Thermal resilience under climate extremes: simulation-based assessment of heatwave impacts in informal buildings in Cairo

Climate change and rapid urbanization are increasing the frequency and intensity of heatwaves. Informal settlements are particularly vulnerable to heat stress due to inadequate housing conditions and socioeconomic constraints. In Egypt, informal housing accounts for 38.6% of the national housing stock, yet the risk of indoor heat stress remains underexplored. This study proposes a quantitative method to identify and classify heatwaves in Cairo and assess their impact on indoor overheating and heat-stress risk. Heatwave characteristics were analyzed for historical (2010–2024) and future (2050–2080) climates under the SSP2-4.5 and SSP5-8.5 scenarios. Indoor overheating was evaluated for three building types (Tower, Amara, and Typical) within a representative informal settlement using EnergyPlus. The standard effective temperature ( SET ) was used to assess thermal resilience and heat-stress risk. Field measurements during typical and extreme summer periods were conducted to calibrate the model. Results indicate that heatwave duration has a greater influence on indoor severity than peak outdoor temperature. The Tower building and top floors were the most vulnerable during historical periods. Under future climates, the Typical building exhibited the highest indoor severity, with cumulative SET exceedance above 31.2 °C reaching 11,638.82 °C·h on the top floors under SSP5-8.5 (2080). By the 2050s, all building configurations exceeded the survivability thresholds during prolonged heatwaves, emphasizing the need for targeted cooling strategies and heat-risk policies that prioritize informal housing in climate adaptation planning.