Friday, November 26, 2010


I've previously posted about the 2010 drought in Amazônia. Now, Nick Sundt at the WWF Climate Blog has assembled the science with lots of links and the results are scary. While it can not be concluded definitively that global warming is the cause, the trends are "a growing and grave concern." Here is Nick Sundt's report re-posted in full.

[UPDATE: Here's another re-post at Climate Progress with exclusive commentary by forest scientist Simon Lewis.]

WWF Climate Blog

Another Extreme Drought Hits the Amazon and Raises Climate Change Concerns

The Amazon
The Amazon region is experiencing the third extreme drought in a dozen years -- and it may turn out to be the worst on record. The droughts coupled with recent research findings, suggest that rising atmospheric concentrations of greenhouse gases will rapidly increase the frequency and severity of droughts in the region. The implications for people, biodiversity and climate are ominous.

As the map below shows, most of the Amazon region was afflicted by drought in mid-October 2010, with large areas in the north and west experiencing exceptional drought -- beyond extreme.  Drought conditions, which now are improving, have been concentrated in Brazil, but extend into parts of neighboring countries including large areas of Bolivia, Peru, Colombia.

According to the classification system used by the University College London (UCL) Global Drought Monitor, exceptional droughts normally should not occur more than a couple of times  in a century. Typical impacts include "exceptional and widespread crop and pasture losses; exceptional fire risk; shortages of water in reservoirs, streams and wells, creating water emergencies."  According to UCL,  nearly 8.7 million people live in the locations shown below (which include smaller areas outside the Amazon) that are experiencing exceptional drought conditions.

Drought in the Amazon (1 month assesment period, through 16 October 2010).  Source: University College London,
Above: Drought in the Amazon (1 month assessment period, through 16 October 2010).  Source: University College London Global Drought Monitor.

The drought results from a combination of above normal temperatures over much of the region combined with low precipitation.  As the figure below illustrates, most of the Amazon region received less than 75% of normal rainfall between 1 July and 30 September.  Large areas have received far less precipitation, in many cases less than 25% of normal.

Brazil, Percent of Normal Precipitation, 1 July - 30 September 2010.  Source: NOAA.

In a press release on 22 Oct (Seca pode bater recorde na Amazônia / Drought may hit record in the Amazon), Brazil's Amazon Environmental Research Institute (Instituto de Pesquisa Ambiental da Amazônia or IPAM) said:

"The drought of 2010 still hasn’t ended in the Amazon and could surpass that of 2005 as the region’s worst during the past four decades. In the Western Amazon, the Solimões River reached its lowest level in recorded history. In Manaus, the level of the Rio Negro (Black River) is approaching that of 1963 – the lowest in a century. Even if this doesn’t occur, the forest will have already experienced three extreme dry spells in just 12 years, two of which occurred during the past five years: 1998, 2005 and 2010. And this is not including the drought of 2007, which affected only the Southeastern Amazon and left 10 thousand sq. km. of forest scorched in the region...`The Amazon that had wet seasons so well-defined that you could set your calendar to them – that Amazon is gone,' says ecologist Daniel Nepstad of IPAM..."
Among the consequences of the drought are extremely low flows on many of the region's rivers.  On 24 October 2010, the Rio Negro, a major tributary of the Amazon, reached an all time low of 13.63 m at Manaus, edging out 1963 when water levels reached 13.64 m (Monitoramento Hidrologico: 2010, Boletim no 33 – 29/10/2010, by the Companhia de Pesquisa de Recursos Minerais or CPRM).  In contrast, just last year, the river saw an all time record high of 29.77 m as the region experienced devastating floods. (Relatorio da Cheia 2009 [PDF] [2010], by CPRM).  See photos of the flood [PDF]. Records for the Rio Negro extend back 107 years.  See also Flooding Near Manaus, Brazil, NASA Earth Observatory, 19 August 2010.

