Sea surface temperature in the North Atlantic can be a predictor for up to three months prior to extreme climate events with reduced rainfall and intense drought in northeastern Brazil. This is one of the key findings of a study by researchers in Brazil, China, Australia and Germany, according to an article published in Geophysical Survey Letters.
Using a new methodology based on the concept of precipitation deficit, the study showed that in recent years the influence of the North Atlantic has become more intractable than that of the tropical Pacific, so far regarded as one of the most important factors. in the intensity of the droughts suffered by the Northeast. At the same time, atmospheric connections between the Pacific and North Atlantic have become more frequent, suggesting that interactions between tropical ocean basins have exacerbated droughts in the region in recent decades.
“The research was prompted by the severe drought that lasted from 2012 to 2015. This long period prompted us to think, from a meteorological point of view, about how tropical ocean temperatures affect the climate. The difference now is the innovative method that compares the contrasts between the Pacific and Atlantic Oceans, and the pattern of drought in northeastern Brazil. The findings can be used as a management tool for weather forecasting ahead of events with this potential,” said Lincoln Muniz Alves, a scientist at Brazil’s National Space Research Institute (INPE). ) and a co-author of the paper, Agência told FAPESP.
The 2012-15 drought in a part of the Northeast already classified as semi-arid was so intense it destroyed crops and left towns and villages without water. Other studies had already identified changes in atmospheric circulation as the main cause, suggesting an active role played by the surface temperature of the Atlantic Ocean, which was warmer than normal, and by El Niño, a climatic phenomenon with abnormally warm temperatures in the Pacific.
This El Niño was considered one of the most dramatic (after those in 1982-83 and 1997-98) and caused losses in several parts of the world. In Brazil, adverse effects included intense drought in the northeast and Amazon, a much longer dry season than usual in the north and several parts of central Brazil (northern areas of Minas Gerais and Goiás states, as well as the Federal District), and flooding in the South.
“This type of El Niño, known as ‘canonical’ because the anomalous warming occurs in the same specific part of the Pacific Ocean, has changed both in location and in intensity. At the same time, we have seen anomalous warming in the tropical Atlantic in recent decades. “Based on our multifaceted analysis, the paper provides enough evidence for forecasters to track the signs of the tropical Atlantic several months in advance. The influence of the Pacific is undeniable, but the Atlantic has more,” Alves said.
New parameters
As explained by the authors, the study used methods such as nonlinear phase coherence and generalized event synchronization analysis to understand the cause-and-effect mechanisms underlying the studied climate phenomena. To this end, the relationships between sea surface temperature variability and the standard rainfall index were interpreted as direct interactions, while those between the oceans were interpreted as indirect effects on rainfall.
The researchers used precipitation data from the Climate Prediction Center (CPC), a branch of the National Oceanic & Atmospheric Administration (NOAA-NWS) of the U.S. National Oceanic & Atmospheric Administration. They selected four regions: northeast Brazil, the center of the drought for decades; an area called Niño 3, where there was intense activity from the El Niño Southern Oscillation (ENSO); and the North and South Atlantic Oceans, areas analyzed in previous studies.
To verify consistency, they compared the results to Niño 4, an area encompassing the central equatorial Pacific and part of the South Atlantic. For each domain, they calculated the spatial mean of the variable of interest and diurnal anomalies relative to a baseline for the period 1981-2010. The rainy season was defined as January-April and the dry season as May-August.
They concluded that the North Atlantic Ocean was the main influence on precipitation deficits and the occurrence of droughts during the period analysed. The frequencies of precipitation and sea surface temperature changed after very strong El Niño and La Niña events, increasing the probability of phase coherence.
“A normal or linear pattern as seen three decades ago no longer exists,” Alves said. “Several other studies have confirmed our results. Our methodology shows that there is no linear pattern as a basis for predictions and that conventional approaches must be abandoned. We emphasized the importance of looking at other oceans rather than just the Pacific. to watch the ocean.”
The article also concludes that other factors, such as land use change, can lead to changes in the hydrological cycle, as has already been shown by pilot studies, especially with regard to the Amazon basin. For this reason, the scientists suggest that further research using the methodology they developed should examine how land use changes alter climate characteristics and interactions.
“When we talk about climate change, we are also talking about socio-economic impacts and the impact on biodiversity. Meteorological centers can use the model to work on prevention as a contribution to public policy and decision-making about mitigating extremes. events,” Alves said.
More information:
Y. Mao et al, Phase coherence between surrounding oceans improves precipitation deficits in Northeastern Brazil, Geophysical Survey Letters (2022). DOI: 10.1029/2021GL097647