El Niño in 1982 - 83
The El Niño of 1982-83 brought changes that in certain cases can still be observed by CDRS and some researchers. The following paragraphs detail some of these changes.
Visitor sites
Some visitor sites in Galápagos National Park became inaccessible due to the exuberant growth of vegetation, the destruction of paths and the lack of safety at landing sites (Smith, 1999). Additional factors such as an increase in populations of the stinging little fire ant (Wasmannia auropunctata).
Fauna
The fauna of Galápagos was affected in various ways be the El Niño event of 1982-83. Some birds and marine mammals, as well as marine iguanas, suffered visible decreases in their populations (Gibbs et al, 1987; Toepfer, 2007). According to Toepfer (2007), it is principally due to the following factors: (i) mortality, especially caused by the absence of food and by increased incidence of illness; (ii) reproductive failure, probably related to lack of food; (iii) displacement to other locations. The effect was particularly notable in the colonies of blue-footed boobies (Sula nebouxii) on Española Island, in the populations of endemic flightless cormorants (Nannopterum harrisi) and Galápagos penguins (Spheniscus mendiculus), as well as in the populations of marine iguanas (Amblyrhyncus cristatus) throughout the archipelago (Gibbs et al, 1987).
Flora
Immediate effects were noted in the vegetation of the Galápagos Islands, where plant populations exploded in normally arid areas and demonstrated unusually rapid and exuberant growth in the highlands of some islands (Smith, 1999; Holmgren et al, 2001). Research carried out in the months following the end of the 1982-83 El Niño event showed that the abundance and distribution of various species of plants than on their numbers; the conclusions of these studies indicated that no long-term effects were expected in some species (Smith, 1999). However, there would be alterations in the type of vegetation in certain ecosystems.
Changes in the vegetation varied according to the life zone and type of plants present. Generally, species of the arid zones reacted with much greater speed to the abundance of rainfall. Herbs and climbing plants particularly took advantage of this new resource and expanded very rapidly (Smith, 1999). Similarly, enhanced germination occurred in seeds that had apparently been dormant in the soil for several months or years (Smith, 1999). Based on the research of Smith (1999), notable mortality occurred among adult individuals of the giant cacti in the genus Opuntia, as well as large Scalesia trees, which could not support their weight when their roots rotted due to excessive rainfall. As a result of accelerated growth rates measured by Holmgren et al (2001), plants in the most humid zones were less sensitive to increased precipitation than were plants in the arid. As in the arid zones, those humid zone species that benefited most from increased precipitation were herbs and climbers. Again, Scalesia was the genus that suffered greatest mortality of adult individuals.
Introduced organisms
During the 1982 - 83 El Niño event, observers noted increased abundance of introduced organisms that depend on the quantity of precipitation, such as the little fire ant Wasmannia auropunctata (Wetterer et al, 2003). The little fire ant demonstrated a particularly elevated rate of expansion, moving north on Santa Cruz Island at the rate of approximately 0.5km per year. Besides, the number of introduced rat (Rattus rattus) increased markedly in areas of the islands populated by humans (Abdelkrim, 2005).
Niño Regions
Scientists have identified five regions in the equatorial Pacific that they consider to be worthy of special attention with regard to the observations and monitoring of El Niño processes. Their locations are shown in Figure AAA. Researchers are increasingly focusing on environmental changes in the Niño3.4 region in order to identify the onset of an El Niño event. Each region provides different kinds of information about either El Niño or the Southern Oscillation.
Figure AAA. Map depicting four regions in the equatorial Pacific Ocean identified as important locations for monitoring the wind and sea surface temperature changes associated with the El Niño process. Source: Australian Government Bureau of Meteorology (2011).
Niño1 is the region of coastal upwelling off the coasts of Peru and Ecuador. It is sensitive to changes in the ocean and the atmosphere, both seasonally and especially during El Niño episodes. Coastal upwelling processes in Niño1 are particularly sensitive to changes in air-sea interaction in the central and eastern equatorial Pacific.
Niño2 represents the Galapagos Islands region of the equatorial Pacific. Equatorial upwelling processes in this area are also sensitive to seasonal, as well as El Niño-induced, changes in the marine environment. Niño2 is a transition zone between the central and eastern equatorial Pacific, sensitive to changes in either Niño1 and Niño3, or both.
Niño3 is in the central equatorial Pacific, where there is a large El Niño signal but not much sensitivity to seasonal changes in air-sea interaction. It is in this region where information on changes in surface wind has been used by Mark Cane and Stephen Zebiak to project the likely onset to El Niño events. According to Cane (1991), "a warming in this region is thought to influence the global atmosphere strongly. It is probably the best single indicator of an ENSO episode likely to affect global climate".
Niño3.4 is relatively new region in the tropical Pacific increasingly used by more researchers to correlate changes in sea surface temperatures and surface winds there to climatic anomalies around the globe. Many researchers now use changes in Niño3.4 instead of Niño3 in their El Niño forecast modeling activities. It overlaps the Niño3 and Niño4 regions, as shown in Figure AAA.
Niño4 encompasses part of the western equatorial Pacific known as the warm pool. Here, sea surface temperatures are the highest in the Pacific. During an El Niño event, there is a relatively small change in sea surface temperatures (cooling). However, that small change is important, because the warmest water at the ocean's surface and the cloud producing processes that tend to follow it move away from the western Pacific toward the central and eastern Pacific. Hence during El Niño there are dry conditions in several countries in the western Pacific and very wet conditions in northern Peru and southern Ecuador.
Australia has suffered severe droughts in its northern and eastern regions during many El Niño years. These droughts have reduced crop yields, killed livestock, eroded soils and encouraged destructive bush fires.
澳洲代写作业 El Nino In The Galapagos Biology Essay