Writing for the New York Times upon his return from Iquitos, Peru, Nigel Pitman reports that "people were deeply upset by the lack of rain."  He explains: "Long dry spells like these in Amazonia wither crops and worsen air pollution and cut off whole towns from the rest of the world, when the arm of the river they’re on turns to mud. They also destroy forests" (Drought in the Amazon, Up Close and Personal, 12 November 2010).  Satellite imagery on 19 August showed a pall of smoke concentrated over Bolivia  (see Fires in South America, NASA Earth Observatory, 8 September 2010), where drought conditions allowed fires to burn out of control, prompting the Bolivian government in mid-August to declare a state of emergency.

Dr Richard Bodmer of the Durrell Institute of Conservation and Ecology (University of Kent) and the Wildlife Conservation Society recently reported on the impacts the drought is having on the Pacaya Samiria National Reserve in the Peruvian Amazon.  Among the species affected:  the pink river dolphin (see photo below).  "The conditions have resulted in fewer dolphins observed throughout the Samiria River," says Dr.  Bodmer.  "Overall, pink river dolphin numbers have decreased by 47 per cent and the grey river dolphin by 49 per cent compared with previous years' population estimates. The dolphins have been forced to leave their habitats in the Samiria River and find refuge in the larger channels of the Amazon." See Amazon drought results in dramatic fall in pink river dolphin populations (press release from Earthwatch).

Pink river dolphin (Inia geoffrensis)  in the Rio Negro, Brazil.  © Claudio Marigo / WWF.
For an outstanding series of photographs documenting the impacts of the drought, see Estiagem na Amazônia posted by Último Segundo (22 November 2010).  See also the Reuters video (6 Nov 2010) below for discussion of some of the major consequences of the drought.

Above: Brazil Looks to Ease Amazon Drought, Reuters Video, 6 November 2010.

The 2005 Drought

Just 5 years ago -- in 2005 -- the Amazon experienced an extreme drought that prompted the government of Brazil to declare a state of emergency in most of the region. In The Drought of Amazonia in 2005 (by José A. Marengo, Carlos A. Nobre, Javier Tomasella in the Journal of Climate, February 2008), researchers said:

"In 2005, large sections of southwestern Amazonia experienced one of the most intense droughts of the last hundred years. The drought severely affected human population along the main channel of the Amazon River and its western and southwestern tributaries, the Solimões (also known as the Amazon River in the other Amazon countries) and the Madeira Rivers, respectively. The river levels fell to historic low levels and navigation along these rivers had to be suspended. The drought did not affect central or eastern Amazonia, a pattern different from the El Niño–related droughts in 1926, 1983, and 1998."
“Freshwater, forest, species and local people are being heavily impacted by this drought,” said Urbano Lopes da Silva Junior, WWF-Brazil’s conservation officer based in Rio Branco in a press release at the time (Amazon Basin experiencing extreme drought, 19 Oct 2005).  “For the Amazonian population, especially the poor, the main problems are the shortage and even lack of potable water for their own consumption.”  WWF also cited the impact the drought was having on fire conditions in the region and on freshwater species such as the pirarucu, the largest freshwater fish in the world -- already a threatened species due to overfishing and destructive fishing practices.

Marengo and his colleagues in the February 2008 Journal of Climate piece (mentioned above) cited among the drought's causes "the anomalously warm tropical North Atlantic." Other researchers, in Causes and impacts of the 2005 Amazon drought (by Ning Zeng et al, in Environmental Research Letters, January-March 2008), cited a combination of tropical SSTs in both the Pacific and Atlantic:

This episode was caused by the combination of 2002–03 El Niño [in the tropical Pacific] and a dry spell in 2005 attributable to a warm subtropical North Atlantic Ocean. Analysis for 1979–2005 reveals that the Atlantic influence is comparable to the better-known Pacific linkage. While the Pacific influence is typically locked to the wet season, the 2005 Atlantic impact concentrated in the Amazon dry season when its hydroecosystem is most vulnerable. Such mechanisms may have wide-ranging implications for the future of the Amazon rainforest.
Those same elevated sea surface temperatures in the Tropical Atlantic fueled the most energetic Atlantic hurricane season on record in 2005, as well as the worst coral bleaching episode on record in the Caribbean that year.  See Status of Caribbean Coral Reefs after Bleaching and Hurricanes in 2005.
The 2005 drought in the Amazon also was notable for its impacts on the global carbon cycle.  Though the exact magnitude of the impacts are a matter of debate within the science community (see Amazon drought raises research doubtsNature News, 20 July 2010), there is evidence that the drought along with elevated air temperatures sharply reduced net primary production (NPP) in the Amazon. NPP is a measure of the amount of atmospheric carbon plants pull from the atmosphere and incorporate into biomass.  Where NPP is reduced, less carbon is fixed by plants and more is left in the atmosphere to disrupt climate.

