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