Projections of future meteorological drought and wet periods in the Amazon

Abstract

Future intensification of Amazon drought resulting from climate change may cause increased fire activity, tree mortality, and emissions of carbon to the atmosphere across large areas of Amazonia. To provide a basis for addressing these issues, we examine properties of recent and future meteorological droughts in the Amazon in 35 climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5). We find that the CMIP5 climate models, as a group, simulate important properties of historical meteorological droughts in the Amazon. In addition, this group of models reproduces observed relationships between Amazon precipitation and regional sea surface temperature anomalies in the tropical Pacific and the North Atlantic oceans. Assuming the Representative Concentration Pathway 8.5 scenario for future drivers of climate change, the models project increases in the frequency and geographic extent of meteorological drought in the eastern Amazon, and the opposite in the West. For the region as a whole, the CMIP5 models suggest that the area affected by mild and severe meteorological drought will nearly double and triple, respectively, by 2100. Extremes of wetness are also projected to increase after 2040. Specifically, the frequency of periods of unusual wetness and the area affected by unusual wetness are projected to increase after 2040 in the Amazon as a whole, including in locations where annual mean precipitation is projected to decrease. Our analyses suggest that continued emissions of greenhouse gases will increase the likelihood of extreme events that have been shown to alter and degrade Amazonian forests.he responses of tropical forests to severe droughts exert strong influences on the global carbon cycle (1, 2). During periods of extended soil water stress, changes in forest physiology and structure reduce the capacity of forests to cycle and store carbon (3-5). In the 2000s, for example, more than half of the Amazon experienced droughts that were severe enough to cause increased tree mortality and reduced tree growth (6). In response to these droughts, 1-2% of the carbon stocks of Amazonian forests were committed to the atmosphere (6, 7), while large amounts were combusted due to widespread fires. Although similar droughts have occurred for millennia (8), and forests have apparently recovered from such events (9), climate change could intensify hydrological extremes over the basin (10). Together with warmer climatic conditions, an increase in the frequency and severity of droughts could push the Amazon region into a new climate envelope (11), potentially releasing to the atmosphere a large part of the 120 Pg of carbon stored in these forests (12). These effects on the carbon stocks of the Amazon could be even more pronounced if forest fires become more common in the region.There is disagreement about the potential responses of Amazon forests to climate change (13). Earlier versions of climate−vegetation models projected that as climate changed, many forests growing in southeast Amazonia wo...

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“…Above a 3275 mm yr −1 precipitation threshold the production of new leaves seasonality depends almost exclusively on the incident radiation seasonality, while below a threshold of 1635 mm yr −1 the production of new leaves is only limited by precipitation. Areas where photosynthesis is driven by radiation and have a MAP close to the ≈1943 mm yr −1 threshold can potentially turn into water limited forests due to the expected increase in the frequency and intensity of extreme droughts [67]. If this climatic shift occurs, vegetation in these areas are likely to change towards a forest dominated by deciduous tree communities instead of the evergreen forests.…”

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“…Nos últimos anos tem sido observado aumento na incidência de eventos de seca na Amazônia (Baker et al, 2008;Cox et al, 2008;Brando et al, 2008), que podem ser agravados no futuro (Heil Costa et al, 2009;Duffy et al, 2015). Modelos climáticos projetam para as próximas décadas uma tendência de aumento na frequência e extensão geográfica de tais eventos de seca para a Amazônia (Duffy et al, 2015). Para toda a região amazônica, esses modelos climáticos sugerem que as áreas afetadas por secas intensas irão triplicar até 2100 (Duffy et al, 2015).…”