Understand the causes of extreme drought in the Amazon – 10/18/2023 – Environment

Death of dolphins, isolation of communities, lack of water, difficulties with transportation, uncontrolled fires, interruption in energy production and health problems. The consequences of the extreme drought that has hit the Amazon in recent weeks, especially the state of Amazonas, are diverse — as are the factors that cause this climate phenomenon.

Regions of the state this year recorded the lowest rainfall in the period from July to September in the last 40 years, according to data from Cemaden (Natural Disaster Monitoring and Alerts Center), linked to the Ministry of Science, Technology and Innovation.

It is possible to point out three main agents causing this water crisis: El Niño, high temperatures in the North Atlantic and global warming caused by greenhouse gas emissions. Furthermore, the degradation of the Amazon also affects the generation of moisture in the forest.

El Niño is a natural climatological phenomenon, characterized by above-average warming in Pacific waters near the Equator. It affects the entire world, with changes in the direction of winds and the distribution of rain and heat.

El Niño, whose effects this season were noticed on the planet in June this year, changes the circulation of the trade winds, which go from east to west, taking humidity and warmer waters from the coast of the Americas to Asia and Oceania. It is also associated with global temperature records.

In Brazil, it causes increased precipitation in the South and drought in the North. “In general terms, moisture is transported by winds, especially in the southern region of South America. With more water vapor in the atmosphere, there is more rain in the southern region of Brazil and, consequently, less rain in the north of the country”, says Regina Alvalá, deputy director of Cemaden.

This year, in the Amazon region, the dry season is drier and longer than normal. This is what causes, for example, rivers to reach such low levels, as the delay in the arrival of rain prevents them from recovering at a normal rate — and, thus, they continue to dry out when they should already be filling.

This adds to another aspect, which also has to do with the ocean. The Atlantic is much warmer above the equator than below. As warmer water evaporates in greater volume, warming in the north causes more rain in this hemisphere, causing there to be less precipitation in the south.

“The planet’s water is in balance”, explains Marcelo Seluchi, general coordinator of Operations and Modeling at Cemaden. “A [quantia de] Humidity is always the same on the planet, it’s just that it is distributed. So, when there’s moisture in one spot, it means there’s a shortage in another.”

Around 97% of the planet’s water is in the oceans, according to the United States National Oceanic and Atmospheric Administration (Noaa). The small fraction that remains is distributed in glaciers, soil and the atmosphere.

Paulo Artaxo, professor at the Physics Institute at USP and member of the IPCC (Intergovernmental Panel on Climate Change), linked to the UN (United Nations), highlights that climate change also impacts the drought in the Amazon.

“The increase in global temperature also increases the temperature in the Pacific and the intensity of El Niño”, he states. “We have a particularly strong El Niño, intensified by climate change, coupled with global warming and extreme weather events.”

Artaxo explains that it is possible to say that this extreme drought is also a product of climate change even without specific studies on the current case of Amazonas, because it coincides exactly with what was predicted for the region in the face of a planet that is already 1.2 °C warmer.

“In the last three IPCC reports, the set of climate models shows that the future of the Amazon will be one of a very significant increase in temperature and a significant reduction in precipitation — regardless of El Niño and extreme weather events. But these factors do not they are completely independent of each other”, he says.

“We’ve known about this for about a decade, but now it’s happening. Now we’re observing what climate models predicted 10 years ago — and this will have a huge socioeconomic impact on Brazil,” he stresses.

Added to this is the impact of advancing deforestation and forest degradation in the Amazon. As the Amazon rainforest generates approximately half of its own rainfall through evapotranspiration from trees, the decrease in forest cover and worsening forest health result in less rainfall.

“The evaporation of vegetation is a very important input for rain, because moisture is needed to rain,” says Seluchi. “So a vicious circle is established: the vegetation is degraded because it doesn’t rain, and this degraded vegetation doesn’t evaporate and, therefore, makes rain difficult. It doesn’t rain because it’s dry, and it’s dry because it doesn’t rain.”

In November and December the rainy season begins in the North, but an analysis by Cemaden indicates that the crisis could intensify in the coming months, when El Niño is expected to reach its maximum intensity.

The agency’s forecast is that the last quarter of 2023 (which is on track to be the hottest year in history) will have below-average precipitation in most of Brazil, with the most acute situation expected to occur in the North and Northeast.

The exception is the South region, which should have more rain than normal during the period.