Final thoughts

This should be my final post. Instead of writing about any paper in specific, I think it would be more fruitful if I wrote about some of my conclusions regarding the topic of extreme climate change in the Amazon Rainforest. First of all, the Amazon can apparently really take a beating. It has been around for millions of years (exactly how many is more difficult to determine), and survived extreme changes in climate over prolonged periods of time, including the last glacial maximum. Therefore, gradual shifts in temperature and precipitation, while affecting the forest, historically do not seem to pose a threat to its existence.

However, this does not mean, by any stretch of the imagination, that the Amazon Rainforest is safe. First of all, current levels of carbon dioxide and human impact have no historical precedent, so while there may be some comfort in realizing how resistant the rainforest has been, it is outweighed by how much the rainforest has suffered since the industrial era. Secondly, the current changes in precipitation and increased seasonality also lack a clear precedent in the history of the Amazon, as do El Niño/La Niña events. Finally, while the potential effects of current human impact and global climactic conditions are already difficult enough to comprehend, unless there are significant changes, these conditions will only become more extreme and further away from any precedent.
While nobody can predict the future, and historical analogues are at most helpful suggestions as to what may happen, what is certain is that anthropogenic effects on the Amazon can and have been damaging to the forest. While studies with models to predict the future of the rainforest and neighboring ecosystems paint several different pictures of what tomorrow might be like, they also reflect the degree of uncertainty towards the upcoming decades and centuries. Studies can become more in depth, and models more accurate, but it does not change what is already known and certain, that humans are destroying the Amazon. Burning, cutting, and polluting the forest are all clearly and unequivocally harmful. These actions are most realistically within the control of people and governments, and can be changed so as to mitigate any effects on the climate of the Amazon, not to mention the physical dimensions of the forest.

Which question is more important? If the resilient past of the Amazonian Rainforest will guarantee its future, or if we are willing to pay the price to find out?

The Amazon, past and future

I found a paper that tries to present information about the Amazon from when it (arguably) began, up until its present and potential future. It is called “New Views on an old forest: assessing the longevity, resilience and future of the Amazon rainforest”, by Maslin et al., and the authors use palaeoclimate and palaeoecoecological records to determine exactly how far back the Amazon’s existence can be traced.

They argue that the Amazonian rainforest “has been a permanent feature of this continent for at least the last 55 million years”, meaning it has been around since at least the late Cretaceous. However, the definition of what a rainforest is today does not match up with what “rainforests” were millions of years ago, and the paper uses “megathermal moist forests” (MTMF) as a more precise term for discussing the evolution of what would eventually become modern rainforests.

Fig. 1 Reconstructions of the exposed land masses and occurrence of megathermal moist forests for six key periods. Arrows indicate possible dispersal of rainforest taxa

In the past 55 million years, tropical rainforests have existed in more parts of the globe than they do today, and their growth was subject to upper and lower boundaries in temperature and moisture similar to what those of rainforests today. These conditions exist today within the tropics, and in earlier stages of the earth existed in different latitudes and with different expansion. However, the evidence put forth by the authors is that the region where the Amazon rainforest exists today has been continually covered in MTMF throughout the whole period.

There is a third condition (besides temperature and precipitation) that is discussed, and it is levels of atmospheric carbon dioxide. There have been great fluctuations in the quantity of carbon dioxide released into the atmosphere, and the authors cite a paper by Chambers and Silver 2004, that, among others, that show that plants grown under double current carbon dioxide levels grow faster. However, they are careful to note that this does not mean that greenhouse gases are going to necessarily help forests grow. There are certain kinds of plans that are favored by different levels of carbon dioxide, and therefore if carbon dioxide levels were to double, certain plants would probably grow better, while others would be put under tremendous strain. Overall, this would endanger the balance of the Amazonian rainforest, and is unfavorable.

Fig 2. Reconstructions of past atmospheric CO2 levels over the last 600 Ma using modelling, paleosols, algae and foraminifera carbon isotopes, stomata density and boron isotopes. These are compared with global temperatures, mean tropical temperature variation and the extent of continental glaciation.

