Climate and Meteorology of the Galápagos Islands

by Chris Ader
July 6, 2000

Contents:

Introduction
The Influence on Oceanography on Climate
The Seasons
The Impact of El Niño on the Islands
Ice Ages in the Galápagos
Climate Statistics
Additional Reading
Introduction

"Considering that these islands are placed directly under the equator, the climate is far from being excessively hot; this seems chiefly cause by the singularly low temperature of the surrounding water, brought here by the great southern Polar current. Except during one short season, very little rain falls, and even then it is irregular; but the clouds generally hang low."
-Charles Darwin, The Voyage of the Beagle , 1845

While, like Darwin observed, the climate of the islands is hardly the tropical climate you would find in the Caribbean or South Pacific, the islands are not cold either, as average daytime temperatures in the lowlands usually reach at least 30°C (85°F). The average water temperature, however, is less than the 30°C needed to sustain the coral that surrounds many tropical islands. The islands have a varying climate marked by a scarcity of rain. The coastal areas are quite arid, covered with plants that have adapted to desert-like conditions, but lush vegetation grows in the highlands of the larger islands.

The Influence on Oceanography on Climate

The weather of the Galápagos Islands is influenced by three main ocean currents and, to a lesser extent, by four other ocean currents. Of the three major currents influencing the islands (Click here for map of currents), the Humboldt or Peru Current brings cold, nutrient-rich waters from Antarctica and Chile, the warm Panama Current is fed by the Northern Equatorial Countercurrent and provides the environmental environment for the development of tropical marine ecosystems, and Cromwell or Equatorial Undercurrent upon meeting the Galápagos platform upwells, especially off the coast of Fernandina and west Isabela, bringing deep waters, both cold and nutrient-rich, to the surface. Since the Galápagos islands are located at the intersection of these ocean currents the weather can change very quickly as s result of any change in the currents, and thus forecasting the weather in the islands is extremely difficult. The cold Humboldt and Cromwell currents cool the Galápagos Islands, and keep them from being the tropical islands one would expect to find at the equator.

The Seasons

There are two primary seasons in the Galápagos Islands, the wet season and the garúa, or dry season. The seasons are affected by the differences in the ocean currents, which are in turn effected by the differences in the trade winds. The seasonal difference in the islands is characterized more by a difference in precipitation and cloud cover than a difference in temperature, as the islands remain mild year-round.

The wet season, or hot season, lasts from December to May, when the Northeast Trade winds blow and the hot Panama Current prevails. During the wet season, there is usually plenty of sunshine and blue skies, the temperature of the islands increases, rainfall is abundant, and the average sea temperature in Academy Bay and the air temperature average 25°C (77°F). Even the abundant rainfall of the wet season comes in brief periods however, and it quickly drains through the porous volcanic soils. The water's surface is heated, and when this warmer water touches the cold currents, convection occurs and causes increased precipitation. The clouds are also lower, less frequent, and cumulus clouds are much more common during the wet season.

The garúa season, or dry season, lasts from June to November, when the Southeast Trade winds are stronger, and as a result the Humboldt Current and Cromwell Undercurrent predominate. These currents bring with them cooler air, which creates an inversion layer which upsets the usual weather pattern associated with the tropics. The moisture that evaporates from the ocean is clustered in this inversion layer (300 to 600m above sea level) and thus only the higher parts of the islands, which are in this layer, receive rain, and as a result, the palo santo forests of the lowlands are leafless. Even within the highlands, the southern and eastern slopes receive more rain than the northern slopes. As a result of the dominant currents, the air and the ocean are both cooler than during the wet season, as the sea temperature in Academy Bay and the air temperature average 22°C (72°F). During the garúa season, a fine drizzle often falls, especially in the highlands, giving the name to the season, as garúa is the Spanish word for mist. The sunshine is also less intense than during the wet season, and cloudier skies are the norm. The highlands are almost always cloud covered during the garúa season. Ironically, the highlands usually receive more rainfall in during the dry season than they do during the wet season. Since the clouds are higher and the water and winds are cooler and thus there is no convection during the garúa season, there is less precipitation, and usually only the highlands have moisture.

