Abstract
Previous work suggests that changes in seasonality could lead to a 70% reduction in the extent of the Amazon rainforest. The primary cause of the dieback of the rainforest is a lengthening of the dry season due to a weakening of the large-scale tropical circulation. Here we examine these changes in the seasonal cycle. Under present day conditions the Amazon climate is characterized by a zonal separation of the dominance of the annual and semi-annual seasonal cycles. This behavior is strongly modified under greenhouse warming conditions, with the annual cycle becoming dominant throughout the Amazon basin, increasing differences between the dry and wet seasons. In particular, there are substantial changes in the annual cycle of temperature due to the increase in the temperature of the warmest month, but the lengthening of the dry season is believed to be particularly important for vegetation-climate feedbacks. Harmonic analysis performed to regional climate model simulations yields results that differ from the global climate model that it is forced from, with the regional model being more sensitive to changes in the seasonal cycle.
Highlights
The Amazon’s climate, including its seasonal cycle, is strongly dependent on the interchange of water between the troposphere and the underlying surface
In order to investigate the relationship between greenhouse gas forcing and the Amazons seasonal cycle, two model simulations were performed with the Regional Climate Model (RCM) from the Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) MM5 (v3.6) model coupled to the Noah land surface scheme [20,21] and the Potential Vegetation Model (PVM) of Oyama and Nobre [10], one for present day and one for future climate
We analyze the regional distribution of near surface air temperature (t2m) and precipitation annual and semi-annual cycles using harmonic analysis, by comparing the modern climate with future climate according to the A2 scenario
Summary
The Amazon’s climate, including its seasonal cycle, is strongly dependent on the interchange of water between the troposphere and the underlying surface. As previously discussed in the literature (e.g., [1]), the driving force for this interchange is the water vapor pressure gradient between the evaporating surface and the overlying air. This complex interaction within the Amazon basin is linked to the thermal and dynamical behavior of the troposphere induced by Sea Surface Temperature (SST) variations in the Pacific and Atlantic Oceans [2,3] which are greatly impacted by the El Niño. The regional modeling study of Cook and Vizy ([7], hereafter CV08), projects a 70% reduction in the extent of the Amazon rainforest by the end of the 21st century. It should be Climate 2016, 4, 3; doi:10.3390/cli4010003 www.mdpi.com/journal/climate
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