Discussion of Climactic Drivers of Drought in Amazonia and the Observed Effect

Hanna Link

10/31/12

Discussion of Climactic Drivers of Drought in Amazonia and the Observed Effect

According to the United States Geological Survey, drought is “a period of below average water content in streams, reservoirs, groundwater aquifers, lakes and soils.” I will discuss the climactic factors which contribute to drought in the Amazon region of South America. Then I will talk about drought effects on the ecology of Amazonia, specifically during the 2005 and 2010 major droughts.

Complex climactic factors contribute to droughts in the Amazonia region of South America. On an interannuel time scale, El Nino or Southern Oscillation events (ENSO) force the relative precipitation in parts of the Amazon area. (3). In El Nino years, eastern Pacific Ocean sea surface temperatures rise, which forces a decrease in precipitation over the north-central and eastern Amazon regions (4).

Also, the Intertropical Convergence Zone (ITCZ), influences dry season rainfall in Amazonia. The ITCZ location depends upon the intensity of the north-south Atlantic gradient. The North Atlantic Oscillation and the Atlantic Multidecadal Oscillation influence the sea surface temperatures in the north Atlantic. When sea surface temperatures rise in the north Atlantic Ocean more than in the south Atlantic, the gradient shifts northwards. As the gradient moves northwards, the ITCZ shifts northwards too (3). A northward shift of the ITCZ significantly weakens the northeast trade winds which carry the moisture from the tropical Atlantic to the Amazon region, which produces drought in the western and southern regions (4). Thus, climactic factors govern drought in Amazonia, like warm Pacific ocean temperatures and their effect on El Nino events, and warm north Atlantic temperatures and their ultimate effect on local trade winds.

The Amazon Rainforest responds in varying ways to drought. The most recent research has been produced from the major droughts in that region during 2005 and 2010. First, the 2005 drought was linked with increased sea surface temperatures in the north Atlantic (4). This drought affected mostly the southwestern Amazon (7). Contrary to model predictions, this drought produced an overall “greening” of the affected area in a study done by Saleska. Previous models predicted forest collapse due to the amplification of the forest’s physiological response to less water, while the observed affect on the Amazon from field research showed that a decrease in water was not extremely problematic because the trees of the Amazon have deep roots. Instead, the 2005 drought showed “greening” of the canopy due to an increased availability of sunshine (6). Oppositely another study found only half of their observed plots gained biomass, and so concluded that Amazon forest productivity during the 2005 drought had dropped (5).

Second, the 2010 drought impacted almost all of “South America’s tropical region south of the equator” (7). Like the 2005 drought, the one in 2010 was linked to high Atlantic sea surface temperatures (2). This drought was 1.65 times larger than the 2005 drought. Furthermore, while the 2005 drought showed some greening, the drought of 2010 showed four times more browning than in 2005. According to one study, 14% of the drought affected forest showed browning in 2005, whereas 51% of drought affected forests showed browning in 2010 (7).

To conclude, multiple climactic factors force drought in the Amazon region. The major droughts of 2005 and 2010 were linked with high sea surface temperatures in the north Atlantic ocean. The 2010 drought was more intense than the 2005 drought.

Works Cited

"Definitions of Drought." Water Information. United States Geological Survey, 6 Aug. 2012. Web. 28 Oct. 2012. .
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Saleska, S. R., K. Didan, A. R. Huete, and H. R. Da Rocha. "Amazon Forests Green-Up During 2005 Drought." Science 318.5850 (2007): 612.
Xu, Liangu, Arindam Samanta, Marcos H. Costa, Sangram Ganguly, Ramakrishna R. Nemani, and Ranga B. Myneni. "Widespread Decline in Greenness of Amazonian Vegetation Due to the 2010 Drought." Geophysical Research Letters 38 (2011): n. pag.