How are the future weather files developed by the Pacific Climate Impacts Consortium (PCIC) and the National Research Council of Canada (NRC)?
The future weather files developed by PCIC and NRC are different in terms of:
- The downscaling technique used to provide climate model outputs at the finer resolution required for direct use in building simulation; and
- The techniques used to incorporate future climate data into the weather files.
To obtain suitable climate information for building simulation from GCM output, PCIC statistically downscaled and bias adjusted daily climate projections from an ensemble of 10 climate models. For dry-bulb temperature values, PCIC used the BCCAQv2 methodology to downscale climate projections from GCMs to a gridded resolution of roughly 10 km x 6 km. For dew-point temperature, relative humidity and surface pressure, climate projections from the GCMs were only interpolated to the BCCAQv2 resolution.
Next, PCIC incorporated these statistically downscaled and bias adjusted projections into weather files using the “morphing technique”1. The morphing technique applies three transformation functions (shift, stretch, and their combination) to adjust the hourly values of any given variable stored in a historical weather file. For this reason, PCIC’s future weather files are often referred to as future-shifted weather files. The process of applying the projected climate change to the historical CWEC weather files highlights the importance of the period of record as any differences in this period will propagate to the future weather files.
Adjustments to hourly values in PCIC future-shifted weather files are applied to dry-bulb and dew point temperatures, relative humidity, and surface pressure. All other variables stored in the historical weather file remain unadjusted. Therefore, the hourly values of solar radiation, wind speed/direction, cloud cover, etc., in the historical weather file – CWEC2016, period of 1998 to 2014 – that is used as the baseline period of record and the three generated future weather files are identical. The results are three, 30-year future-shifted weather files, using RCP8.5, for the following time-periods: 2020s (2011 to 2040), 2050s (2041 to 2070), 2080s (2071 to 2100).
Future weather files developed by NRC are obtained directly from dynamically downscaled and bias adjusted climate projections using the second-generation Canadian Earth System Model, CanESM2 (A coarse resolution global model). This work was built upon the framework developed by the Climate-Resilient Buildings and Core Public Infrastructure (CRBCPI) project, where the CanESM2 large ensemble – consisting of 50 simulation runs of the CanESM2 model with different initial conditions – was dynamically downscaled using the Canadian Regional Climate Model Version 4 (CanRCM4). NRC used a subset of the CanRCM4 large ensemble simulations comprising of 15 runs to acquire the climate projections. Some climate variables were not directly available from the CanRCM4 large ensemble at hourly scale and hence were estimated: rainfall (from precipitation), snow-cover (from snow-depth), as well as direct horizontal, direct normal, and diffused horizontal solar radiation (using established methods from literature).
NRC used the following steps to generate their future weather files:
- Eight 31-year long time-series were extracted from each of the 15 CanRCM4 runs to include one baseline (1991 to 2021) – produced from the modelled historical data, and seven future periods expressed according to levels of global warming: +0.5°C, +1.0°C, +1.5°C, +2.0°C, +2.5°C, +3.0°C, and +3.5°C.
- The climate time-series were bias adjusted with reference to station level observations from ECCC’s Canadian Weather Energy and Engineering Datasets (CWEEDS) database.
- Using the CWEC procedure (based on TMY method), Typical Meteorological Year (TMY) files of current and future periods were prepared for each level of global warming.
- The NRC team calculated the corresponding time-periods for each level of global warming by determining the year for which average global temperatures in CanEMS2 exceeded each level (+0.5 to 3.5°C) relative to 1991 to 2021 period. This year was then used as the center of the 31-year time-periods.
- Using a temperature-based method2, Typical Downscaled Year (TDY), Extreme Cold Year (ECY) and Extreme Warm Year (EWY) of current and future periods were prepared for users that are interested in both, typical and extreme subsets of the data for building applications.
- For buildings moisture performance applications (i.e., hygrothermal simulation), the Moisture Reference Year (MRY) comprises of a conditioning year (median year) and extreme year (10%-year) that was prepared based on Moisture Index3.
More detailed information on the future weather files method can also be accessed in PCIC and NRC’s technical documents. For guidance on using these future weather files, see the article “Guidance on Using Future Climate Data for Building Performance Simulation”.