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
maximum for each case. Then, the ratio of the calculated baseline annual maximum
and the calculated projected annual maximum is used as an estimate of the climate
sensitivity of the annual extreme precipitation. This calculated climate sensitivity is then
used to adjust the historical precipitation intensities in the same manner as is shown in
Equation 1.
4.7 Treatment of Uncertainty
All measurements contain uncertainty, and estimates of future conditions are more
uncertain than measurements. Each element of a climate impact analysis contains its
own degree of uncertainty. These individual uncertainties do not add up in a
straightforward way, but they do interact and each added element does increase the
overall uncertainty of the final estimate of impact. The approach adopted for this work is
intended to make the uncertainty arising from climate models as apparent as possible,
so as to allow well-informed judgments regarding future water resources planning.
In North America, the available projections from GCMs show that temperature is highly
likely to increase. However, projections of future precipitation are more uncertain; e.g.
in some parts of North America model projections disagree on both the sign and
magnitude of changes in precipitation. The sources of this uncertainty include the data
and structure of the GCMs, the methods used to relate GCM projections to points or
small areas on the earth’s surface (downscaling), and the projections of future
greenhouse gas emissions. Regardless of its source, uncertainty should at least be
recognized and ideally should be quantified when climate projections are used for
planning purposes.
As a practical matter, uncertainty in climate projections manifests in disagreement
between individual projections of future climate conditions and impacts. There are 48
statistically downscaled projections of future climate conditions (monthly average
temperature and precipitation) that are readily available for the study area. The most
comprehensive picture of uncertainty in future conditions can be obtained by analyzing
a large ensemble of projections, as recommended in the CSA Technical Guidelines.
Accordingly, all of the available projections have been used to produce, for each
duration period and frequency, an ensemble containing 48 estimates of precipitation
intensity.
Neither the climate projections nor the results have been broken down according to the
SRES emission scenarios because the intention was to represent the uncertainty in
climate projections collectively, regardless of source.
The overall results report the ensemble mean, the ensemble maximum and the 90 th
percentile non-exceedance value for each intensity estimate. How to interpret the range
AMEC Environment & Infrastructure 26