National Building Codes and Climate Change Considerations
The Building codes are starting to consider how to include climate change effects in the engineering design and analysis of structures such as towers. For example the S37 is now suggesting that Engineers should keep current with the climate change literature in order to factor in the results of climate change models into their work.
Environment Canada has set up a climate-scenarios web site which provides the results of various scenario and model runs for use by professionals in the Engineering Field. Since the government is not able to predict which of the CO2 scenarios is most likely to materialize, it will be hard for the Engineer to determine the change that he should build into the analysis.
ICE Support for Climate Change Decision Making
The changes to the extreme wind and its recurrence interval are expected to arise from a number of factors, including
1 Change in the intensity of severe weather events (eg. deeper extra-tropical depressions)
2 Change in the frequency of such events which determines the mean recurrence interval
3 Change in the intensity and types of precipitation events
4 Validity of the stationarity assumption in performing the statistics.
Scientists at the World’s main Meteorological Prediction Centres (NWS NOAA for US, ECC for Canada and ECMWF for Europe) have developed Global Atmospheric circulation models coupled with Ocean circulation models and applied future GHG (Green House Gas) concentration forcing in an effort to produce a simulation of the future behaviour of the Earth’s atmosphere.
These models have been run with several alternative RCP (Representative Concentration Pathways) scenarios to produce hourly weather data out to the end of the century. Each RCP pathway represents a projection of alternative emission reduction strategies over the next 50 to 100 years, producing different amounts of Global Warming.
At ICE we use the Canadian Environment and Climate Change Model gridded output data from the high resolution regional runs to extract the maximum monthly surface wind speed over a 30 year period starting in 2070 and for the same location extract the 30 year monthly maximum wind dataset for the current (historical model run) period. We then perform statistical analysis to determine the 50 yr return wind for each of these and calculate the relative change in return period wind.
This relative change is then applied to the site specific wind derived from historical airport data for the site using ICE Inc. site specific procedures to project the airport derived extreme wind to the future climate period.
The site specific report then provides the expected change in the extreme wind estimate out 30 to 60 years into the future.
As the climate assumptions change over time to reflect the most likely effect of emission reductions and other climate measures, and as the climate models are improved and rerun with the new global warming estimates, the projection can be updated based on the new model runs.