The Impact of El Niño on the Islands

El Niño can often wreak havoc on the animal populations of the Galápagos Islands. Occurring on average every four years, an caused by the reversal of the entire equatorial and atmospheric circulation pattern, El Niño causes an increase in the air and water temperatures of the islands, in addition to causing a dramatic increase in the islands' precipitation. The increase in precipitation reduces the salinity of the sea surface, and as a result, the mixed layer is too thick and the isothemes deepen. When El Niño occurs, the islands have been known to become lush, tropical isles.

Droughts and heavy rains are often associated with El Niño, and can occur at irregular and unpredictable intervals. The resulting rainfall has been known to vary tremendously. One reportclaims that the wettest year on record was 100 times wetter than the driest year on record.

Wildlife in the islands is drastically affected by the increases in air and water temperature that come with El Niño. The warmer waters kill much of the nutrient rich algae, which in turn kills many fish, as algae is their primary food source. With less fish to eat, the boobies often migrate to Peru, while many other seas birds, in addition to sea lions, and marine iguanas, see a significant decrease in populations. There have even been stories of marine iguanas dying at tourists' feet during an El Niño year. The vegetation also grows rampant and the flamingo populations increase however, as the shrimp that they feed off of thrive off of the increased water in the lagoons, and Darwin's finches were able to breed at an unusually high rate.

The animal that El Niño has the strangest effects on however, is the giant tortoise. Even slightly warmer weather than normal promotes the birth of more males, while slightly cooler weather promotes the birth of more females. Thus the warm weather that an El Niño year brings can greatly affect the gender of the giant tortoises born that year. While El Niño has been happening for years, and the giant tortoises have evolved to allow for these periodic climatic differences, the effects of global warming for instance could drastically affect the male to female ratio of giant tortoises born in the islands.

One of the worst El Niños on record was the one that occurred from 1982 to 1983. The water temperature outside or Puerto Ayora was recorded at 30° C, rushing rivers interrupted roads, and volcanic craters became freshwater lakes. The rainfall on Santa Cruz island reached 3224 mm (127 inches) for the year, as opposed to a five-year average (1965-1970) of 200 mm (8 inches) per year.

Ice Ages in the Galápagos

Most people only realize the effect of the ice caps on sea level from a global warming perspective. If global warming were to cause the polar ice caps to completely melt, then the surface level of the ocean would rise about 65m (over 214 feet). What many people fail to realize however, is that during past ice ages, enough of the Earth's surface water was frozen in the ice caps and glaciers that the sea level lowered considerably. During the last ice age, however, the sea level lowered about 120m (over 393 feet) below its present level. As a result, many of the islands of the Galápagos archipelago were probably connected, especially in the central portion of the archipelago. These connections very likely influenced the evolution of many of the islands' species as the isolation and distribution of the Galápagos species was certainly changed. Biologists studying the islands need to remember that both the islands and their climates have changed over time.

Climate Statistics

TEMPERATURESJANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC
AVG HIGH:848688868278767476777880
AVG LOW:707474727268666462646668
AVG SEA TEMP:747676767474726668707274
AVG RAINFALL: (INCHES)1121.5.75.25.50.25.50.25.50.50

Additional Reading:

Darwin, Charles. 1839. Voyage of the Beagle
The El Niño Phenomenon. Oxford: United Nations Environment Programme, 1992.
Galápagos Geology on the Web - Cornell University
Galapagos: Passenger Information, Questions & Answers pamphlet from Ecoventura S.A. Galapagos
Glantz, Michael H. Currents of Change: El Niño's Impact on Climate and Society. Cambridge: Cambridge University Press, 1996.
GORP - The Galápagos Islands
Jackson, Michael H. Galápagos: A Natural History. Calgary: University of Calgary Press, 1993.
Middleton, David W. and Pearson, David L. The New Key to Ecuador and the Galápagos. Berkeley, California: Ulysses Press, 1996.
Rachowiecki, Rob. Ecuador & the Galápagos Islands. Hawthorn, Australia: Lonely Planet Publications, 1997.
Tourism in the Submarine Platform: Galapagos Islands pamphlet