Background

Data query and download

The Galapagos terrestrial climate is atypical for its equatorial location: particularly the prolonged cool season with dry conditions over most of the archipelago. Ocean currents and winds interact to define the two seasons. The hot season generally prevails from January to May (Figure 1a & Figure 2), characterized by elevated sea and air temperatures, and convective rainfall that is highly variable in correlation with sea surface temperatures. During the cool season, usually from June to December (Figure 1b & Figure 2), cooler temperatures and a misty “garúa” cloud layer persistin which orographic, or highland, rainfall results in steady precipitation in the higher windward sides of the islands and almost no rainfall in the rest of the archipelago. This creates two broad climatic zones: the humid highlands and dry lowlands, with an intervening transition zone (Figure 3). Climatic conditions throughout the year are summarized in Figure 4. Climatic data for highland and lowland sites on Santa Cruz Island are available for query and download here.

Figure 1a - Landsat satellite imagery over western Galapagos Figure 1b - Landsat satellite imagery over western Galapagos

Figure 1: Landsat satellite imagery over western Galapagos showing typical cloud formations in the (a) hot season, 11 Jan 2010 and (b) cool season, 25 Nov 2009.

Figure 2 - Hot and Cold Seasons in Galapagos

Figure 2: The hot season occurs in the first half of the year and the cool season in the second half of the year; but both seasons are variable in length. A hotter hot season is likely to be longer; starting earlier than average (even in the previous year) and finishing later. A cooler hot season is likely to be shorter.

Galapagos is strongly influenced by the El Niño Southern Oscillation (ENSO). ENSO causes extreme events in Galapagos every 2-7 years (although without periodicity); either warm (El Niño) or cool (La Niña). Strong El Niño events cause higher than normal sea surface and air temperatures during the hot season, with an associated increase in rainfall. Biological productivity drops dramatically in the marine realm, causing widespread mortality, while productivity greatly increases in the terrestrial environment. Two strong El Niño events in 1982-83 and 1997-98 greatly affected both the terrestrial and marine ecosystems of Galapagos. La Niña events cause lower than average sea surface and air temperatures and reduced rainfall in the normally wet hot season. The strength of the ENSO influence is illustrated by annual rainfall totals. The maximum annual rainfall recorded at the Charles Darwin Research Station (CDRS) on the Galapagos island of Santa Cruz was 2769 mm in the El Niño year of 1983, and the minimum annual rainfall was 64 mm during the subsequent La Niña event in 1985 (Table 1). Rainfall records since 1964 are available for query and download here.

Table 1 - Summary rainfall statistics (mm) for the Charles Darwin Research Station(CDRS) and Bellavista

Table 1. Summary rainfall statistics (mm) for the Charles Darwin Research Station(CDRS) and Bellavista. Median (the middle value) is a better indication of general rainfall than average when rainfall is so highly variable. Rainfall records are available for query and download here.

Figure 3 - The climatic zones in Galapagos

Figure 3: The climatic zones in Galapagos

Figure 4: Annual variation in climate variables in Galapagos over the period 1965 to 2009 recorded at the Charles Darwin Research Station (CDRS) in Puerto Ayora, Santa Cruz(tan), representing the dry lowlands, and in the village of Bellavista (green) representing the humid highlands. Sea surface temperature (SST) is expressed as monthly averages recorded at the CDRS, with error bars depicting the variation (standard deviation). Monthly air temperature bars indicate average daily minimum and maximum. Wind speed is the monthly average of daily recordings at the CDRS (base of arrow) with arrows showing predominate wind direction for each month. Sunshine and humidity are expressed as monthly averages of daily recordings, and number of rain days as the median (middle value) of all years. Rainfall bars show median monthly totals, with error bars depicting the variation (interquartile range). Climatic data for CDRS and Bellavista are available for query and download here.


This information is based on the paper by Trueman & d'Ozouville (2010) in Galapagos Research, available here.

Key scientific articles on climate:

  • Bush, M. B., P. A. Colinvaux, M. Steinitz-Kannan, J. T. Overpeck, J. Sachs, J. E. Cole, Collins, J. L. Conroy, and A. Restrepo. 2010. Fortyyears of paleoecology on the Galapagos. Galapagos Research, No. 67: In Press.
  • Huttel, C. 1995. Vegetación en coladas de lava. ORSTOM y Fundación Charles Darwin, Quito, Ecuador.
  • Robinson, G., and E. del Pino. 1985. El Niño in the Galápagos Islands: The 1982-1983 event. Charles Darwin Foundation, Quito, Ecuador.
  • Sachs, J., S. N. Ladd, J. E. Cole, P. Goyes, D. Manzello, R. Martinez, C. Palacios, G. A. Vecchi, and L. Xie. 2010. Expected changes in the climate and oceanography of the Galapagos in the 21st century. Galapagos Research, No. 67: In Press.
  • Snell, H., and S. Rea. 1999. The 1997-1998 El Niño in Galápagos: Can 34 years of data estimate 120 years of pattern? Noticias de Galapagos No. 60:11-20.
  • Trueman, M. and d’Ozouville, N. 2010. Characterizing the Galapagos terrestrial climate in the face of climate change. Galapagos Research, No. 67.