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

Development of Projected Intensity-Duration-Frequency Curves
for Corner Brook and Goulds/Petty Harbour, Newfoundland May 16, 2012
In 2010, Environment Canada developed updated IDF curves based on historical
observations from the stations at Deer Lake (data from 1966 through 2002), St. John’s
A (data from 1949 through 1996), and Stephenville A(data from 1967 through 2007).
The documentation for these historical IDF curves included the record of the intensity of
annual extreme precipitation events for nine event durations ranging from 5 minutes to
24 hours. Another historical IDF curve was developed by CBCL Limited based on a
combination of data from the St. John’s A station and a second station at Windsor Lake,
nearby (data provided by WRMD). To obtain projected IDF curves, the precipitation
intensities in the historical IDF curves were adjusted to reflect projected changes in
climate using a statistical modeling technique that is described briefly in the following
paragraph, and in more detail in the following sections of this report.
The approach selected for this work uses a statistical model that derives the sensitivity
of extreme precipitation to climate conditions from the historical climate information for a
site. In this case the historical climate was characterized by observations of monthly
average temperature and monthly total precipitation at the Deer Lake, St. John’s A and
Stephenville weather stations. The statistical model, which is described in more detail
below, was fitted to the local climate data and the historical monthly precipitation
maxima using a form of regression. Information about future monthly average
temperature and monthly total precipitation was obtained from the output of 48 runs of
GCMs. Each GCM run was compared internally to establish a projected future change
in temperature and precipitation. These changes were used to adjust the historical
record of temperature and precipitation to reflect future conditions, which resulted in 48
future climate scenarios that were based on the historical record but which reflected the
projected future change in climate. This approach, which is referred to as the delta
approach, is used to reduce some of the inevitable bias inherent in projections of future
climate.
The statistical model of extreme precipitation was then run against each of these
adjusted records to obtain estimates of climate-impacted extreme precipitation
intensities for each of the nine durations and six return intervals. These estimates
reflect the bias in the statistical model, so one more run of the statistical model was
made against the average historical climate conditions to provide a baseline set of
extreme precipitation intensities. This set of baseline intensities was compared against
each of the 48 estimates of climate-impacted intensities to determine the change in
intensity attributable to the change in climate. These changes were then used to adjust
the values in the historical IDF curve to obtain the final projected values of precipitation
intensity. (This is another application of the delta approach.)
The 48 projections used to characterize future climate conditions produced an equal
number of estimates of projected precipitation intensities for each duration and return
AMEC Environment & Infrastructure 2