Canadians are feeling the effects of climate change to a greater degree and facing more serious consequences than federal scientists projected less than a decade ago.
That’s the message in a comprehensive federal report released earlier this month. It details how climate change is physically transforming the country and how those trends are likely to become more pronounced in the future, from floods, wildfires and heat waves to vanishing glaciers and permafrost.
CHAPTER ON CHANGES IN THE WATER CYCLE
The fifth chapter of the report, “Changes in the Water Cycle” assesses past and future climate-related changes in components of the water cycle that impact freshwater availability in Canada, namely, the atmospheric component of the water cycle (evaporation and precipitation), streamflow, surface water storage (lakes and wetlands), groundwater, droughts, and floods.
12 Key Messages from the chapter (abbreviated, but click here for the full description):
Key message 5.1
The atmospheric component of Canada’s water cycle has been altered and will continue to be altered by human influence (medium confidence). Total annual precipitation has increased and is projected to continue to increase (high confidence).
Total precipitation is projected to continue to increase, according to the report.
Key message 5.2
The greatest changes in streamflow magnitude across Canada have occurred and are projected to continue to occur on a seasonal basis. During the last 50 to 70 years, streamflow amounts have increased in winter and spring, and in some areas have decreased during summer (high confidence).
Key message 5.3
Annual streamflow amounts have increased in regions of northern Canada dominated by permafrost and will continue to do so (high confidence). No long-term historical or projected changes in annual streamflow are evident across the rest of the country (high confidence).
Key message 5.4
The timing of spring peak streamflow has shifted across Canada to earlier in the season because of the earlier onset of spring freshets. This shift has resulted in changes from more snowmelt-dominated streamflow regimes to rainfall-dominated regimes.
Key message 5.5
Over the period of observation, there is no indication of long-term changes in water levels in lakes and wetlands for Canada as a whole, and considerable regional and temporal variability is apparent. Levels are projected to decrease in some regions and increase in others (medium confidence) because of the many complex factors that affect surface water storage.
Key message 5.6
Groundwater recharge is anticipated to occur earlier in the year across the country, largely because of earlier snowmelt and more winter rain events (high confidence). The greatest changes in groundwater systems are expected to occur in northern Canada because of thawing permafrost, which may result in new groundwater pathways (medium confidence).
Key message 5.7
Groundwater is expected to remain one of the more resilient freshwater resources in a changing climate in comparison to surface water (medium confidence), given its naturally slow flow and enormous storage capacity, and if extraction through pumping does not markedly increase.
Key message 5.8
Meteorological and agricultural droughts are projected to be longer and more frequent and intense across central and southern Canada during summer, and to be more prominent with higher amounts of global warming and at the end of the century (high confidence). Summer hydrological droughts are also projected to be longer and more frequent and intense in many regions of southern Canada, mainly because of increased evaporation and lower runoff from mountainous regions (low confidence).
Key message 5.9
Over the period of observation, there have been no consistent trends in streamflow flood events across the country (high confidence). Streamflow-related floods in Canada are driven by multiple factors, including extreme precipitation, rapid snowmelt, rain-on-snow events, and ice jams, with complex interactions among these drivers.
Key message 5.10
Projected increases in extreme precipitation are expected to lead to more frequent and intense flash flooding across Canada (high confidence). Warmer temperatures are expected to lead to the earlier occurrence of snowmelt, rain-on-snow events, and ice jam breakups, resulting in earlier streamflow-related spring floods (medium confidence).
Key message 5.11
There has been a shift in the timing of many water cycle–related processes to earlier in the spring (high confidence). The shifts include earlier occurrences of snowmelt, spring freshet, groundwater aquifer recharge, and freshwater ice-free dates.
Key message 5.12
Canada’s water cycle has been altered and will continue to be altered by climate warming (medium confidence). This involves more precipitation, changes in the proportion of rainfall versus snowfall, increases in warm-season evaporation, and a greater potential for flash flooding and summer drought.
To read the entire summary for Chapter 5: Changes in the water cycle, go here: Chapter 5: Changes in the water cycle – Canada.ca
To read a summary of the whole report, go here