Spatial distribution and prediction of local wind-driven rain intensity on building façades: Reduced-scale experiments and model validation

Wind-driven rain (WDR) creates highly nonuniform moisture loads on building façades, challenging waterproofing design and durability assessment. Existing WDR studies have emphasized overall exposure and spatial patterns, with limited attention to predicting local exposure across varying wind and rain conditions. This study conducted controlled indoor experiments on a reduced-scale façade model to characterize local WDR exposure. Analysis of 684 windward façade data points showed consistently high catch ratios in the upper and corner regions. Wind speed dominated variation in catch ratio, wind direction redistributed WDR between façades, and rainfall intensity mainly controlled water input. Within the experimental design, wind speed, wind direction, and rainfall intensity explained 74.30%, 20.13%, and 1.44% of the variance in mean catch ratio, respectively. A local WDR intensity model was developed by incorporating a position correction coefficient into an established semiempirical relationship. Validation yielded an RMSE of 0.371 mm/h, an MAE of 0.286 mm/h, and a relative bias of +1.06%. By extending WDR intensity prediction from façade-averaged to location-specific values, the model captures local exposure peaks and provides spatially resolved rain inputs for zoned waterproofing and hygrothermal simulations. It may also support targeted protection of traditional buildings exposed to long-term WDR.