Flood Risk and Vulnerability Analysis Project - Atlantic Climate ...

Worst Case Scenarios
This section provided a preliminary assessment of weather phenomena or combinations
of weather events and other circumstances which, when occurring simultaneously or in
succession, can lead to significant flooding. While somewhat rare (an occurrence every
few years or less often), most of the scenarios have occurred in the past and are likely to
occur again, and so this section does not deal, per se, with highly unlikely events but
rather very plausible events (one could conjure up much worst case scenarios);
Considering, from the modeling work done here and reported elsewhere, the more
marked increases in temperature and precipitation in the winter season and supported
somewhat by updated IDFs, it is likely that winter rains will occur more frequently in the
coming decades which gives rise to a number of scenarios all starting with abundant
winter rains:
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Combined with sudden melting of the winter snow pack to produce a greater threat of
flooding especially likely for the West WRMD;
Together with sudden prolonged warming sufficient to break up river ice causing ice
jams as has happened at Badger in 2003, Central WRMD;
Falling on frozen ground unable to absorb the added moisture which did lead to a
major flood in Ontario in 1980 (noted again that Newfoundland may be especially
vulnerable given the thin soils);
Weather Bombs are explosively deepening low pressure systems typically starting in the
Cape Cod area and tracking just east of Newfoundland as they continue to intensify
rapidly. Such storms produce very strong (sometimes over 100 km/hr) wind bands
which can generate, thanks to a fetch of many hundreds of kilometers across the North
Atlantic, very significant waves. These are the „Nor‟easters‟ for which Newfoundland is
famous. They are a threat especially for the coastal communities on the eastern and
northern sides of the island of Newfoundland and it is speculated that they could
increase in intensity, but likely not in frequency, under a warming climate scenario.
Weather Bombs warrant closer examination, not possible here, given that they can
approach Hurricane intensity.
Hurricanes and tropical storms present the greatest threat of producing severe flooding
for Newfoundland. The intensity and frequency of tropical systems affecting
Newfoundland and neighboring waters has increased in the last several decades and
especially since 2000. Hurricane level storms, Category 1 and 2, have occurred but
remain rare events and so it is not possible to give precise return periods for these
especially given the cyclical nature of some of the oscillations that may influence them;
Many references support the argument that warmer tropical oceans together with
warmer waters in the North Atlantic will allow more tropical systems to maintain greater
intensity as they track northward along the east coast of North America. As such, it can
be said that a Category 2 or 3 hurricane making landfall in Newfoundland is likely, if not
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