Figure 14 - Projected climate change over Brazil and the Amazon, Sao Francisco and Parana river basins by 2011-40, 2041-70 and 2071-2100 relative to 1961-1990
associated with different levels of global warming and CO2 concentrations. Direction of the changes in rainfall is indicated by arrows, and the regional
warming is also shown in the figure. Source: Marengo et al. 2011c.
3.2 Climate extreme events
Considering the extreme drought in 2005, and using a version of UK Hadley Centre global climate model, Cox et al. 2008 estimated how the probability
of a ‘2005-like’ drought year in Amazonia changes over time. It suggests that under present conditions, 2005 was an approximately a 1-in-20-year
event one drought like 2005 would be expected in a 20-year period, but may become a 1-in-2-year event by 2025 and a 9-in-10-year event by 2060.
In other words it may become the rule rather than the extreme. If severe droughts like that of 2005 do become more frequent in the future this
demands adaptation measures to avoid impacts on the population, particularly those living on the river’s bank. The impacts felt during this
drought of 2005, and again in the extreme drought in 2010 Marengo et al.,
2011b, show how local populations are vulnerable to climate extremes: local farmers are affected by drought due to high temperatures and dry
conditions; and river levels are extremely low making transportation along the main channels impossible, which in many cases is the only way for
populations to move around and remain connected. Two record extreme droughts in less than five years is something that has highlighted the
negative impacts of extremes of climate variability and climate change in the region. There is positive evidence that effective measures directed
towards climate change mitigation are needed. Examples would include the reduction of deforestation and also in the emissions of GHG, reducing
warming and thus impacts. Effective measures sought by decision-makers should also include adaptation plans to cope with the possibility of extreme
droughts and floods becoming more frequent and intense in Amazonia in the near term.
3.3 Climate change and land use change
The combination of climate change, on a long-term and large scale, and deforestation, through changing local climate patterns, might result in a
warmer and possibly drier climate in the Amazon region. The positive feedback of these processes, with possible changes in the Amazon vegetation
structure “savannization” and forest die back, is illustrated in Figure 15. In general, changes in humidity e.g. precipitation amount, frequency and
increases in temperature can cause forest decline. A key element is the ecological adaptation to the intensity and frequency of drought spells. As
observed by Choat et al 2012 the xylem embolism could represent a serious risk for forests in adapting to changes in climate. Species more resilient to
longer periods with water deficit in the soil and higher atmospheric water demand, which forces evapotranspiration, are the ones that will last longer
in drier climate conditions. This might cause change in the forest biodiversity and ecological functioning, at least until a new equilibrium is
reached.
Figure 15: Simplified potential mechanisms of Amazon ‘die-back’. CO2 is not the only greenhouse gas emitted, but is highlighted here because of its importance in
climate change, its role in the earth’s carbon budget, and effects on plant physiology relevant to the Amazon rainforest. Through feedbacks on the global
and regional climates, loss of the Amazon forest may also have implications for the climate, ecosystems and populations lying outside the Amazon basin
Marengo et al 2011d.
Forest fire is another key process acting on land cover changes, the vegetation structure, the energy balance and emissions of greenhouse gases
Figure 15. In drought conditions, fires set for forest, or even pasture, clearance burn larger areas. Anthropogenic forest fires, logging and drought
act in a positive loop on increasing forest vulnerability and susceptibility to subsequent burning while deforestation and smoke can inhibit rainfall,
exacerbating the potential for a dry climate. Smoke and reduced rainfall has a direct impact on human health and living, disrupting transport at local
and regional level, and compromising access to medicines and food as experienced during the Amazon drought of 2005 and 2010. Climate change
acting on a region already fragmented by deforestation could have larger effects than on a continuous forest.
4. Case study - Climate extreme events in Amazonia: imminent threats to human security
