In the Prairie Potholes region, spanning the southern Alberta, Saskatchewan, and Manitoba prairies, water doesn’t go straight from precipitation and snowmelt to streamflow, its first intercepted and stored by millions of small but densely located wetlands. When a wetland fills up it switches from storing to releasing water. In a system with millions of these wetlands, a sudden switch can have intense effects on downstream river conditions.  

New research from Javad Rahmani (PhD Candidate) and Dr. Ali Ameli (EOAS Assistant Professor), and collaborators at the University of Toronto and Ducks Unlimited, published in Nature Communications,  Earth & Environment, confirms that these wetlands play a central role in determining how much rain and snowmelt becomes streamflow, with implications for flood and drought preparedness and vulnerability, and the regional ecosystem’s water balance. Using 38 years of satellite-based hydrologic maps the authors show that the intercepting role of the wetlands means that the same rainfall or snowmelt event can produce very different streamflow depending on how full the wetland network already is. Small increases in wetland storage can trigger large changes in runoff if the wetlands were already pretty full, or a large rainfall can have no impacts if they were empty, but the relationship is not uniform throughout the Prairie potholes regions.  

The expanse of the region and immense number of wetlands means that modelling every wetland is impossible – the necessary information often doesn’t exist even if there was enough time and resources for millions of models. A study by Rahmani, Ameli, and coauthor Chaopeng Shen at the University of Pennsylvania published in Water Resources Research, tackles this problem: how do we predict wetland outflow behaviour where streamflow gauges and detailed wetland inventories are sparse? Rahmani and co-authors developed a physics-informed deep learning model to combine what data was available with the principles of how wetlands store, release, and connect water. Applied across catchments, the model predicted streamflow and pothole water storage more accurately and consistently than purely data-driven approaches, allowing for reliable predictions to be made in ungauged watersheds.  

This research highlights the risks involved in Alberta’s new wetland policy, which came into effect in March and exempts farmers from wetland preservation rules if the wetland is only filled seasonally based on a 17-week cutoff. This seasonal cutoff is a concern for Dr. Ameli, who argues that these seasonally dry wetlands are those with the highest buffering capacity, meaning that if you remove them, you may be increasing downstream flood risks dramatically. “A fixed 17-week cutoff ignores the fact that the same pothole that holds water for 8 weeks in a dry year may hold water for 22 weeks in a wet year,” explained Ameli, “once cultivated through in a dry year, it cannot buffer the wet year when it matters most.”