The article then goes on to discuss the future of the Amazon, and they use what I consider to be one of the most eloquent in summing up our current situation, since “we are entering a non-analogue future”. Global climate change will spur changes within the rainforest, and in turn these changes will affect regional, and consequentially, global climate. However, it is very difficult to predict what may happen. The authors of this paper focus on the same factors that allow the Amazon to exist to try and imagine what can happen in the coming centuries. With rising world temperatures, deforestation, and carbon dioxide levels, the Amazon rainforest runs the risk of disappearing within one century. The primary problem is human impact, but then the reactions of the forest to these impacts are another problem unto their own, and are, as the paper describes, “poorly understood threats”. With no past analogue to base estimates on, the consensus seems to be that mitigating negative human impact is the world’s safest bet.

Sources: Maslin, M.A., Y. Mahli, O. Phillips and S. Cowling “New views on an old forest:assessing the longevity, resilience and future of the Amazon Rainforest.” Transactions of the Institute of British Geographers 30, 4, 390-401 (2005)

 

The Amazon since the Last Glacial Maximum

For this post I read a very interesting article published in 2004 called “Responses of Amazonian ecosystems to climatic and atmospheric carbon dioxide changes since the last glacial maximum” by Mayle et al., published by The Royal Society. In it, the authors do not do any original data collection, but instead choose to analyze several already existing papers and data in order to try and paint a more comprehensive picture regarding Amazonian ecosystems since the last glacial maximum. They also go one step further and use these findings to try and predict what could be in store for the near future of the Amazonian Rainforest.

As mentioned in a previous post, the authors disagree with the possibility of the rainforest having been reduced to separate islands, as “both fossil pollen data and dynamic, process-based vegetation simulations show that most of the Amazon Basin remained forested at the LGM”. As a whole, the forest expanded after the LGM, retracted in the early to mid-Holocene due to decreased precipitation, increase in temperature, and lower carbon dioxide levels in the atmosphere. Finally, in the late Holocene the forest began to expand once again, until significant human effects kicked in and we began to make the forest shrink once again.

Figure 1. (a) Map showing the location of sites discussed in the text. The shaded area shows the current distribution of humid evergreen broad-leaf forest (rainforest). The hatched area shows the Andes mountains. Lowland unshaded areas represent seasonally dry forests and savannahs. (b) Schematic broad-scale summary trends of climatic change and/or vegetation response for each site since 21 000 cal yr BP.

The most noticeable changes, in terms of vegetation replacement such as rainforest by savannah, would have taken place in ecotonal regions. Therefore, while the Amazon Rainforest as an integrated body was most likely intact, the boundaries of the forest did change. Not only between the rainforest and savannah, but also between the rainforest and Andean cloud forests.

However, what I found to be by far the most interesting proposition of this paper is that perhaps the savannah vs. forest replacement concept is flawed. Nowadays, in the east of Brazil there are Caatinga forests, classified as seasonally dry forests. So while there seems to be a consensus that the Amazon was never replaced by savannah since the LGM, parts of the forest could have become seasonally dry. The authors of this paper mention widely-separated semi-deciduous/deciduous forests with common species, namely the Caatinga forests in the east of Brazil, Chiquitano dry forest of eastern Bolivia and the Andean piedmont dry forest in south Bolivia/northwest Argentina.

The pollen records that were always assumed to indicate the presence of a Rainforest, could just as easily indicate a primarily dry forest region. However, the similarity of these signals brings forth this possibility, but also makes it very difficult to determine the case one way or another. The authors mention efforts towards this goal, but no definitive answer has been reached. At least from what I have read, this hypothesis is at the very least plausible, not to mention very interesting.

Figure 3. SDGVM model simulations forced with the UGAMP GCM. See § 2d(i). Key: c3, C3 grasses; c4, C4 grasses; ebl, evergreen broad-leaf forest; enl, evergreen needle-leaf forest; dbl, deciduous broad-leaf forest; dnl, deciduous needle-leaf forest. Amazonian vegetation distribution: (a) Pre-Industrial; (b) Mid-Holocene; (c) LGM; NPP of Amazonian vegetation: (d) Pre-Industrial; (e) Mid-Holocene; ( f ) LGM. (t C ha_1 yr_1, tonnes of carbon per hectare per year, where 1 hectare is 104 m2.)

