May 15, 2026: ON Branch Webinar: The Ontario Hydrologic Modeling System (OHMS): High-Resolution Provincial Modelling
Date: Friday, May 15, 2026 – 12 pm ET
Title:The Ontario Hydrologic Modeling System (OHMS): High-Resolution Provincial Modelling
Speakers: Bryan Tolson and Hongren Shen
Description:
Do you build hydrologic models, need a hydrologic model or need historical hydrologic variables for your Ontario watershed? Interested in hearing about a major advance in provincial-scale hydrologic modelling or how a process-based streamflow model performs at levels that compare very well against deep learning techniques? If you answered yes to either of these questions, you should come to this talk to learn about the new Ontario Hydrologic Modelling System (OHMS) and how we used it to create the Ontario Hydrologic Atlas (OHA). OHMS is a process-based semi-distributed hydrologic model built in the Raven Hydrologic Modelling framework and implemented at high spatial resolution and covering the entire province of Ontario. The current OHMS domain discretizes the province into over 32,000 subbasins and 130,000 hydrologic response units (HRUs), and over 10,000 explicitly simulated lakes. OHMS represents key hydrologic processes, with particular emphasis on storage-release dynamics in lake- and wetland-dominated basins, as well as consideration of tile drains, thin Canadian Shield soils, and organic soils and wetlands in the Hudson Bay Lowlands. OHMS is driven by 45 years of gridded meteorological forcing from the Canadian Surface Reanalysis (CaSR) v3.1 and achieves a median KGE of 0.88 for streamflow predictions in the 31-year calibration period across 370 streamflow stations.
We will detail OHMS performance testing results, including temporal and spatial validation testing, and then describe OHA. We will discuss our upcoming OHMS model website (coming by May 15 to hydrology.uwaterloo.ca/OHMS/OHMS.html). The OHMS website will provide a portal for users to freely 1) access, map and interrogate detailed OHMS model results via RavenView and 2) download calibrated OHMS model instances anywhere in the province.
About the Speakers:
Dr. Bryan Tolson is an expert in calibration and optimization of hydrologic and water resources models. He has more than 20 years of modelling experience. He developed the Dynamically Dimensioned Search optimization algorithm and was co-developer of BasinMaker lake and river routing network delineation software. He led the development of the Ontario Lake and River Routing Product and then co-led development of the Canadian Lake and River Hydrofabric. He has been a long-time member of the Raven Hydrologic Modelling Framework software development team and co-led the development of the CaSPAr numerical weather forecast archive. He has additional research expertise in hydrologic deep learning applications as well as hydrological forecasting.
Dr. Hongren Shen is a Postdoctoral Fellow in the Department of Civil and Environmental Engineering at the University of Waterloo. His research focuses on large-sample hydrology, hydrologic model calibration, split-sample testing strategies and GIS-enabled hydrologic workflows. He is a core developer of the Ontario Lake and River Routing Product (OLRRP) and the Canadian Lake & River Hydrofabric. More broadly, his research aims to advance scalable hydrologic modeling.
