Extreme Rainfall Has Been Linked With Low Birth Weight in Babies

Extreme Rainfall Has Been Linked With Low Birth Weight in Babies
A Dessana indigenous man plays with a baby by the Negro River at the Tupe Reservation in the outskirts of Manaus, Amazonas, Brazil. (Photo: Raphael Alves, Getty Images)

Increasing extreme weather events is wreaking havoc across the globe, and may be harming the health of newborn babies in some of the world’s most remote and vulnerable populations. New research published Monday in Nature Sustainability finds a strong link between extreme rainfall events in the Amazon, which have been supercharged by climate change, and worrisome risks to babies like low birth weight and shortened pregnancies.

The study’s authors worked with a trove of more than 291,000 digitised birth registrations between 2006 and 2017 from Amazonas, a state in Brazil that is almost entirely within the Amazon rainforest. The data included births from a swath of different socioeconomic groups in 43 different municipalities located along rivers. (The researchers excluded major cities from their sample, but did include births in both rural and urban areas.)

These birth registrations didn’t just mark a baby being born: they also included the weight of the infant as well as valuable information on the mother’s age, location, marital status, whether or not they were a member of an Indigenous group, and how much formal education they had received. Using the dates of birth provided, researchers were able to retroactively map the mother’s pregnancy and tie it to any extreme rainfall events during that time period.

The research found a definitive link between extreme rainfall and worrisome effects on babies, like lower-than-average birth weight, premature births, and restricted fetal growth. Babies whose mothers experienced extreme rainfall events while pregnant had a birth weight almost 200 grams lower than average. That might not sound like a lot, but it is “very, very significant” for infants, said Luke Parry, one of the study’s authors.

“If you weigh less than 2.5 kilos, that’s been associated with a lot of developmental consequences later in life,” Parry said. Even non-extreme rainfall events, the research found, also correlated with lower birth weight: Babies had a 40% higher chance of being born underweight if their mothers were exposed to any form of increased rainfall event during pregnancy. The study wasn’t designed to explain why, exactly, this is happening, and didn’t pinpoint a specific scientific link between low birth weight and river flooding.

“It’s quite hard to separate the effects of different mechanisms because they all tend to occur at the same time,” Parry said, mentioning that more research is needed in this region and others. But he noted that the increase of infectious diseases like malaria or cholera, food insecurity, and serious emotional stress can all come with extreme rainfall and related flash floods in poorer, river-reliant communities in the Amazon. The research also looked at how higher income could change birth outcomes, finding a stark difference in birth weight between the most advantaged mothers in the sample and the least advantaged.

“Even without prenatal exposure to the extreme [weather], if a baby is born to an adolescent Indigenous unmarried mother with no formal education or natal care, the average birth weight is 648 grams lower on average,” Parry said. These extreme rainfall events, he said, are just “amplifying existing disadvantages” for the poorest populations in Brazil.

Climate change is causing “large-scale disruption to these communities,” Parry said. Recent research has shown there’s been a fivefold increase in flooding in the region. While some of it has been driven by natural cycles like El Niño, climate change is also increasing the likelihood of heavy downpours around the world due to the simple fact that a warmer atmosphere can hold more water. Despite this, Parry said, there’s been relatively little research on how the lives and health of those actually living in the Amazon are being impacted.

“These remote populations are often outside the political consciousness of the rest of Brazilian society and policymakers,” Parry said. “There’s so much physical research on the effects of climate change in the Amazon…but the actual Amazonians who have contributed very little to climate change are the hardest-hit and are basically forgotten about.”