Projected changes to moisture loads for design and management of building exteriors over Canada

Atmospheric moisture loading affects the performance and durability of building exteriors. In a changing climate, designing for historical moisture loads may no longer be adequate. This study investigates potential climate change impacts on the moisture index used in the design and management of buildings over Canada. Projections are obtained for future periods experiencing different global warming levels (+1 degrees C, +2 degrees C, etc.) with respect to 1986-2016 baseline using outputs from a 15-member initial condition ensemble of the CanRCM4, a Canadian regional climate model at 50-km resolution. CanRCM4 overestimates wetting potential, underestimates drying capacity, and hence overestimates moisture loads for the baseline period. To obtain unbiased moisture indices, a simple linear bias adjustment scheme is applied to the baseline simulation and future projections. Significant increases in future moisture loads are found over the western and eastern coastal regions of Canada due to increases in rainfall amounts, driven by increases in precipitation and a warming-induced shift from snow to rain. Conversely, CanRCM4 projects significant decreases in future moisture loads over south-central and northern Canada due to increases in drying capacity, driven by increases in future near surface air temperature that are accompanied by nearly unchanged relative humidity. Internal variability of the moisture load due to the natural, chaotic variability of the climate system, is modest compared to the magnitude of the projected change signal - signal-to-noise ratio is high. The projected changes suggest that moisture protection could be a concern for designing and managing building exteriors over western and eastern coastal regions of Canada.