El Niño, climate change and deforestation: scientists explain what may lie behind the drought in the Amazon

Brazil’s North region is experiencing the worst drought of the century, with severe social and economic impacts. The problem was discussed at an event hosted by FAPESP on October 17.

By Julia Moióli | Agência FAPESP – Drought has reached critical levels in the Brazilian Amazon, where the states of Acre, Amapá, Amazonas and Pará had less rainfall between July and September than at any time since 1980, and the water level in the Negro River was the lowest since 1902. The worst drought in 100 years is due mainly to El Niño, but there are also signs that climate change is responsible, according to experts who took part in a webinar on “Extreme Climate Events in an El Niño Year”, held by FAPESP on October 17.

El Niño is a phenomenon that involves unusually warm temperatures in the equatorial Pacific Ocean, contributing to changing patterns of wind and rainfall in several parts of the planet. In Brazil, it makes frontal systems (combinations of weather fronts) more frequent and persistent in the South, where rainfall increases while decreasing in the North and Northeast. 

“In El Niño years, rainfall is usually below-average in the Amazon region – not just in the state of Amazonas but also in other states of the North, as well as in the Northeast of Brazil,” said Regina Alvalá, Director of the National Disaster Surveillance and Early Warning Center (CEMADEN). “This year, moreover, the effects of El Niño are combined with those of the situation in the northern tropical Atlantic, such as more rainfall above the equator and even less rainfall in the Amazon. More research is needed to discover the extent to which the drought is due to climate change. Rainfall levels must be monitored month by month. This will also help devise a strategy to mitigate its impact.”

Regina Rodrigues, a professor at the Federal University of Santa Catarina (UFSC), highlighted a recent study estimating that gross domestic product (GDP) lost some USD 5 trillion per year for five years to the effects of El Niño in 1982-83 and 1997-98.

“This year’s El Niño appears to be equally devastating," she said. “It’s very important to stress that although the phenomenon is natural and part of the climate system, its frequency and intensity are altered by climate change due to human activity. Research shows each occurrence of El Niño will cause more damage than the one before.”

According to Gilvan Sampaio, General Coordinator for Earth Sciences at the National Space Research Institute (INPE), there is a clear tendency for extreme events to become increasingly frequent and intense. “Studies indicate that we’ll be living in a semi-permanent El Niño climate by the end of the century," he said.

“Studies show that atmospheric warming is spreading from the tropics to the middle latitudes and affecting the rainfall regime,” added Tércio Ambrizzi, Coordinator of the Climate Studies Group at the University of São Paulo's Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG-USP).

Deforestation in the Amazon makes the drought still worse by reducing evapotranspiration (loss of water from plants and the soil) and hence rainfall. Other points raised by the experts who took part in the webinar were that the dry season in the Amazon, which used to last from November through March, now lasts from October through April, that rainfall is excessive in the South, especially in Rio Grande do Sul and Santa Catarina, and that temperatures are above average practically everywhere in Brazil.

Social and economic impacts

The inhabitants of the Amazon are hard hit by the drought. River dwellers are isolated as water levels fall; dolphins and fish die as the water temperature rises; the electricity supply becomes unstable; and smoke from forest fires makes the air unbreathable in the cities. 

The economic consequences may last years and worsen as time passes, but some problems are already acute: more than 80% of agricultural areas in 79 municipalities in the North region were affected in September, according CEMADEN, and navigation is increasingly difficult as the rivers dry up, making life hard in a region where so many depend on river transportation for goods of almost every kind, Alvalá noted.

Factories in Manaus are not receiving the components they need to keep production going and distribute products to the rest of the country. “No one can guarantee that rainfall will return to normal levels, so we must manage the crisis imposed by the drought in order to mitigate its impact. We need more firefighting crews, and we also need more environmental police to prevent burning, reduce the air pollution that harms people’s health, and reduce demand for some of the materials required by healthcare professionals,” she said.

This kind of action may seem trivial, but the Amazon is a vast region, spanning an area of more than 3 million square kilometers, so coordinated action involving many bodies and actors is required, and in this sense, Alvalá highlighted the federal government’s efforts, including regular meetings to monitor the drought in the North. 

Planning is also fundamental. “We have very clear knowledge of the impact of weather events and El Niño. We can prepare three to six months in advance, especially in the case of civil defense,” Ambrizzi said.

The scientists stressed the importance of strategies focusing on urban planning, with more efficient master plans that help local communities live in the drier climate expected for the years ahead.

Sampaio noted the likelihood of changes to the crops grown in the region, for example. “Corn and dry beans require large amounts of water. Farmers in the Northeast will probably have to switch to other crops,” he said.

Knowledge diffusion

Organized by the FAPESP Research Program on Global Climate Change (RPGCC), the webinar analyzed the intensification of extreme climate events in recent decades and their association with recurring weather patterns such as those caused by El Niño. It was introduced by Maria de Fátima Andrade, a member of RPGCC’s steering committee, chaired by Ambrizzi, and live-streamed on Agência FAPESP’s YouTube channel. 

Ricardo Trindade, a professor of geophysics at IAG-USP, stressed RPGCC’s strategic importance in the 15 years since its inception. The program’s remit, he explained, is to understand how climate change happens, how its adverse effects can be mitigated, and how it is influenced by human activities.

Other speakers included Renata Tedeschi Coutinho, a researcher at the Vale Technological Institute, and Marcelo Romero, a professor at USP’s School of Architecture and Urbanism (FAU) and a member of the City of São Paulo's Climate Change Committee.

Extreme weather events and their impact on Brazilian cities

Gilvan Sampaio, who has authored several books about climate change, and Renata Coutinho, who has studied the influence of El Niño and La Niña on rainfall and extreme weather events in South America since 2002, spoke about recent research on El Niño's role in contemporary weather patterns, noting that this is a “super El Niño” year, with anomalous sea surface temperature rises of 2 °C or more. 

Romero then addressed the subject of mitigation measures and responses to extreme weather events in cities. “Cities are where most of the world population choose to live, and the trend is increasing,” he said, drawing attention to two reports issued by the United Nations Environment Program (UNEP), on climate trends and mitigation measures such as more use of renewable energy in industry, transportation and buildings, and on adaptation to climate change, especially in cities. Considering that the Paris Agreement is unlikely to be fully implemented, he advocated what he called cross-cutting measures, which combine mitigation and adaptation, citing the example of green area planting, river restoration, and urban farming.

Alvalá's presentation focused on the impact of the recent extreme weather events associated with El Niño. The numbers were alarming. “Rainfall in 103 cities in Rio Grande do Sul amounted to some 300 mm between September 1 and 4, or twice the average for the entire month,” she said. CEMADEN issued 172 warnings in September, 75% referring to cities in the South region, and recorded 194 extreme events, 87% of which were floods and landslides.

Alvalá also spoke about the ongoing drought and the risks for family farming, including socioeconomic vulnerability, which is most acute in the Northeast and also significant in the North, albeit less so in the South. Finally, she offered information about energy volumes stored in the various reservoir systems (less in the North and Northeast, more in the South and Southeast), and fire hazards, with more than 340 municipalities on high alert.

A recording of the webinar on “Extreme Climate Events in an El Niño Year” can be watched at: https://www.youtube.com/watch?v=_1ddjHDQhNk.