After analyzing a wide array of data, the paper then goes on to propose what might happen to the Amazon Rainforest in the years to come. Since there is likely to be a rise in temperature and decrease in precipitation, both likely to be aggravated by deforestation, proxy data suggests there will be more frequent wide-spread fires, leading to a replacement of current vegetation to more drought and fire tolerant vegetation, typical of savannah-type ecosystems. However, the big wild card is carbon dioxide levels, since there is nothing in the past to compare them to, especially if they reach the projected levels of twice those of the mid Holocene by the year 2050. I do not have a tremendous amount of faith in the ability of past records to accurately predict what is to come, simply because I firmly believe that, given how different the world has become since the Industrial Age, there are more factors than carbon dioxide levels which make the future difficult to model based on proxy data. One example of this, which I have discussed in previous posts, is the increasing seasonality of climate in the Amazon, which is not the same as average temperature and precipitation changes over time, considering there can be extreme variability between seasons and yet no change to the observed average yearly values.

Sources: Responses of Amazonian ecosystems to climatic and atmospheric carbon dioxide changes since the last glacial maximum, Francis E. Mayle, David J. Beerling, William D. Gosling, Mark B. Bush, Phil. Trans. R. Soc. Lond. B March 29, 2004 359:499-514; doi:10.1098/rstb.2003.1434

The Amazon in the Late Quaternary

For this post I read a paper titled “Late Quaternary Vegetation Dynamics in the Southern Amazon Basin Inferred from Carbon Isotopes in Soil Organic Mattter”, by Freitas et al., which analyzes, as the title states, carbon isotopes of soil organic matter (SOM) extracted from a 200km transect of a region in Brazil that is composed of savannas surrounded by forests. The objective of this study is to determine what kind of vegetation was previously present in this location.

 Fig. 1 Schematic diagram of the vegetation distribution and sample sites. Single lines, forest; double lines, savanna; arrows, sites of sample collection. Sample sites are identified by the distance along BR 319, from km 0 (Porto Velho) to km 200 (Humait´a).

However, I do need to point something out about this article before I go on. It was published in 2001, and for this reason the authors still entertain the hypothesis that, as our very own Mackay puts it “during intervals of full glacial conditions, increased aridity resulted in the Amazon rainforest being restricted to isolated pockets, surrounded by expanded savannah environments”. However, as Mackay’s chapter goes on to explain, this hypothesis is at odds with palaeoecological evidence, which suggests that forests made it through time periods of full glacial conditions.

Fig. 2 The ±13C range of the C3 and C4 plant species collected at: (a) km 46 (f); (b) km 142 (f); and (c) km 188 (s). The three sites have some common plant species.

The study does not lose its relevance because of this, I merely point it out as the authors mentioned this debate in the paper, and it no longer seems to be much of a debate. This study nonetheless still has valid results is that the geographical area being analyzed has well-defined natural boundaries between savanna and forest. The carbon isotopes showed that at least in this location, there were shifts between forest and savanna vegetation. From 17,000 and 9000 ¹⁴C yr B.P. the entire area was a forest, then from 9000 to 3000 ¹⁴C yr B.P. it was a savanna, and then after 3000 ¹⁴C yr B.P. there was forest expansion once again to the present mixed state. The authors also propose that the forest-dominated periods probably correlated with a wetter climate, and a drier one for the savanna-dominated time frame. They also recognize that while these results cannot say much about the changes in regional vegetation change due to past climate change, it does indicate that the Amazon rainforest has receded and expanded in at least some areas.

Sources: De Freitas, H. A., Pessenda, L. C. R., Aravena, R., Gouveia, S. E. M., De Souza Ribeiro, A. & Boulet, R. 2001 Late Quaternary vegetation dynamics in the southern Amazon Basin inferred from carbon isotopes in soil organic matter. Quatern. Res. 55, 39–46.

Mackay, A. W. (2009) - An introduction to Late Glacial-Holocene environments. In S. T. Turkey (Edt.), Holocene Extinctions, Oxford University Press, Oxford, 1-15.

Amazon basin rainfall variability

In the study “Spatio-temporal rainfall variability in the Amazon basin countries” by Villar et al., 756 pluviometric stations throughout Brazil, Peru, Bolivia, Colombia, and Ecuador were used to analyze rainfall variability in the period ranging from 1964 to 2003. What distinguishes this study from previous ones is that it includes significant data from areas other than the Amazon forest within Brazil, which tends to have the most data since most of the forest lies within its borders.

