The droughts 2013/2014 in Southeast Brazil

Abstract

The claim that droughts in the Southeastern Brazil are being caused by deforestation in the Amazon has no scientific basis and does not survive an analysis of the available climate data. The severe drought that affected Southeastern in the years 2013 and 2014-and caused social adversities due to the lack of water for human consumption particularly in large cities-is due to the natural climate variability and droughts have occurred in the past, even with greater intensity, notably in the 1930s and 1960s, when the deforestation of the Amazon was incipient. The atmospheric humidity for the Southeastern rainfall is not produced in the Amazon. It comes from the Tropical Atlantic, only passes over the Amazon and interacts with the forest. Using a virtual box inscribed from 0º to 12,5ºS, 45ºW and 75ºW, the annual moisture flux divergence for the years 1999 to 2014 is calculated using the Reanalisys data set available at ESRL/PSD/NOAA. The results show that the years 2013 and 2014 presented the largest mean annual flow values exported towards Southeastern Brazil, 2014[3,45x108kg/s] and 2013[3,08x108kg/s] respectively, during the period of this study. Therefore, it is clear that the 2013-2014 severe drought was not caused by the lack of atmospheric moisture flow. In addition, the analyses of vertical velocity Omega and Outgoing Long Wave (OLR) data observed during the austral summer show the presence of a high pressure system over the Region that resulted in an abnormally atmospheric stability particularly in 2014. Though there is a strong solar heating during the summer season, this high pressure system caused the drought since it inhibited convection and development of thunderstorms as well as blocked the frontal system propagating from southern South America, that is a primary dynamic mechanism for most of the regional rainfall in the summer season. One concludes that the drought in the Southeast Region in the years 2013-2014 was not caused by a lack of atmospheric moisture, but the absence of a dynamic mechanism capable of converting into rainfall the moisture flux originating in the Tropical Atlantic.