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
Figure 4-1 - Development of Adjusted Observed Climate Using the Delta Method
Simulated
Future
Climate
“Deltas”
Adjust
(Eqns. 1 & 2)
Current
Climate
Simulated
Overlap
Climate
Adjusted
Observed
Climate
In adjusting precipitation the ―delta‖ is in the form of a ratio as shown in Equation 1.
Psf
Pp
Pc
(1)
P
Where: P sf is the simulated future precipitation, P so is the simulated overlap
precipitation, P c is the current observed precipitation and P p is the projected future
precipitation.
so
In adjusting temperature, the ―delta‖ was in the form of an offset, as shown in Equation
2.
T
p
c
sf
so
T T T
(2)
Where: T sf is the simulated future temperature, T so is the simulated overlap temperature,
T c is the current observed temperature and T p is the projected future temperature.
The GLM also exhibits inherent bias. In principal every aspect of the method
Environment Canada uses to develop IDF curves could be duplicated which would allow
for exact replication of the historical precipitation intensities. However, once the
distributions are modified in the GLM framework to include covariates, the method and
results would deviate from those of Environment Canada. Further, the available GLM
fitting routines use different statistical packages and a different method of fitting
(maximum likelihood rather than the method of moments) than is used by Environment
Canada. Because these differences will introduce bias into the estimates of
precipitation intensities, a second application of the delta method was applied to adjust
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