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New Findings Unlock Climate Change Information Stored in Rain Samples

By studying oxygen and hydrogen isotopes in rain samples, IAEA scientists will be able to track different types of rain. (Photo: R. Quevenco/IAEA)

New conclusions by IAEA researchers lay the foundation for a better understanding of the effects of climate change on how it rains, which will contribute to an improved understanding of precipitation patterns.

As a warmer atmosphere can hold more moisture, the patterns of rain are expected to alter as a result of climate change. Adaptation measures require knowledge about not just whether it will rain, but also how it will rain.

Will the rain be sudden, intense and local – that is, mostly of a type that is called convective? Or will it be mostly of the stratiform type, which is lighter and falls over a larger area for a longer time? Climate change is expected to affect the mix of these two rain types, something that can wreak havoc, as intense local rains may cause more floods and draughts.

On 13 June 2016, IAEA isotope hydrology specialist Pradeep Aggarwal and several co-authors announced in a scientific paper published in Nature Geoscience (paywall) that the oxygen and hydrogen isotopes in rain samples indicate the ratio of the types of rain contained in the samples.

Isotopes are atoms of the same element that have different numbers of neutrons, resulting in different atomic weights. The ratio of heavy to light isotopes changes during the condensation and evaporation of water. Because stratiform and convective rains are formed through different processes, the isotopes contained in a rain water sample function as trackers of the types of rain it contained, according to the new findings.

Aggarwal and his colleagues came to this conclusion by studying data from a monitoring network that was created by the IAEA and the World Meteorological Organization in 1961 mainly as a tool to track radiological fallout from atmospheric nuclear bomb tests, but now is used by scientists to learn about the water cycle. Crunching the numbers from this database along with data on the two types of rain from satellite and cloud observations led them to the conclusion, which helps unlock information stored in not only the rain sample database, but also water captured millennia ago in aquifers, continental glaciers in the tropics and tree rings.

By studying the isotopic proportions contained in this water, scientists will be able to provide reliable estimates of the ratio of the two rain types, which contribute to better climate models and predictions of future precipitation changes.

"To better understand climate change, you have to understand the water cycle as it is both affected by climate change and contributes to it," Aggarwal said. "By improving our knowledge about the ratio of the two fundamental rain types, these findings contribute to our understanding of how climate change will affect rain patterns, which will enable better adaptation."

This research forms part of the IAEA’s programme of work on isotope hydrology and water resources, and it benefits IAEA Member States as they will be able to access more accurate climate models that enable them to better adapt to climate change.