The study confirmed the fact that there are not only great differences in rainfall between the Amazon basin and other surrounding ecosystems, but also within the basin itself. As mentioned in previous posts, the differences lie between north and south, and east and west, with the wetter areas (generally) towards the north and west. However, the more interesting findings are in relation to rainfall changes over the second half of the 20^th century. The study is careful to mention that there is much disagreement with regard to whether the forest is getting drier or wetter, and cites papers that attempt to solve this question. But in favor of the paper at hand, the authors use a larger amount of pluviometric stations over a larger area, and also seek to analyze changes over a longer period.

Figure 1. Mean 1975–2003 annual rain (mm/year). The pluviometric stations mentioned in the text are indicated. Andean regions above 500 m are limited by a black and white line.

They found that there is an average decrease in rainfall at a rate of -0.32% from 1975 to 2003, and that “the decrease has been particularly important since 1982”. So, in essence, the forest as a whole is getting drier, or at least receiving less rainfall. But, in the same way there are great differences in how much water the forest receives according to different regions, the changes in rainfall trends are also region-specific. In the 1970’s and 1990’s, in the wet season there was more rainfall in the northwest of the forest, and less in the southeast. In the 1980’s, the opposite was true. Also, up until 1992, rainfall was decreasing more significantly in the dry season, and also decreasing but not as much in the wet season. Since 1992, the wet season has seen an increase in rainfall, and the dry season continues to become drier.

Figure 2. (a) 1975–2003 evolution of the average annual rainfall (mm) in the Amazon basin at the delta and trend line (significant at the 99% level). (b) 1975–2003 evolution of the average quarterly rainfall (mm) in the Amazon basin at the delta and trend lines DJF, JJA, and SON have significant trends at the 95, 90, and 99% levels, respectively. In MAM there is no significant trend.

In context with my other posts about extreme droughts and flooding, this paper shows data that agrees with the notion that there is an increase in seasonal variability, but also brings in the argument that the forest as a whole is becoming drier. Thus, it seems that the dryness of the dry season outweighs the wet season. This is sure to bring some kind of change to the ecosystem in the years to come.
Sources: Espinoza Villar, J. C., Ronchail, J., Guyot, J. L., Cochonneau, G., Naziano, F., Lavado, W., De Oliveira, E., Pombosa, R. and Vauchel, P. (2009), Spatio-temporal rainfall variability in the Amazon basin countries (Brazil, Peru, Bolivia, Colombia, and Ecuador). International Journal of Climatology, 29: 1574–1594. doi: 10.1002/joc.1791

Poster!

Hi all,

I made a poster giving an overview of my blog so far, and I will be uploading it as soon as I can figure out how to.

This is what I've figured out so far. There is a link here to the poster, where you can see it up close in all its academic beauty. I've also included an image of the poster below, where it is probably hard to read but gives a general notion of what it looks like.

People vs. Forest

Historically speaking, widespread deforestation of the Amazon is fairly recent. In 1970, the Brazilian government inaugurated the Transamazon Highway, and with it kicked off the intense deforestation we see today. In an article by Fearnside, he details the history and effects of this practice. As is usually the case, the biggest motivator in clearing the forest is to make space for traditionally lucrative activities. In Brazil, the expansion of land for cattle ranching is the main enemy, but clearing the land for agriculture also plays a major role. Brazil is a major exporter of meat, and this industry is dominated by medium to large landowners, who while destroying the Rainforest are a significant contributor to the region’s and country’s GDP. The same goes for agriculture, particularly for crops like soybeans and corn.

In order to clear the land, the most common practice is to burn the desired sections of forest. Even though Amazonian soil is sandy, poor in nutrients, and overall not fit for crops, there are still attempts at using it for agriculture. What happens is that whatever is planted does not last more than a few years, and a new plot of land needs to be cleared.

The logging industry is another damaging force. Although generally illegal, the sheer size of the forest makes it very difficult to completely stop it from happening. Nowadays, constantly updated satellite images are being used to spot this type of activity. This system of detection is an improvement but still not a perfect solution, because there needs to be noticeable deforestation before the satellite can spot the activity. Nonetheless, a step in the right direction.

Sources: Fearnside, P. 2005. ―Desmatamento na Amazônia Brasileira: História, índices e conseqüências.‖ Megadiversidade 1(1): 113–23.

