by Vijay Jayaraj
Brazil has been in the midst of controversy for not acting on climate change. Greta Thunberg and other children have named Brazil as one of the five countries in a lawsuit for climate inaction. Brazil’s President Bolsonaro has also been under heavy fire for being skeptical towards the climate crisis movement.
The biggest news in recent times was the fires in the Amazon rainforest. 60 percent of the rainforest is situated within Brazil’s borders. Rainfall is an important component for the forests within Brazil’s borders and also for Brazil’s highly populated cities.
Proponents of Catastrophic Anthropogenic Global Warming (CAGW) insist that human greenhouse gas emissions have worsened climate change. Some of them say that the CAGW has caused an increase in extreme rainfall events like floods and droughts.
Here we shall take a look at the rainfall pattern in Brazil—both regional and national level—to determine if there are significant negative imprints of anthropogenic global warming and whether the CAGW proponents’ claims are true.
Just as with any big country, Brazil’s geography is diverse, and the rainfall patterns are different in different regions. Nevertheless, some studies analyze the national-level changes in rainfall.
Detailed research in 2014 tried analyzing the annual maximum daily rainfall trends in the Midwest, southeast, and southern Brazil for 71 years. It concluded that “there is a positive trend in the annual maximum daily rainfall data series.”
Figures: Decennial means and reference series for Midwest, Southeast, and South regions; Maximum daily rainfall for the Midwest, Southeast, and South regions
Figure Source: https://www.sciencedirect.com/science/article/pii/S2212094714000802
A 2017 study on the “Historical analysis of interannual rainfall variability and trends in south-eastern Brazil” explained that the rainfall patterns have been largely influenced by weather phenomena in the Atlantic and Pacific oceans, not by CAGW.
Rainfall patterns were highly sensitive to the coupled impact of three major ocean-atmosphere climate variabilities: the El Niño-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO).
For Southeast Brazil, the precipitation was below normal during the first cold AMO phase (1888–1930) and above normal throughout the second cold AMO phase (1964–1994). During the AMO warm phase, drought periods were extremely severe. Precipitation also seems to follow PDO index trends and El Nino years brought wetter years.
It has also been understood that the climatic changes in Northern Hemisphere such as the Little Ice Age (between approximately 1500 and 1850) and the Medieval Climate Anomaly (between 900 and 1100, also called the Medieval Warm Period), have had a influence on South American rainfall patterns, including Brazil.
The Amazon rainforest (including the 40 percent outside Brazil) has displayed a similar ENSO-influenced positive rainfall trend.
The World Bank’s climate knowledge portal says the Amazon experienced a 5 percent increase in rainfall over the past three decades, and the three most recent droughts (2005, 2010, 2015/16) were due to ENSO weather phenomenon, not CAGW.
A 2010 research report published in the Geophysical Research Letters measured the change in greenness of the Amazon using NASA MODIS satellite data. The study explicitly stated that “Amazon rain forests were remarkably unaffected in the face of once-in-a-century drought in 2005, neither dying nor thriving, contrary to a previously published report and claims by the Intergovernmental Panel on Climate Change.”
A newer study in 2015 analyzed the seasonal rainfall variations in the Northern Amazon between 1979 and 2011 and concluded that there has been a significant increase in rainfall over the Northern Amazon region.
Conclusion: It is very evident that the rainfall patterns over Brazil and the entire Amazon are sensitive to the changes in weather patterns over the ocean. However, the rainfall patterns have not been significantly disrupted or impacted by the supposed CAGW in recent decades. All major droughts in the past two decades were due to periodic ENSO weather patterns, and there has been an overall increase in Amazon rainfall levels.
Vijay Jayaraj (M.Sc., Environmental Science, University of East Anglia, England), Research Contributor for the Cornwall Alliance for the Stewardship of Creation.