Lisbon urban heat island in future urban and climate scenarios

Urban heat Islands (UHIs) may constitute a hazard for urban populations, particularly under extreme events such as heatwaves. Lisbon is a medium-size city regularly affected by heatwaves with maximum temperatures >35 degrees C and is expected to grow and densify during this century. This study evaluates the UHI in the Municipality of Lisbon (ML) for the heatwave with the highest maximum average temperature identified in long-term (2081-2100) RCP8.5 scenario climate simulations, relative to present conditions, represented by a typical heatwave identified in historical (1986-2005) period climate simulations. The expected future consolidation of the city (up to 2100) is considered, as well as the anthropogenic heat and irrigation effects. Simulations are performed with the Weather Research and Forecasting model (WRF) coupled with the Singlelayer Urban Canopy Model (SLUCM). The results reveal that urban irrigation effects compensate anthropogenic heat due to increased latent heat release. The expected city consolidation up to 2100 produces the largest increase in the UHI intensity (UHII) during nighttime due to the introduction of urban land use land cover (LULC) with reduced green fraction. No evidence of synergistic interactions between UHI and heatwave intensities were found, with the UHII mostly depending on wind direction and intensity.

Automated summary

Urban heat islands are a potential hazard for urban populations, especially during heatwaves. Lisbon, a medium-size city, is frequently affected by high-temperature heatwaves. This study evaluates the urban heat island effect in Lisbon under future climate scenarios, finding that irrigation can mitigate the anthropogenic heat.