Part of the Amazon rainforest may be more vulnerable to the effects of climate change than first thought, say researchers.
Findings showed that since 1979, the dry season lasted about a week longer in each decade. At the same time, the annual fire seasons have become longer. The most likely explanation for the increasingly longer dry seasons is global warming.
If the damage is severe enough, they say the loss of rainforest could cause the release of large volumes of carbon dioxide into the atmosphere, and could also disrupt plant and animal communities in one of the world’s most biodiversity-rich regions, as outlined in the Proceedings of the National Academy of Sciences (PNAS).
The team used ground-based rainfall measurements from the past three decades. Findings showed that since 1979, the dry season in southern Amazonia lasted about a week longer in each decade.
Professor Fu and her colleagues say the water stored in the forest soil at the end of each wet season is all that the trees have to last them through the dry months. The longer that lasts – regardless of how wet the wet season was – the more stressed the trees become and the more susceptible they are to forest fires.
They say the most likely explanation for the lengthening dry season in recent decades is human-caused greenhouse warming, which inhibits rainfall in two ways: It makes it harder for warm, dry air near the surface to rise and freely mix with cool, moist air above; and it blocks incursions by cold weather fronts from outside the tropics which could trigger rainfall.