Rainfall associated with the Intertropical Convergence Zone (ITCZ), the belt of converging trade winds and rising air that encircles the Earth near the Equator, affects the food and water security of approximately 1 billion people worldwide. They include about 11% of the Brazilian population, concentrated in four states of the Northeast region—Rio Grande do Norte, Ceará, Piauí, and Maranhão. Large swaths of these states have a semi-arid climate, and about half of all their annual rainfall occurs in only two months (March and April), when the tropical rain belt reaches its southernmost position, over the north of the Northeast region. During the rest of the year, the tropical rain belt shifts further north. For example, it is responsible for peak rainfall in the coastal region of Venezuela in July and August.
Projecting the future behavior of precipitation in semi-arid areas like these is fundamental for society to be able to anticipate possible shifts in rainfall patterns due to ongoing climate change. A study by Cristiano Chiessi, a professor at the University of São Paulo (USP) in Brazil, and collaborators shows that precipitation in the north of Brazil's Northeast region has systematically decreased in the last 5,000 years, contrary to an important paradigm in paleoclimatology. This revised view of what happened in the past helps produce a more realistic scenario for what may happen in the future.
An article on the study is published in Paleoceanography and Paleoclimatology. The study was supported by FAPESP.
"According to the prevailing paradigm, the tropical rain belt has migrated southward in the last 5,000 years. Our research suggests instead that its latitudinal oscillation range contracted, so that it now oscillates within a narrower band," Chiessi told Agência FAPESP.
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