Beguoci, Leandro. "O tesouro escondido na selva." Veja Sept. 2009: n. pag. Veja.com. Web. 1 Apr. 2011. 

<http://veja.abril.com.br/especiais/amazonia/tesouro-escondido-na-selva-p-072.html>. 

Climate vs. People

The potential harm being done to the Amazon Rainforest by extreme climate fluctuations is only one part of the story. The areas affected by floods and droughts are home to several million people who are forced to deal with and, sometimes, simply survive the effects that too much rain, or lack thereof, has on their lives.

 The droughts in both 2005 and 2010 left “hundreds of riverside settlements cut off from the outside world”, since several tributaries to the Amazon river dried up. This same article states that the Brazilian government tried delivering aid to the hardest-hit areas, and found that the only effective means of transportation were helicopters and planes. While this means that efforts were made to help, it also means that all the people who can only be reached by aircraft were completely stranded, and also little to no means of making a living or obtaining food, water, and medicine.

In 2010, the Negro River (Rio Negro), one of the main tributaries of the Amazon River, almost dried up due to the lack of rainfall. Here is a picture of the Rio Negro when it is flowing:

Courtesy of www.creativecommons.org

             And a picture of the river in 2010, at the peak of the drought:

Link to picture

Needless to say, this kind of situation halts the economic activities related with the river. Fishing and trade via rivers is a staple of the Amazon states’ economies, and without these, a deadly blow is dealt to the livelihoods of those who depend on the river. In order to try and offset some of the hardships brought on by drought, the Brazilian government has no option but to declare a state of calamity in the Amazon regions, and spend millions of pounds in emergency aid.

            The floods seen in 2009 were no better. Whole cities nearly disappeared engulfed in water, leaving only the rooftops of houses visible. While the water is present, the inhabitants of these cities were forced to move away, and in 2009 over 400,000 people were left homeless for the duration of the floods. What makes the situation worse is that, due to the destructive power of the floods, many people did not have homes to return to, and even more had several of their possessions washed away or severely damaged. Once again, the government response was mainly to announce a state of emergency, and spend copious amounts of money on aid.

            However, one more interesting strategy taken by the government was to give lumber seized from illegal logging activities to the poorest residents of the Amazon, so that they could rebuild homes, or build their houses higher to get away from the water. This same article spoke of how the people view floods as a natural part of the Rainforest’s cycle, and they do not have a problem dealing with the regular yearly floods. In fact, they are used to having “the rains usually end like clockwork at the end of March“. The big problem is that in 2009 the floods had more volume, lasted longer, and water levels rose much faster than usual. The exacerbation of seasons seems to be the trend in recent years, and while the effects on the Amazon itself might take a while to be fully understood, there is very little doubt regarding the power of devastation it has on the people who live in or around the forest.

Sources: Rohter, Larry. "Record Drought Cripples Life Along the Amazon ." The New York Times 11 Dec. 2005: n.pag. New York Times. Web. 31 Mar. 2011. <http://www.nytimes.com/2005/12/11/international/ americas/11amazon.html>. 

BBC News. "Severe drought afflicts Brazilian Amazon." BBC News. N.p., 23 Oct. 2010. Web. 3 May 2011.

<http://www.bbc.co.uk/news/world-latin-america-11610382>. 

USA TODAY. "Amazon hit by climate chaos of floods, drought ." USATODAY.com. N.p., 25 May 2009. Web. 

3 May 2011. <http://www.usatoday.com/weather/2009-05-25-amazon-drought-and-floods_N.htm>.  

And the other extreme…

In order to complement my previous post, I have written this one to deal with the topic of extreme droughts in the Amazon Rainforest. Only a few years ago in 2005, the Amazon experienced an unusually dry season caused in part due to the 2002-2003 El Niño. The El Niño/Southern Oscillation is known to influence the climate of the forest, and as I mention in my previous post, is responsible for magnifying the effects of the flooding season as well as the drought season (I will write more about the ENSO in a future post). The difference in 2005 was that in addition to the ENSO affecting the Amazon from the Pacific Ocean, there was also a warming of the waters in the Atlantic Ocean.