In Drought-Induced Reduction in Global Terrestrial Net Primary Production from 2000 Through 2009 (Science, 20 August 2010)researchers using satellite data found that global NPP dropped precipitously in 2005 to its lowest level of the decade.  The largest contributor to the drop was a decline of NPP in the Amazon rainforest that they attributed largely to elevated temperatures and the severe drought.

Similarly, scientists using records from long-term monitoring plots in the Amazon reported in Science a year earlier (6 March 2009) in Drought Sensitivity of the Amazon Rainforest that the drought had a large impact on carbon flows. They note that the Amazon's old growth forests process 18 Petagrams (or Gigatons) of carbon each year -- more than twice the amount emitted annually by burning fossil fuels (1 Petagram = 1015 grams = 1 billion metric tonnes = 1 Gigaton). "Relatively small changes in Amazon forest dynamics therefore have the potential to substantially affect the concentration of atmospheric CO2 and thus the rate of climate change itself," they said.

They estimated that the drought reduced the biomass carbon balance by 1.2 to 1.6 Gigatons of carbon.  "The exceptional growth in atmospheric CO2 concentrations in 2005, the third greatest in the global record, may have been partially caused by the Amazon drought effects documented here," they add. "Amazon forests therefore appear vulnerable to increasing moisture stress, with the potential for large carbon losses to exert feedback on climate change."

The scale of such drought-induced changes in the Amazon's carbon budget can be contrasted with the magnitude of Brazil's carbon emissions from other sources, and with global carbon emissions from fossil fuels.   The Brazilian government estimates that in 2005, carbon emissions from land-use and landcover changes (including deforestation) were 1.3 gigatons of carbon and accounted for 77% of Brazil's carbon emissions from all sources in 2005  (Segunda Comunicação Nacional do Brasil à Convenção-Quadro das Nações Unidas sobre Mudança do Clima [PDF], Coordenação-Geral de Mudanças Globais do Clima, Ministério da Ciência e Tecnologia, Brasília, 2010).

That is at the low-end of the range of 1.2-1.6 gigatons of carbon that may have shifted to the atmosphere in 2005 as a result of the Amazon drought.  In other words, 2005 carbon emissions associated with the drought may have equaled or  exceeded those from deforestation in Brazil that year.  Furthermore, at the global level, the range of emissions that may have resulted from the 2005 drought is equivalent to roughly 16-22% of annual global carbon emissions from fossil fuel use in 2005 (about 7.4 gigatons of carbon).

The 2010 Drought

Just as the 2005 drought was preceded by an El Niño (from Apr-May-June 2002 through Feb-Mar-Apr 2003), the 2010 drought was preceded by an El Niño (May-June-July 2009 through March-April-May 2010).  Consequently, the Amazon experienced well below normal precipitation during the rainy season that normally stretches roughly from September-November through March-May.  The National Oceanic and Atmospheric Administration reported in The South American Monsoon System Summary, July 2009-June 2010  [Powerpoint] that precipitation from July 2009 through June 2010 was well below normal over the Amazon basin, consistent with the expected impacts of an El Niño.  Furthermore, precipitation was much lower than during the 2002-2003 rainy season associated with the 2002-2003 El Niño that set the stage for the 2005 drought.

Similarly, as in 2005, sea surface temperatures (SSTs) in the tropical North Atlantic ocean in 2010 were elevated during the dry season (normally April-September). The maps below show the global temperature anomalies for September 2005 and September 2010 (around the usual end of the dry season) and show that SSTs in the north tropical Atlantic and the Caribbean in both years show a similar pattern.  Likewise, the surface temperatures over the Amazon during both years were elevated -- though were substantially higher in 2010.

