Spatiotemporal Changes in Urban Heat Risk Driven by Intensifying Heatwaves in Global Warming Scenarios

The Coupled Model Intercomparison Project Phase 6 (CMIP6) provides global climate projections under multiple scenarios through the end of the century, facilitating dynamical downscaling simulations to evaluate the future impact of heatwaves on urban heat risk. However, the absence of future observational data makes it challenging to define heatwave events as simulation periods, while integrating high-resolution urban canopy models into long-term simulations leads to prohibitive computational costs. These limitations hinder the investigation of the spatiotemporal distribution of heat risk in target cities. 

This study employs the Weather Research and Forecasting (WRF) Model coupled with BEP+BEM, integrates gridded urban canopy parameters data, and focuses on the Tokyo metropolitan area as the study region. First, using CMIP6 data with a spatial resolution of 1.25°, we apply the percentile threshold method to identify and analyze heatwave events in the study area under the SSP245 and SSP585 scenarios for three future periods: 2025–2045, 2050–2070, and 2080–2100. Next, we employ an averaging-then-downscaling approach to obtain representative downscaled simulations of heatwave conditions for each period under different emission scenarios. Finally, we examine changes in urban heat island intensity and the spatiotemporal distribution of the Wet Bulb Globe Temperature (WBGT) during future heatwaves. Additionally, based on WBGT, we explore the most effective mitigation measures for reducing future heat-related health risks across different subregions. We believe this study provides a scientific reference for cities to adapt and respond to increasingly severe extreme heat events in the future.