Development of Ontario Climate Divisions

Funded by The Great Lakes Observing System (GLOS)

Project Summary

GLISA’s Great Lakes Climatologies offer climate summaries by location (stations in US and Canada) and climate division (multi-county scale – originally US only) and have become a valuable resource for climate adaptation work across the region. In 2022, GLISA’s online climate division climatologies were expanded to include portions of Ontario as part of our Great Lakes Adaptation Data Suite (GLADS). We convened a working group of Canadian partners to develop the spatial boundaries for climate divisions in Ontario, with a focus on Conservation Authorities, to better serve stakeholders in Ontario. The new boundaries are available as a shapefile download, and future projections for temperature and precipitation change for each US and Ontario climate division are now available in GLADS and in GLISA’s online climate division climatologies (coming soon!).

Project Accomplishments & Downloads

Map of Ontario Climate Divisions (click to enlarge)

GLISA Contribution

GLISA was the grantee for this project through funding from The Great Lakes Observing System (GLOS). GLISA coordinated the working group of Ontario partners, led discussions with our partners, and synthesized working group ideas to create climate divisions for Ontario.

Project Partners

Federal Partners

  • Environment and Climate Change Canada
  • Natural Resource Canada
  • Ministry of the Environment, Conservation and Parks
  • NOAA’s National Center for Environmental Information

Conservation Authority Partners

  • Conservation Ontario
  • Central Lake Ontario Conservation Authority
  • Credit Valley Conservation
  • Essex Region Conservation Authority
  • Grand River Conservation Authority
  • Ganaraska Region Conservation Authority
  • Lake Simcoe Region Conservation Authority
  • Maitland Valley Conservation Authority
  • South Nation Conservation Authority
  • Toronto and Region Conservation Authority

Private Sector Partners

  • Aquanty
  • City of St John’s
  • Climate Risk Institute
  • Ouranos

Development of Ontario Climate Divisions

Ever since GLISA released their online climate division climatologies for the US portion of the Great Lakes region, there has been a strong interest from regional stakeholders and our partners to produce something similar over the border into Canada. Such a resource would serve all of GLISA’s stakeholders across the entire Great Lakes region. However, three major barriers existed making the task of expanding our climatologies into Canada challenging:

  1. Canada does not have official climate divisions like what are used in the U.S.;
  2. Most observational cimate stations in Canada do not meet GLISA’s data quality assurance and quality control standards;
  3. There is no standard spatially continuous observational data set available that meets GLISA’s standards and could be aggregated to the climate division scale.

In 2020, GLISA convened a group of Canadian partners to start the conversation around developing a set of climate divisions for Canada. A kick-off call was held in March of 2020 and participants supported the idea saying climate divisions would be helpful for regional adaptation applications and would scale up work that currently is done at the model grid cell or municipality scale. Afterwards, additional meetings and a series of surveys were used to move the project forward. The number and representation of stakeholders grew over the project life span of a year and a half.

A few key decisions were made by the project team that guided climate division development plans:

  1. The US climate divisions are primarily based on the aggregation of counties across each state, and Canadian divisions should be closely equivalent in size to the US divisions.
  2. Climate divisions would be developed for southern Ontario, the area GLISA serves.
  3. A target stakeholder audience would need to be identified and the spatial extent of divisions should be tailored to that group for maximum usability.
  4. Conservation Authorities (CAs) were selected as the primary audience. CAs are watershed-based, spatially cover most of southern Ontario, and project partners working in CAs saw a need for climate information summarized at this spatial scale.

Map of Conservation Authorities   Source: International Joint Commission

The project team outlined scientific priorities for how to think about developing the divisions:

  1. Climate division boundaries should be developed so that they do not need to change over time, especially in a changing climate.
  2. Lake-effect areas are important to distinguish.
  3. Elevation and distance from the Great Lakes are important considerations.
  4. Snow cover characteristics are important, especially for their impact on hydrology, but may change in the future.

GLISA started with maps of the CAs, watersheds, temperature and precipitation climatologies, and snow cover to develop an initially proposed set of climate divisions based on the project team’s scientific priorities. If neighboring CAs were in a similar climate and hydrologic regime they were aggregated to form a climate division. Aside from the Great Lakes, two main geographical features, the Niagara Escarpment and the Oak Ridges Moraine, acted as natural boundaries for the climate divisions, too. After GLISA presented the project team with an initial idea of what the climate divisions could look like, the group provided feedback about where alterations should be made based on local knowledge of geographic features, climate patterns (including lake-effects), hydrology, as well as considerations such as keeping major municipalities within one climate division if they exist in more than one CA. At times the project team held varying positions on which CAs should be aggregated together to form a division, so we tried to give partners working in nearby CAs the most weight in making decisions about those divisions. Ultimately, the project team came to agreement and the final set of divisions presented here (map below). The divisions do not specifically isolate the lake-effect zones, because in many places lake-effects are highly localized at the coastline. We do include a description of lake-effect considerations for relevant divisions within the division’s climatology page on GLISA’s website



GLISA Contact

Laura Briley, Climatologist,

Omar Gates, Climatologist,