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How do I operate my hydro plant? In a world of water problems, there are problems that we need a good model to solve," says Colin Gleason, a hydrologist in the Riccio College of Engineering at the University of Massachusetts Amherst. But the models are only as good as the math that they're based on, and short of measuring every river in the world, there is no way to check this on a global scale.
Now, a new study led by Gleason uses data from the NASA-launched Surface Water and Ocean Topography (SWOT) satellite to determine where river estimates from state-of-the-art machine learning computer models are accurate and where they are not. "In this study, we learned where the models are right and where the models are wrong. In turn, anywhere they're wrong means their climate change predictions are wrong or their irrigation forecasts are wrong," he says.
They found that the hardest rivers to model are rivers that are dammed, rivers in arid climates (especially in highly populated areas) and Arctic rivers. While less than 10% fall into the category of "serious error," these reaches are among the most sensitive and important for water resources. This poses a challenge when one of the main uses of river modeling is to create accurate predictions for developing hydropower, planning water use (for people and agriculture) and preparing for climate change in regions with limited or no ground data.
By comparison, models are good at estimating "normal" rivers—not glacially fed, single-thread, no estuaries and no dams. "It turns out it's only 11% of the rivers on Earth that fit that definition of 'regular,' so it also kind of challenges our understanding of what a river is," Gleason said. "A weird river is the norm.
A dammed river is the norm. A multichannel, complicated planform river is the norm, not the exception." The accuracy of modeling dammed rivers has been a known issue, but this is the first time the scope of the challenge has been definitively demonstrated. Gleason explains the challenge using the Connecticut River as an example.
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