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

West sees slightly larger winter increases while Labrador shows large steady increases in both
summer and winter. This represents an influence towards increased flood risk across the
Province, especially in winter for all WRMD regions. Winter thaws and rain events could lead to
increases in rain on snow flooding as has been pointed out by Catto and Hickman (2004).
Winter rains also lead to greater risk of rain on frozen ground events where the ground‟s ability
to absorb liquid is compromised.
3.4.2 Intensity Duration Frequency (IDF) Curves
AMEC has produced updated IDFs, for other projects, for Deer Lake and Stephenville
(representative of Western WRMD), and for St. John‟s (representative of Eastern WRMD); as
such it was decided to complete a simplified update of the IDF values for Gander
(representative of Central WRMD) and Goose Bay (representative of Labrador). Proceeding in
this manner would provide a current set of IDF curves for at least one representative location in
each WRMD region. Precipitation data was obtained from Environment Canada for several
sites in Newfoundland and Labrador and for a variety of durations. With regard to the case of
Gander, the original Environment Canada site had been moved. The location change in Gander
is considered negligible in terms of distance so it was felt that merging the new and old Gander
datasets and producing updated IDF values was valid. With regards to Goose Bay only daily
precipitation was recorded after 2009. Previously the IDF for Goose Bay was published as
being compiled up to 2007. As such the IDF values for Goose Bay were updated to 2009 with
the exception of the 24 h duration precipitation which was updated to 2011.
The technique used to update the IDF values is the same as used by Environment Canada, i.e.,
the statistics from the annual maxima at the various durations are calculated and a Gumbel
distribution is then employed using the various standard return periods. In addition, results were
calculated and included for the 1:20 year return period. The results of the updated IDFs for
Gander and Goose Bay, respectively, can be seen in Table 3-10 and Table 3-11. As such,
these updated IDFs then capture and characterise past precipitation events up to the most
recent years.
The changes to the IDF values at Gander are minor but most values increased compared to the
previously published value. Only one exception to this is evident, that being at very short
durations (5 minutes). The biggest changes are at the longer durations where there is an
increase of approximately 4% at all return periods compared to the previously published values.
There was almost no change in the values for Goose Bay. This is to be expected since only 2
additional years of data were considered (2007 to 2009) except for 24 hour precipitation (2007-
2011).
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