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

These increases, though slight, in the updated IDF values for Gander and Goose Bay, show
that more intense precipitation events are already beginning to register in recent years. The
projected curves for St. John‟s, Deer Lake and Stephenville, also show further increases in the
frequency and intensity of precipitation going forward to 2080. This provides a valuable
quantitative assessment of increases in precipitation leading to increased flood risk.
In the past, a set of IDF curves for a location, based on 50 or more years of past climate
records, was applied without further modifications in developing plans and designing
infrastructure with a life expectancy of 100 years or more. While updating IDFs is certainly still
very important since they capture the real full character of precipitation from all manner of
weather phenomena of all sizes recorded at a site, to use updated curves alone is no longer
valid in an era of rapid climate change. Projecting IDFs forward uses sophisticated techniques
and is highly recommended. But it must be recognized that the inputs used in making IDF
adjustments are largely derived from GCM outputs. Those, as discussed earlier, have difficulty
capturing some meso-scale weather phenomena and so may under-represent the return
periods for extreme precipitation events.
Finally, it should also be noted that precipitation, while a key element in determining flood risk, is
seldom the only factor leading to flooding. Other events such as storm surge, ice jams, spring
snow melt and even the saturation of the soil can all play a significant role as can other possible
future changes such as changing land cover. In addition, IDF curves do not capture the
seasonality of precipitation. As such precipitation and IDF values, while useful, should not be
examined in isolation.
3.4.3 Hurricanes and Tropical Storms
Historical track maps and data from the US National Hurricane Center (NHC) and the Canadian
Hurricane Centre (CHC) were utilized to study the occurrence of tropical system occurrences
over Newfoundland and Labrador, and its surrounding marine areas. For this report, tropical
storm activity from 1954 through 2011 was researched and divided into five regions based on
the storms track: Labrador, the three WRMD regions on the island of Newfoundland, and the
Newfoundland Marine Area (described as the Environment Canada Newfoundland and
Labrador marine districts north of Latitude 45.0 °N, shown in Figure 3-13). A particular focus
was to determine whether the frequency and intensity of tropical storms and hurricanes has
changed in recent decades and what can be said, if anything, about future trends.
TA1112733 page 59