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Photo by: Mitch Miller

River Temperatures and Flow

River temperatures fluctuate naturally with the Meanwhile, increased precipitation in the fall and
seasons, but, on average, river waters will warm winter is likely to create more frequent high river
as our air temperatures increase . During summer flow and runoff events, particularly because less will
hot spells, river temperatures can exceed the fall as snow . This can cause overland flooding and
threshold of what some aquatic species require erosion along rivers, which could threaten homes
to survive . and other structures . Heavy rainfall events also have
the potential to destabilize slopes, which could
With snowmelt occurring earlier in spring and trigger mass movement events like landslides, as
early summer, there will be less flow for rivers well as lead to blockages of logs and other debris,
in later months (CRD 2017) . As a result, smaller causing rivers to overflow their banks . We observed
southern rivers in British Columbia may dry up all of these consequences in November 2021, when
during summer and early fall — resulting in possi- a series of intense 'atmospheric river' storm events
ble stranding of rearing populations of salmon in dumped record rainfall across southern British
ephemeral or side channel habitats . Low fall flows Columbia . This flooding is likely to be the most costly
also can impact the critical spawning window for natural disaster in Canadian history due to all the
Pacific salmon (MOE BC 2016) .
infrastructure and property damage (Judd 2021) . It
This combination of warmer river waters, and is expected that the event will severely affect several
lower river flows and water levels can impede populations of salmon (Nair 2021) . Higher flows will
spawning salmon migration, since at times they impact salmon habitats by lowering water clarity
will need to wait for water to cool and levels to due to increased sediment inputs, scouring spawn-
increase . As the fish mill in estuaries and lower river ing gravel and threatening the stability of riparian
areas waiting for flow levels to increase, they are vegetation that provide salmon shade, cooler waters
subject to increased predation and pre-spawning and insect food sources (MOE BC 2016) . Stronger
stress . This unfortunate combination is projected flows could potentially make migration much more
to occur more often and will affect the ecosystems difficult for Pacific salmon, and wash away salmon
and communities that rely on salmon (see Chapter 3) . eggs from their redds (nests) in the gravel .

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