This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The historic droughts of 2023 and 2024 in the Amazon reduced river flows and altered the region's rainfall composition. Daily monitoring in Manaus, the capital of the Brazilian state of Amazonas, revealed these changes through the use of isotopes, which act as a kind of water "fingerprint." This method demonstrated how El Niño and warming in the North Atlantic affected the origin of moisture and precipitation dynamics.
Led by researchers from São Paulo State University (UNESP) in Brazil, the study suggests that isotopes can provide an early warning of prolonged droughts. The study is one of the first in more than 30 years to use isotopic techniques in Amazonian hydroclimatic research. Isotopes are lighter or heavier versions of atoms of the same chemical element.
Water molecules (H₂O) are composed of hydrogen and oxygen atoms. Most hydrogen atoms have an atomic nucleus consisting of just one proton. However, the nuclei of a small fraction are twice as heavy and consist of one proton and one neutron.
Similarly, most oxygen nuclei have eight protons and eight neutrons, though some have nine or 10 neutrons. Therefore, some water molecules are lighter and evaporate more easily, while heavier molecules condense first. "The ratios between light and heavy isotopes are altered by the evaporation and condensation of water throughout the hydrological cycle," explains Rafaela Rodrigues Gomes, a geographer and doctoral candidate at the Institute of Geosciences and Exact Sciences (IGCE) at UNESP in Rio Claro.
Gomes is the first author of a paper published in June in the journal Hydrological Processes, based on her master's thesis. Her adviser for both her master's and doctoral degrees is the coordinator of UNESP's Laboratory of Water Resources and Environmental Isotopes (LARHIA), geologist Didier Gastmans. "Each combination of temperature, humidity and other meteorological variables produces differences in isotope ratios, which can be used as a water 'fingerprint,'" Gastmans explains.
Studies on variations in rainfall isotopes in the Central Amazon began in the 1960s. These studies were primarily conducted by researchers at the Center for Nuclear Energy in Agriculture at the University of São Paulo (CENA-USP), in partnership with the International Atomic Energy Agency (IAEA). Between 1965 and 1990, monthly rainwater samples were collected in Manaus, albeit with interruptions in some years.
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