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Changes in non-extreme precipitation may have not-so-subtle consequences

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September 19, 2017 National Science Foundation

Non-extreme precipitation can have a strong effect on ecosystems, agriculture, infrastructure design and resource management, the scientists say, pointing to a need to examine precipitation in a more nuanced, multifaceted way.

“This study shows that everyday precipitation events — not just the extremes that have been the focus of most studies — are changing,”

…”It’s not just the amount of rainfall that’s important …it’s the duration of that rainfall and the amount of time between rainfall and dry periods….”Shifts in the daily patterns of rainfall, sometimes subtle, also occur. These can be very hard to document, but the existence of long-term monitoring sites provides the information needed to recognize trends and plan for the future.

…In areas such as Oregon’s Willamette Valley, the researchers observed decreases in the total annual precipitation, the number of days per year with precipitation, and the number of consecutive days with precipitation. The areas immediately surrounding the valley, however, had increases in those measures.  “Examples like this indicate that it may not be the best practice to make broad assumptions like ‘all wet areas are becoming wetter and all dry areas are becoming drier,”…

“Hydroelectric plants, storm water drainage systems — any structure that relies on an assumption of expected precipitation — could be vulnerable as we look toward becoming more climate-resilient.”  Although current models may not be able to resolve the small but steady changes observed in this study, the researchers hope their work will inform and provide validation criteria for future models and assessments.

Susana Roque-Malo, Praveen Kumar. Patterns of change in high frequency precipitation variability over North America. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-10827-8

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