The result was an “extreme drought event in the Amazon river basin, regarded as the worst in over a century”, as outlined by a paper by Chen et al. This is the same Chen from my previous post, and once again he uses GRACE satellite measurements to back his findings. There was in fact a widespread deficit in terrestrial water storage in August/September (apex of the drought) compared to the average TWS changes in the values they had for the years 2002-2007. The regions that were hit the hardest saw a decrease in 20-30 cm of water. Also, the average accumulated precipitation from June to September in 2005 was almost 150mm lower than the previous year.

What does all this mean? First of all, the Brazilian government announced a “state of public calamity” in the populated areas. Significant amounts of crops were lost, access to water was minimal if not nonexistent, and the level of forest fires greatly rose. In fact, the state of Acre noted three times as many forest fires compared to 2004. These forest fires are not only dangerous to the local population for obvious reasons, but are a major threat to the forest itself.

Chen’s paper graphed the water levels of four river gauge stations throughout the length of the Amazon River:

Figure 6. Nonseasonal daily water-level change at 4 selected river gauge stations marked in Figure 5.
Annual and semiannual variations have been removed from these time series using unweighted least
squares fit.

A multiple meter drop in water levels means that several branches of the Amazon River, both those usually intermittent and not, dry up. For the vast majority of the population in the region, the River and its branches are integral to most aspects of daily life, ranging from transport to livelihood.

The Forest itself does not do well with this degree of dryness. Some studies have argued that when the Amazon experiences an extreme drought, there is actually a “greening-up” of the canopy, as in there is an increase in foliage. This is attributed to an increase in sunlight availability, which outweighs the lack of access to water. This claim is widely disputed; for example, a paper by Phillips et al. states there was actually extensive aboveground biomass loss. In fact, there was aboveground biomass loss in most of the monitored regions, outweighing the amount of gains, as the following graph shows:

Fig. 3. Aboveground biomass change in the Amazon Basin

and contiguous lowland moist forests. The 2005 drought reversed a multidecadal biomass carbon sink across Amazonia. Symbols represent magnitude and direction of measured change and approximate location of each plot. (A) Annual aboveground biomass change before 2005. (B) Annual aboveground biomass change during the 2005 interval. (C) Difference in rates of change in aboveground biomass, 2005 versus pre-2005, for those plots monitored throughout. Grayscale shading in (A) and (B) represents proportion of area covered by forests. Colored shading in (C) indicates the intensity of the 2005 drought relative to the 1998–2004 mean as measured from space using radar-derived rainfall data [Tropical Rainfall Measuring Mission (TRMM)].

The process of greening-up does in fact follow periods of decreased rainfall. This is a normal part of the Amazonian climactic cycle, as every year there is a dry and a rainy season. Yet this greening-up only goes to a certain extent, after which the plants begin to die off. As was shown in the case of 2005, the drought pushed the forest to and beyond that point. Another potential problem that researchers fear is that, with extreme droughts and plant death, natural selection will make it so that drought-resistant plants compose more and more of the forest. This not only means a decrease in biodiversity as the drought-susceptible species would cease to exist, but also, the drought-resistant species generally capture less carbon from the atmosphere.

Finally, I would like to bring the reader’s attention to the fact that the 2005 drought, due to the convergence of abnormal temperatures from both the Atlantic and the Pacific, was considered to be a once in a century occurrence. Until it happened again in 2010, for the same reasons, and affected an area larger than the 2005 drought (large rainfall anomalies over 3 million km2 in 2010, and 1.9 million km2 in 2005). Since this happened only last year, data on its full effects are still unknown, but what is clear is that this kind of drought should not be happening this often.

Sources: Chen, J. L., C. R. Wilson, B. D. Tapley, Z. L. Yang, and G. Y. Niu (2009), 2005 drought event in the Amazon River basin as measured by GRACE and estimated by climate models, J. Geophys. Res., 114, B05404, doi:10.1029/2008JB006056. 

 Rohter, Larry. "Record Drought Cripples Life Along the Amazon ." New York Times. N.p., 11 Dec. 2005 Web. 3 May 2011. <http://www.nytimes.com/2005/12/11/international/americas/11amazon.html>. 

Amazon Forests Green-Up During 2005 Drought Scott R. Saleska, Kamel Didan, Alfredo R. Huete, and Humberto R. da Rocha Science 26 October 2007: 612.Published online 20 September 2007 [DOI:10.1126/science.1146663]

 Drought Sensitivity of the Amazon Rainforest Oliver L. Phillips, et al., Science 6 March 2009: 1344-1347. [DOI:10.1126/science.1164033]

The 2010 Amazon Drought Simon L. Lewis et al., Science 4 February 2011: Vol. 331 no. 6017 p.554 DOI:10.1126/science.1200807

 

So what’s going on?

