Hydroclimatic Atlas of Southern Quebec – Key facts

Forecast of main hydrological trends

During the 21^st century, climate change will modify the flow regime of watercourses in southern Quebec and increase the risk of flooding, in addition to exerting additional pressure on the balance of water uses.

Floods

1. Spring freshet volumes will vary by region, becoming stronger in the north and weaker in southern Quebec

Due to climate change, spring flood volumes will be higher north of the St. Lawrence Valley and lower in extreme southern Quebec, but the trend remains uncertain for many rivers.

Direction of change in Annual maximum of 14-day average flow with a 2-year return period (Q14MAX2HP) – Horizons 2080, scenario RCP4.5 relative to the historical period 1981-2010.

Blue: increase
Red and orange: decrease
White: no change

2. Spring flood peaks will vary by region, becoming stronger in the north and weaker in southern Quebec

The peaks of the spring floods will be stronger in the north (around +5%), but this is highly variable depending on horizons, scenarios and regions.

Further south in southern Quebec, there is a lack of consensus on the signal, except for the 2080 horizon for the RCP 8.5 scenario, where a probable decrease of -9% is expected in certain regions.

It is advisable to consult the maps of the Atlas to note the regional disparities of these indicators. The results also vary according to the selected recurrence (Q1MAX2HP, Q1MAX20HP, Q1MAX100HP, etc.).

3. Summer and fall flood peaks will be higher over a large portion of southern Quebec

Due to climate change, extreme precipitation events are expected to worsen in terms of frequency and intensity during the summer-autumn period.

Thus, a probable increase in summer and fall floods is projected for all regions of southern Quebec.

Magnitude of relative change (%) in Summer-autumn maximum of the daily flow with a 20-year return period (Q1MAX20EA) – Horizons 2080, RCP 8.5. scenario.

4. Spring high flow will come earlier

Spring flood peaks will be one to two weeks earlier by mid-century and two to three weeks earlier by the end of the century. This trend is projected across southern Quebec.

Advancement of the Average day of occurrence of the Winter-spring maximum daily flow (JQ1MAXHP) – Horizon 2080, scenario RCP 8.5.

Red: advancement of more than 24 days.
Orange: 14 to 24 days earlier than historical normal (1981-2010)

Low flows

1. Summer low flow will be more severe and last longer

The summer season is expected to become increasingly hot and dry due to climate change.

Summer low flow will thus be more severe and longer in summer throughout southern Quebec, with drops of -15% to -25% forecast for the middle of the century and possibly reaching -43% at the end of the century.

Magnitude of relative change (%) in Summer-autumn minimum of the 7-day mean flow with a 2-year return period (Q7MIN2EA) – Horizon 2080, scenario RCP 8.5.

2. Winter low flow will be less severe

In the case of the winter-spring season, the projections describe a very probable increase in low flows for all of southern Quebec. That is to say that the low flows during the winter will be less severe.

This is due in particular to the warming of winters as well as an increase in rainfall during this season.

Magnitude of relative change (%) in Winter-spring minimum of the 7-day mean flow with a 2-year return period (Q7MIN2HP) – Horizon 2080, RCP 8.5 scenario.

Mean flows

1. The hydraulicity will vary according to the seasons and according to the regions, but it will be higher overall

The annual mean will generally be stronger, but with marked differences between seasons. Winter runoff will be higher (from +5% to +20%), while summer runoff will be lower (from -4% to -16%).

It is advisable to consult the maps of the Atlas to note the regional disparities of these indicators.

Magnitude of relative change (%) in Annual mean flow (QMOYAN) – Horizon 2080, RCP 8.5 scenario.