Urban Heat Load in a Small Mediterranean City in Recent, Extreme and Future Climate Conditions—A Case Study for the City of Dubrovnik

This article examines the urban heat load (UHL) of Dubrovnik, a small Mediterranean city located in the complex terrain of the eastern Adriatic coast. In the study, the characteristics of the UHL are investigated in three special scenarios that mimic the different climate conditions: the recent climate (1981–2010), the hypothetical extreme climate (consisting of the 10 years with the hottest summers in the period 1961–2021) and the future climate (2041–2070) according to the RCP4.5 scenario. The UHL is quantified in terms of climate indices with fixed thresholds, defined as the annual number of days on which the daily minimum or maximum temperature exceeds certain thresholds. The analysis was carried out using the microscale urban climate model MUKLIMO_3. In addition, the potential benefits of certain measures to reduce UHL were investigated. In relation to the recent climate, the results show an increase in the amplitude of UHL under extreme and future climate conditions, with the UHL being strongest under the projected future climate conditions. In all three scenarios, the UHL is the highest in the built-up parts of the city. However, a strong increase in UHL is obtained in the green parts of the domain indicating a possible reduction in the cooling capacity of green areas under warmer climate conditions. Applied land use/land cover (LULC) changes of the model area, which include changes in the albedo of roofs, the proportion of low vegetation, impervious surfaces and built-up areas, have some influence on the reduction of UHL, but their effect is quite weak and mostly local. The greatest effect on reducing diurnal UHL is achieved by changing albedo, while the most effective reduction in nocturnal UHL is achieved by a combination of changes in albedo, the proportion of low vegetation, impervious surfaces and built-up areas. Considering the relatively weak cooling effect of the LULC modifications and the potential reduction in vegetation efficiency under warmer climate conditions as well as the expected increase in heatwaves, it is likely that Dubrovnik will suffer from extremely high UHL in the future.