Accurate hygrothermal simulations are essential for assessing moisture safety in buildings, particularly under future climate conditions and extreme events. While the impacts of urban microclimates on energy performance, thermal comfort, and health have been extensively studied, their influence on hygrothermal simulations remains underexplored. This study addresses this gap by evaluating the impact of including high-resolution microclimate data in hygrothermal simulations, using a prefabricated wooden wall assembly in Stockholm, Sweden, as a case study. A validated high spatiotemporal resolution microclimate model is used to downscale mesoscale historical and future climate (2050) data into microscale. Hygrothermal simulations and mold growth calculations are then conducted using both mesoscale and microscale climate data, under typical and extreme weather conditions, and with two wind-driven rain models. The results indicated that relying solely on historical climate data substantially underestimates future hygrothermal risks, particularly during extreme warm conditions, where moisture content rose by up to 61% and the estimated mold index substantially exceeded the critical risk threshold. Comparing microscale and mesoscale climate data revealed about a 17% increase in summer peak temperatures and up to a 25% reduction in wind speed. Incorporating microclimate data into the simulations further amplified moisture risks: for example, moisture content increased by up to 3.5%, and mold index values rose significantly under extreme warm conditions. In contrast, microclimate data had a limited impact under typical and extreme cold conditions but still introduced uncertainties that could lead to under- or overestimation of moisture risks. Overall, these findings highlight the importance of including detailed microclimate data in hygrothermal simulations to improve risk assessments and support moisture-safe building envelope design for future urban climates, particularly during extreme events.