FINAL REPORT - International Joint Commission

ANNEX 2
Climate Change Scenario Development
In recent IJC and U.S. Global Change Research Program studies, the Great Lakes Environmental Research
Lab (GLERL) completed modeling of hydrologic impacts of climate change for the Great Lakes region.
This work used meteorological outputs from two GCMs and transformed them into hydrological impacts
with models of rainfall/runoff, lake evaporation, connecting channel flows, lake regulation, and lake water
balances. However, climate change projections were not included in this work for the Ottawa River basin
and lower St. Lawrence River. GLERL made GCM results available over these extended areas, and
hydrologic modelers at Hydro-Québec expanded the estimation of climate change hydrological impacts
over these areas. GLERL and Hydro-Québec compared their climate change projections in preparation for
a new joint assessment of climate change impacts on hydrology over the entire Great Lakes-St. Lawrence
River basin in conjunction with the latest GCM simulations (the Canadian and U.K. Hadley GCM).
The project focused on a future 20-year window for 2050 (2040-2060). GLERL acquired GCM scenarios
for the latest versions of the Canadian and U.K. Hadley models. In order to evaluate the climate change
impact, thirty-year windows were chosen with four critical scenarios. Of these, two scenarios were from
the third generation Hadley GCM, with the other two from the second generation Canadian GCM. For the
purposes of this project, these are termed HADCM 3A representing a warm and wet climate regime,
HADCM 3B for a not so warm and wet condition. For the Canadian GCM, these are CGCM 2A for a warm
and dry regime and CGCM 2B for a not so warm and dry condition. It was noted that the term “dry”
implies conditions with less precipitation than the Hadley simulations and not necessarily less precipitation
than the current climate regime. These models were refined from the versions used in the U.S. National
Climate Change Assessment. In particular, the Hadley Centre model exhibited a better agreement between
the effects of atmospheric sulphate aerosols, as represented by the simplified parameterization that they
routinely use, and much more lengthy and precise calculations.
GLERL extracted and provided Hydro-Québec with GCM output changes between a baseline period of
1961-1990 and the future 30-year periods. These changes provided for several variables: daily
precipitation increase (ratio), minimum daily air temperature increase at 2 m (ºC), average daily air
temperature increase at 2 m (ºC), maximum daily air temperature increase at 2 m (ºC), wind speed
increase at 2 m (ratio), specific humidity increase (ratio), and cloud cover increase (ratio). GLERL
adjusted historical meteorology data for the Great Lakes basin with the GCM climate changes, while Hydro-
Québec and the Ministère de l'Environnement did the same for the Ottawa River basin. GLERL then
simulated Great Lakes hydrology under the various scenarios while Hydro-Québec and the Ministère de
l'Environnement did the same for the Ottawa River basin.
• Key Findings
• The Hadley scenarios generally increase precipitation more than the Canadian GCM scenarios.
Precipitation is greater than the base case on all lakes for the Hadley scenarios. For the Canadian
scenarios, precipitation is greater on all lakes except Michigan, St. Clair, and Erie. The largest
values are seen on Georgian Bay for the HADCM3A scenario and on Erie for HADCM3B.
• Net basin supply is generally less than the base case for all changed-climate scenarios for all lakes
except for the HADCM 3B scenario on lakes St. Clair, Erie, and Ontario. The greatest reductions in
net basin supply occur on all lakes under the CGCM 2A (warm, dry) scenario, followed by either
the CGCM 2B (less warm, dry) or HADCM 3A (warm, wet) scenarios, depending on the lake; the
smallest reductions occur on all lakes under the HADCM3B (less warm, wet) scenario.
• The higher air temperatures under the changed-climate scenarios lead to higher over-land
evapotranspiration and lower runoff to the lakes, with earlier runoff peaks since snow pack is
diminished and the snow season is greatly reduced. This also results in a reduction in available
soil moisture. Water temperatures increase and peak earlier; heat resident in the deep lakes
138 Options for Managing Lake Ontario and St. Lawrence River Water Levels and Flows