    The Amazon Rainforest has a dry and a wet season, so the fact that there are large variations in rainfall throughout the year is a natural part of the region’s climate. However, what has been happening in recent years is that, while there are still the two seasons, they are becoming more intense. In other words, the dry season can turn into a full-on drought, and the wet season can have floods that become destructive to both the rainforest itself and the areas surrounding the forest.
    According to a paper by Chen et al. in 2009, the northern and central parts of the Amazon rainforest experienced the worst floods in over half a century, and left nearly 400,000 people homeless. The paper details the results of a study carried out over 7 years using the GRACE (Gravity Recovery and Climate Experiment) satellite. The GRACE satellite measures levels of gravity change, and in the case of this experiment the data collected allowed the researchers to calculate the terrestrial water storage of the Amazon Rainforest. They found that from 2002-2009 there was an increase in how much water was stored in the forest, culminating with the 2009 floods.

Figure 5. The evolution of yearly TWS anomalies (in cm of equivalent water thickness change) in the Amazon basin and surrounding regions during the 7 year period from August 2002 to June 2009. Yearly averages are mean TWS changes from July of the previous year through June of the current year; for example, the 2004 TWS anomalies are the mean during July 2003 through June of 2004. Seasonal (annual and semiannual) signals and the 161 day S2 alias error have been removed through unweighted least squares fit as well as the mean field for the 7 year period.

    One shocking comparison is that the surplus water stored in 2009 was “roughly equal to U.S. water consumption for a year”. Besides the effect this had on the people who were left without a home, excessive flooding can put the ecosystem at risk simply because it is not meant to withstand this kind of weather.
    This study also points to the link between extreme climate variability in the Amazonian Rainforest and El Niño/Southern Oscillation (ENSO). An exceptionally dry season in 2002-2003 is linked to El Niño, and the 2009 flood with La Niña. In fact, the paper has a great comparison between two graphs, one showing precipitation anomalies and the other showing sea surface temperature anomalies i.e. presence of El Niño/La Niña.

Figure 8. (a) Monthly precipitation anomalies for 1997–2009 in the lower Amazon basin (the area encircled by the magenta contour in Figure 3). Each monthly precipitation anomaly is computed by removing the mean monthly precipitation (for that month), estimated for 1997–2008. (b) The NINO3.4 index over the period 1997–2009. NINO3.4 is the average sea surface temperature (SST) anomaly in the region bounded by 5°N–5°S, 170°W–120°W. This region has large variability on El Niño time scales and is close to the region where changes in local sea surface temperature are important for shifting the large region of rainfall typically located in the far western Pacific. The NINO3.4 index time series is provided by the Royal Netherlands Meteorological Institute (http://www.knmi.nl).

    I think that the most important thing to take from this paper is that, while the Amazon Rainforest is by definition subject to intense weather shifts, the climactic extremes are becoming too much, even by Rainforest standards.

Sources: Myneni R.B, et al. 2007 Large seasonal swings in leaf area of Amazon rainforests. Proc. Natl Acad. Sci. USA. 104, 4820–4823. doi:10.1073/pnas.0611338104.

Chen, J. L., C. R. Wilson, and B. D. Tapley (2010), The 2009 exceptional Amazon flood and interannual terrestrial water storage change observed by GRACE, Water Resour. Res., 46, W12526, doi:10.1029/2010WR009383.

Welcome!

    The title of this blog, “Can’t Stop the Waters of March”, is a reference to the song “Waters of March” composed by Bossa Nova legend Tom Jobim. Through imagery and metaphors, the song speaks of the rainfall that accompanies seasonal change in Brazil. However, recent droughts and floods in Brazil show how this previously stable cycle is becoming more and more disrupted. In this blog, I hope to provide an interesting look at the effects of climate change on one of Brazil’s (and the world’s) greatest treasures, the Amazonian Rainforest.

   Luckily for my blog, Tom Jobim wrote lyrics to this song in both Portuguese and English, so any interested readers can take a look at what they say and not just take my word for it.
Song in English, Portuguese, and lyrics in English, Portuguese.