In the wake of Hurricane Harvey and Hurricane Irma, a lot of attention has been given to extreme rainfall and weather events as signs that climate change is real. But what many people haven’t been paying attention to are the changes in non-extreme precipitation events.

A team of researchers from the National Science Foundation analyzed more than 50 years’ worth of precipitation data from across North America. When they did so, they found that changes in non-extreme precipitation are more significant than previously realized—and the changes are greater than those that occurred with extreme precipitation.


Non-extreme precipitation can affect ecosystems, agriculture, infrastructure design, and resource management.

“This study shows that everyday precipitation events—not just the extremes that have been the focus of most studies—are changing,” said University of Illinois scientists Praveen Kumar, principal investigator on the NSF’s Intensively Managed Landscapes Critical Zone Observatory. “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.”

The researchers used data from more than 3,000 weather stations. In doing so, they identified several regions where the microclimate appears to have a serious effect on precipitation trends.

“This study confirms that there is more to climate than the number and size of extreme events,” said Richard Yuretich, CZO program director at NSF. “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.”

One area the researchers studied was the Willamette Valley in Oregon. They observed decreases in total annual precipitation, the number of days per year with precipitation, and the number of consecutive days with precipitation in order to track changes in non-extreme precipitation. Interestingly, the areas surrounding the valley had increases in those measures.

“Successive generations of ecosystems evolve through adaptation to these kinds of changes,” said Kumar. “If the rate of change, however small, exceeds the adaptive capacity, these environments will be susceptible to collapse.”

Researcher Susana Roque-Malo said, “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.”

Have you experienced changes in non-extreme precipitation in your area? In the bigger picture, have you noticed any changes in the ecosystem where you live? Please share your thoughts and observations in the comments.