Granular mapping of UHI and heatwave effects: Implications for building performance and urban resilience

• Comprehensive analysis of the Urban Heat Island (UHI) effect during heatwave phases in Madrid. • Projections reveal up to 30 prolonged heatwaves lasting 102 days in future climate scenarios. • Multi-Criteria Decision Analysis (MCDA) identifies urban density and infrastructure as key amplifiers of UHI effects. • Green infrastructure and NDVI demonstrate cooling effects but have limited efficacy during extreme heatwaves. • Findings emphasize the need for integrated resilience strategies combining green and innovative cooling solutions. This study presents a comprehensive framework for addressing the growing challenges posed by the Urban Heat Island (UHI) effect on heatwave (HW) phases in urban environments. By generating customized, high-resolution weather datasets (EPW) that capture both spatial and temporal variations of UHI across different periods, this framework is applied to the Canillas neighbourhood in Madrid, providing valuable insights into the UHI-HW interactions specific to this urban area. Through the analysis of historical, mid-term, and future climate scenarios, the findings reveal a concerning trend: While the frequency of HW events may decrease, their duration and intensity are projected to increase significantly. Future climate scenarios suggest the possibility of up to 30 heatwaves occurring annually, with a combined total duration of 102 days. Moreover, UHI within an urban cell exhibits varying intensities and sizes depending on the region and measurement time. The use of Multi-Criteria Decision Analysis (MCDA) sheds light on how factors such as building density, road infrastructure, and building height amplify UHI effects, driving temperatures in densely developed areas above 37 °C during HW. Depending on the urban geometry, there is a difference between the amount of heat and the time it takes to release that heat. While urban vegetation has a cooling effect, its ability to mitigate extreme temperatures during intense HW is limited, emphasizing the need for green infrastructure as a foundational, though inadequate, solution when applied alone. Additionally, analyses using the Normalized Difference Vegetation Index (NDVI) reveal a strong inverse relationship between vegetation and temperature, particularly during historical periods. However, this effect is expected to diminish in the future, underscoring the need for innovative resilience strategies such as: such as cool roofs, reflective surfaces, or green rooftops, as traditional approaches may no longer suffice in the face of intensifying climate change. Therefore, this study offers crucial insights to bolster urban resilience, emphasizing the need for the strategic integration of green infrastructure, innovative cooling solutions, and balanced urban density to mitigate the combined effects of the UHI phenomenon and HW in cities experiencing rapid warming.