Hydrology, Cryosphere & Earth Surface Research Spotlight

Rainfall Fluctuations Hinder Projections of Future Extremes

Long-period oscillations in rainfall make even long records less useful for predicting future extremes.

Source: Water Resources Research

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Scientists highly value multicentury records of weather because they can provide valuable insights into climatic changes and extremes. One station in Padua, Italy, has conducted daily observations of rainfall since 1725. Detailed data sets going back this far provide scientists a unique opportunity to better understand how climate fluctuates over time and how atmospheric and climatic cycles affect an area’s weather patterns.

However, no one had ever analyzed the Padua data set at the daily level. Marani and Zanetti performed the first analysis of this station’s data down to the individual day; despite some gaps in the record, the authors were able to study 268 full years of measurements.

Specifically, the authors document extremes in rainfall and assess how these extremes changed over time in response to atmospheric circulation patterns and climate change  The team found that annual rainfall slightly decreased over the period of study, and the number of rainy days, although fluctuating, showed no major trend. However, rainfall extremes seem to follow a very different behavior. Extremes slightly intensified and exhibited wide oscillations, partly in sync with a dominant climatic pattern known as the North Atlantic Oscillation (NAO).

The authors observed at least five distinct cyclical oscillations in the rainfall data, with cycle durations ranging from roughly 17–21 to 145–172 years. These long-term oscillations and weather patterns are likely to have affected precipitation in other regions as well. As a result, the authors conclude, past observations, especially from records lasting a century or less, cannot necessarily shed light on future climate extremes. (Water Resources Research, doi:10.1002/2014WR015885, 2015)

—Puneet Kollipara, Freelance Writer

Citation: Kollipara, P. (2015), Rainfall fluctuations hinder projections of future extremes, Eos, 96, doi:10.1029/2015EO030993. Published on 10 June 2015.

© 2015. The authors. CC BY-NC 3.0