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
The additional uncertainty arising from impact models is not ordinarily evaluated in
impact studies, as using multiple hydrologic models, each with multiple calibrations
along with multiple hydraulic or operations models, is simply too costly for most
agencies. However, it is important to recognize that decision-makers have routinely
relied on the results of impact models as the basis for planning and operational
decisions, and thus have implicitly accepted the uncertainties in those models.
This work involves a statistical model that, strictly speaking, serves as a second
downscaling method. The model takes as inputs projections of climate conditions,
downscaled to average conditions over a 1/2 degree grid cell and further downscales
those conditions to a single point, in this case the Deer Lake and St. John’s A Stations.
The model also relates monthly average conditions to monthly, and eventually annual,
extreme events. The model assumes that there is a causal relationship between
monthly values of the predictor variables (total precipitation and average temperature)
and monthly and annual maximum precipitation intensities, and that that relationship will
remain unchanged as climate evolves. It can be safely assumed that in strict terms this
assumption will not hold up, but it is the basis, at some level, of all estimates of future
conditions.
The results presented herein represent one estimate of the range of future extreme
precipitation intensity. That range is informed by the range of future projections of
monthly average climate conditions, which themselves reflect the range of emissions
scenarios and the different degrees of climate sensitivity among the GCMs. However, it
is exceedingly important to recognize that an ensemble of projections, such as the one
used in this study, may not capture the full range of uncertainty. That is, there is some
unknown and unknowable probability that the actual future conditions are not contained
in the range of projections in any given ensemble. Further, as noted above, there is
additional uncertainty inherent in the downscaling technique and the statistical model
that are not reflected in the currently-available ensembles.
Accordingly, the results of this work should be used in combination with all relevant
sources of information, including recent experience, and with careful professional
judgment.
AMEC Environment & Infrastructure 44