Section 3: Environmental and Climate Change Considerations

3.1 What is the relationship between climate change and flooding? 

Scientists know that the severity of weather extremes, such as floods and droughts, is predicted to increase. Despite considerable uncertainty as to the future impacts of climate change, the study will use the best available science to factor what is currently known into decisions regarding proposed measures. 

3.2 Why is the study assessing climate change? 

The impact of climate change on flooding is uncertain and may be the most important issue examined in the study.  If the 2011 flood was an outlier in terms of severity compared to historical floods, then the regional risk of flooding is significantly less than if the 2011 event was an indicator of the severity of floods that may occur in the future because of climate change. 

3.3 How is the study assessing climate change? 

Will future floods be higher and more frequent?  The answer for lake flooding is not as simple as for river flooding.  Higher temperatures can increase evaporation from the lake surface and may lead to lower water levels in future. However, higher precipitation in the spring increases the chance of flooding.  No climate model will eliminate uncertainty over whether future changes in evaporation or precipitation will predominate, so the study is using an approach called “decision scaling” that starts by asking what damages occur when one or the other predominates.  For instance, if future floods are much greater than historical ones, development outside the current floodplain (designed under the assumption that flooding was not likely) will be flooded.  Alternatively, if greater evaporation reduces flooding, structural measures designed to reduce water levels might prove to be an unnecessary investment.  

The study will consider a wide range of climate prediction approaches to determine how plausible those extreme outcomes are, and then will consider whether it makes sense to do something that could mitigate these worst-case scenarios even though we are not certain they will occur. 

3.4 Are floods of the magnitude of the 2011 event the new normal? 

Flooding of the same magnitude as 2011 could happen again in any given year.  Research on climate change in the basin suggests that we can expect warmer temperatures and a lower net basin water supply over time. However, even though there may be less water in the basin averaged out over the year, because of a changing climate, more frequent extreme events are expected. Research also points towards a shift in the timing of events that can lead to flooding, such as earlier and faster spring snowmelts and earlier spring rainfall. Although there is still much uncertainty surrounding the level of risk of another 2011 flooding event occurring in the basin, the potential remains. 

3.5 Is the study looking at solutions to algal blooms and other water quality issues? 

Water quality is not within the scope of this study, however the IJC recognizes that water quality is a major public concern. There was a separate study to review issues related to nutrient loading, including algal blooms in Lake Champlain, Missisquoi Bay and Lake Memphremagog as requested by the Canadian and US governments. This water quality study was completed in April 2020. Information on this project can be found on the IJC website

3.6 Is there a connection between flooding and water quality? 

Flooding affects the concentration and speed of nutrients (such as phosphorus) and contaminants, entering or moving through a lake or river and across riparian areas. Water quality can be impacted when crops and urban areas are flooded. 

Additionally, concentrations of a particular nutrient can increase or decrease depending on the volume of water available in the system, in addition to other factors, such as temperature and seasonality. 

Many of the projects being carried out under the LCRR flooding study will generate new data and knowledge about the hydraulics and hydrology of the Lake Champlain-Richelieu River system and the various uses of water. Though not central to its mandate, the study group is working closely with the IJC to share useful information related to water quality issues.