Projected changes to risk of wind-driven rain on buildings in Canada under +0.5 °C to +3.5 °C global warming above the recent period

Abstract

Wind-driven rain (WDR) on building façades reduces hygrothermal performance and durability of wall assemblies. This paper evaluates projected changes to WDR exposure of building façades in Canada for future periods corresponding to specified levels (0.5 ~ 3.5 °C) of global warming above the 1986–2016 baseline. Projections are based on a large ensemble of Canadian Regional Climate Model (CanRCM4) simulations forced at the boundaries by the Canadian Earth System Model (CanESM2) under a business-as-usual emission scenario (RCP8.5). Annual and spell-specific timescale WDR indices are estimated from hourly meteorological variables using the semi-empirical approach of the International Organization for Standardization. The CanRCM4 ensemble reproduces spatial patterns of observed annual total rainfall, mean wind speed, and driving-rain index for the baseline period. However, the CanRCM4 ensemble overestimates observed annual and spell indices by 22 ~ 91%, due to its overestimation of rainfall amounts and wind speeds. Significant increases in annual and extreme spell indices of WDR are projected in the future, with larger increases seen over western and northern Canada and at higher global warming levels. These increases are mainly driven by the increases in rainfall amounts due to both increases in precipitation magnitude and the shift in phase of precipitation from snow to rain caused by warming. Increases in WDR exposure become an emerging future consideration for moisture-resilient design and management of buildings, especially in western and northern Canada. However, as the fidelity of the CanRCM4 simulations of WDR is limited by the model’s coarse spatial resolution, which affects its ability to simulate local hourly rainfall, wind speed, and wind direction, future WDR exposure should be evaluated further when higher resolution simulations become available.