'Major issue in climate change': New modelling predicts the nature of extreme rainstorms in the U.S. is changing

Those are the projections based on recent high-resolution climate modelling, which was discussed in a paper published in the peer-reviewed journal Earth’s Future. 
 
“This is not only a major issue in climate change, but it’s a major issue in risk assessment in general,” said one of the study’s authors, Dr. Simon Papalexiou, assistant professor in the College of Engineering and member of the Global Institute for Water Security at the University of Saskatchewan (USask).  
 
“The 20-year event is not a very large event — it's not a catastrophic one like the one that comes on average once every 100 years — but still events that come once every 20 years can cause damages in infrastructure and crops.” 
 
Papalexiou specializes in modelling complex systems and was involved in efforts to verify the state-of-the-art Weather Research and Forecasting (WRF) model. To do this, he crunched hourly rainfall data collected from 3,119 weather stations across the United States over a 13-year period from 2000 to 2013. The projection looks ahead to the years 2071 to 2100 and assumes that greenhouse gas emissions will continue to be the same as they are today, and that the climate will continue to warm. 
 
The model’s resolution is so granular it can predict hourly precipitation within a four-kilometre radius. 
 
Papalexiou, who also leads research programs within the pan-Canadian Global Water Futures Program, said the ability to hone in on weather patterns in such small areas is more useful than broader climate predictions. 
 
“A very small area is what, really, people need to know about, isn't it?” he said. “Cities — small cities, large cities —care less about what's going to happen in a one-degree-by-one-degree region, which means 100 kilometres by 100 kilometres.” 
 
The climate model Papalexiou and co-authors worked on stands out because it was verified using hourly rainfall data, as opposed to daily numbers. Unlike daily data, hourly figures capture information about the intensity and duration of storms, which people need to understand in order to make appropriate decisions about infrastructure design.  
 
Projections suggest storms with extreme rain are going to become more frequent, more intense and go through significant changes in seasonality and duration. Taken together, that will affect ecosystems, increase flood risk and threaten societies that have adapted to certain climates. 
 
The greatest intensification of weather events is predicted to occur in the western United States, the Pacific coast, and some parts of the east coast.  
 
Storms are expected to decrease in duration on the Pacific coast, which could reduce the ability of vegetation to intercept and absorb water.  
 
The model projects that storms will happen more evenly throughout the year in the Great Plains and the northern Rockies, defying traditional seasonal trends. 
 
“In these regions there are major vast grasslands and crop production,” Papalexiou explained. “Nobody knows, if actually these changes in seasonality happen, how this will affect the crop production on these huge vast grasslands.” 
 
While Papalexiou describes the WRF model as “the best model out there,” he cautions that its predictions will come to pass only if the assumptions it’s made bear out. If the rate of greenhouse gas emissions changes — for better or for worse — that will have an effect on the model’s predictions. 
 
“We don't know what scenario will prevail. We don't know what technological advances we're going to have in reducing carbon dioxide,” he said. “There are so many factors that we don't know.” 

Full article accessible here: https://doi.org/10.1029/2020EF001824

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For more information, contact:

Mark Ferguson  
Director of Communications  
Global Institute for Water Security  
University of Saskatchewan
306-222-6915  
m.ferguson@usask.ca  

Victoria Dinh
Media Relations Specialist
University of Saskatchewan
306-966-5487
victoria.dinh@usask.ca