 September 2005 surface temperature anomalies.  Source: NASA
Global Surface Temperature Anomalies, September 2010. Source: NASA.

The Monthly Tropical North Atlantic Index (TNA) (a measure of the average monthly SST anomaly in the region) has been at record high levels (and above the values for 2005) for every month of 2010 through September.  The TNA for October was second only to that of 2003. The separate Caribbean SST Index (CAR) has not been at record levels for most months, but has been anomalously high and for most months has been above 2005 levels.

For both the TNA and the CAR indices, the long term trend is upward.  See for example the long-term trend for the Tropical North Atlantic Index for the month of September below.

Above: The North Tropical Atlantic SST Index for the Month of September, 1951-2010.  SST anomalies (relative to 1951-2000) averaged over the region of the tropical Atlantic between Africa and the Caribbean (the region is indicated by NTA on this map) for the month of September from 1951 through 2010.

As in 2005, these high SSTs in the Tropical North Atlantic are resulting in one of the worst coral bleaching episodes on record in the Caribbean, as well as energizing one of the most active Atlantic hurricane seasons on record.  See our recent posting, Sea Surface Temperatures in Tropical North Atlantic Rise to Record Levels in 2010, With Impacts from the Amazon to Canada (16 November 2010).

Are the high SSTs -- as in 2005 -- also associated with the Amazon drought conditions during the 2010 dry season?  The answer is most likely "yes," but the nature of the connection and the role of other factors (such as the 2009-2010 El Niño in the tropical Pacific) will have to await the published research results of scientists.  Similarly, we will not know the impacts of the 2010 drought on the cycling of carbon to and from the Amazon until scientific assessments are conducted and research results are published.

The Climate Change Connection

What connection might these droughts have to rising concentrations of GHGs in the atmosphere and what might we expect during the course of this century as GHG  concentrations continue to rise?
The connections between rising GHG concentrations on the  El Niños is a matter of scientific interest and debate.  El Niño-Southern Oscillation patterns in the tropical Pacific appear to be changing and some research suggests the changes may be related to climate change (see El Niño in a changing climate, Nature, 24 September 2010).  However, the science is very much unsettled, so we cannot say anything definitive about the relationship between rising GHGs and the El Niños that preceeded the 2005 and 2010 droughts.

In the case of rising SSTs in the tropical Atlantic -- another major contributor to the 2005 drought and likely to the 2010 drought  --  the connection to rising GHG concentrations is better understood, though there is uncertainty regarding the magnitude of the impact relative to other variables.

When asked about the degree to which rising GHG concentrations in the atmosphere were contributing to the trend of rising  sea surface temperatures in the tropical North Atlantic Ocean, Greg Holland of the National Center for Atmospheric Research (NCAR) said at a Congressional briefing on 30 June 2010 that the temperatures could not be explained without accounting for rising GHG concentrations.  He said that while some researchers thought the rising GHG levels might account for 60-80% of the temperature anomaly, he estimated that about half was due to rising GHGs.

This is consistent with research results published in Geophysical Research Letters on 29 April 2010.  In Is the basin-wide warming in the North Atlantic Ocean related to atmospheric carbon dioxide and global warming?, Chunzai Wang and Shenfu Dong of NOAA's Atlantic Oceanographic and Meteorological Laboratory, conclude that "both global warming and AMO [Atlantic multidecadal oscillation] variability make a contribution to the recent basin-wide warming in the North Atlantic and their relative contribution is approximately equal."

If the rise in SSTs in the tropical north Atlantic are being driven in part by rising GHG concentrations in the atmosphere, and if those SSTs are implicated in the Amazon drought of 2005 and potentially in the drought of 2010, then rising GHG concentrations are among the factors likely contributing to those droughts. However, researchers have not at this point definitively attributed either drought to rising atmospheric GHG concentrations.

More importantly rising atmospheric concentrations of GHGs in the future will continue to affect tropical sea surface temperatures in both the Pacific and the Atlantic,  and research indicates that this -- in combination with rising air temperatures over the Amazon -- will increasingly dry out the Amazon. In Amazon Basin climate under global warming: the role of the sea surface temperature (Philosophical Transactions of The Royal Society B, Biological Sciences, 27 May 2008), researchers analyze these connections.

