons

per day per person compared to 176

gallons per day per person in 1985—

Figure 6. Aedes aegypti mosquito.

WITHDRAWALS, IN MILLION 

POPULATION IN MILLIONS

GALLONS PER DAY

0

100

200

300

400

500

1980 1985 1990 1995

3

3.5

4

Population

Ground water 

Surface water

Figure 7. Population and water-use

trends in Puerto Rico.
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USGS office locations USGS State Representative

651 Federal Drive

Suite 400-15

Guaynabo, PR 00965

(787) 749-4346

FAX (787) 749-4462

USGS Home Page:

http://www.usgs.gov

Reports and products:

1-888-ASK-USGS

that decrease in water use may be

attributed to the implementation of

water conservation programs primarily in industry and agriculture.

Puerto Rico enjoys a tropical maritime climate with an average of 72

inches of rain annually. Droughts

occur, but they are infrequent. The

most recent drought was during

1993–94, and it affected the San Juan

area. Water reserves at the Loíza and

La Plata reservoirs, which provide

potable water to more than 750,000

people in the San Juan area, were

reduced to below their critical levels.

During the drought, intensive rationing was implemented. This drought

increased the demand for groundwater supplies, and it adversely

affected the economy of Puerto Rico.

Long-Term Study of Water, Energy,

and Biogeochemical Budgets

The USGS Water, Energy, and

Biogeochemical Budget Program

(WEBB) began in 1991 at five

locations in the United States,

including one in Puerto Rico (fig. 1).

The Puerto Rico research site consists

of the U.S. Forest Service-administered Luquillo Experimental Forest

and the Río Grande de Loíza drainage

basin, an agriculturally developed

watershed. This combined region

serves as a terrestrial laboratory for

the study of issues related to the

global loss of tropical forest and the

associated changes in land-use

practices. The research focuses on

geomorphic and biogeochemical

processes that control the movement

and transformation of water, energy,

bedrock weathering products, and

nutrients. The study examines erosion

processes, soil development, nutrient

cycling, and hillslope and fluvial

transport of sediment and dissolved

chemicals. One important finding to

date is that intense agricultural

practices of the 19th and early 20th

century have resulted in high suspended sediment yields many decades

after farming ceased. Sediment was

eroded from the hillslopes while they

were being farmed, and it was then

deposited at the base of the hillslopes.

Since then, storm flows have episodically moved the sediment from the

base of the hillslopes downstream

where it is deposited in reservoirs or

coastal estuaries and coastal waters

where coral reefs are located. The

sediment and associated contaminants

negatively affect the water quality

and organisms in these areas. Water

budgets have also been developed to

show how much precipitation, stream

runoff, ground-water loss, and

evapotranspiration have occurred in

each watershed during the 1990’s

(fig. 8). The water budgets are

strongly controlled by elevation and

location with respect to prevailing

(trade) winds. More information

about this program can be found at

http://pr.water.usgs.gov/public/webb.

0

100

200

300

400

500

Icacos Mameyes Canóvanas

CENTIMETERS PER YEAR

Cayaguás

Inputs

Outputs

Evapotranspiration

Figure 8. Average water budgets of

four watersheds in eastern Puerto

Rico, water years 1991 to 1997. Inputs

include rainfall, cloud drip, and

infiltration from septic tanks. Outputs

include runoff, ground-water flow,

and extraction for public consumption. Evapotranspiration is estimated

as the difference between inputs and

outputs.

Cayey

San Juan

Guaynabo

The USGS has 78

employees in Puerto Rico