Using a model from the UK's Hadley Centre, they focused on a period centered around the year 2050.  The analysis suggests that SST anomalies in both the tropical Atlantic and Pacific would combine to reduce Amazon Basin rainfall, "leading to a perennial soil moisture reduction and an associated 30% reduction in annual Amazon Basin net primary productivity (NPP). A further 23% NPP reduction occurs in response to a 3.5°C warmer air temperature associated with a global mean SST warming."

In Drought under global warming: a review (Wiley Interdisciplinary Reviews: Climate Change, 19 Oct 2010) Dr Aiguo Dai of the National Center for Atmospheric Research says that models used by the Intergovernmental Panel on Climate Change in its 2007 assessment "project increased aridity in the 21st century, with a striking pattern that suggests continued drying" over many land areas including "most of Americas."  While acknowledging the uncertainties, he says that the model results appear "to be a robust response to increased GHGs."  He adds: "This is very alarming because if the drying is anything resembling [the model results]...a very large population will be severely affected in the coming decades" in Brazil and many other land areas.

Approaching -- or passing -- a Tipping Point

The possibility of increasingly arid conditions along with more frequent extreme droughts in the Amazon -- and the regional and global implications -- is a matter of growing and grave concern.  In a report to WWF, The Amazon's Vicious Cycles: Drought and Fire in the Greenhouse [2.49 MB pdf] (Dec 2007, WWF), IPAM's Daniel Nepstad concludes:

"Synergistic trends in Amazon economies, vegetation, and climate could lead to the replacement or damaging of more than half of the closed-canopy forests of the Amazon Basin over the next 15 to 25 years, undoing many of the successes currently in progress to reduce global emissions of greenhouse gases to the atmosphere. Counteracting these trends are emerging changes in landholder behaviour, recent successes in establishing large blocks of protected areas in active agricultural frontiers, important market trends favouring forest stewardship, and a possible new international mechanism for compensating tropical nations for their progress in forest conservation, that could reduce the likelihood of a large-scale dieback of the Amazon forest complex. In the long term, however, the avoidance of this scenario may depend upon worldwide reductions of greenhouse gas emissions that are large enough to prevent global temperatures from rising more than a degree or two."
More recently (in late 2009 and before the 2010 drought), in Major Tipping Points in the Earth’s Climate System and Consequences for the Insurance Sector [PDF], WWF identified the prospect of more frequent extreme droughts in the Amazon and the related rainforest dieback as being among the "tipping points" that could be passed in coming decades, with "significant impacts within the first half of this century." 

Given the current drought in the Amazon, the report's discussion of the 2005 Amazon drought should raise some eyebrows:

"...until more recently, 2005-like droughts may have had a frequency of between 1-in-40 and 1-in-100-years. Recent work, however, suggests that, with the now elevated concentration of GHGs  [greenhouse gases] (currently ~430 ppmv CO2e [parts per million, volume, of carbon dioxide equivalent],compared with 280 ppmv CO2e pre-industrial), the return period is of the order of 1-in-20-years and this is likely to increase to 1-in-2 and above by between 2025 and 2050 if stabilization at 450 to 550 ppmv CO2e is achieved (with a higher probability if it is not)."
Given that the 2010 drought is comparable to the 2005 drought -- and that they are only five years apart, we already may be closer to a return period of 1-in-2 years than the research suggested.
About the implications of an increase in the frequency of 2005-like droughts, the report says:

"The 2005 drought impacts were relatively severe. However, the social, environmental and economic consequences of such a significant increase in the frequency of 2005-like events are far more than the sum of 2005 impacts x drought frequency. What is currently termed ‘drought’, with such a significant increase in frequency, becomes the norm implying a potentially radical change in hydrological systems in affected regions, with knock-on effects for people, environment, and economy."


For an excellent discussion of the 2005 and 2010 droughts, climate change and the implications for the Amazon, see the video below from GlobalPost, Rumble in the Jungle: Is the Amazon Losing the Fight Against Climate Change? by Erik German and Solana Pyne

See also their online article, Rivers run dry as drought hits Amazon (GlobalPost, 3 November 2010).


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