Expected heat load of Dubrovnik, Osijek, Rijeka, Zadar and Zagreb based on the projections of regional climate models

Abstract

This paper examines the expected future heat load in five Croatian cities: Dubrovnik, Zadar, Rijeka, Zagreb, and Osijek. The heat load is estimated by temperature-related climate indices and mean, maximum and minimum daily temperatures obtained by climate simulations using two different regional climate models (DHMZ-RegCM4 and SMHI-RCA4) with a horizontal resolution of 12.5 km, forced with two global climate models (EC-EARTH and MPI-ESM-MR/LR) for two different greenhouse gas concentration scenarios (RCP4.5 and RCP8.5). By comparing these variables for the period 2041–2070 with respect to the current climate (defined as that of the period 1991–2020), a significant increase in mean, maximum and minimum temperatures was observed in all analysed combinations of regional and global climate models for all analysed cities. Although there is a difference in results depending on the combination of regional and global models, the largest increase is mainly found in the warm part of the year (April-October), with the strongest warming of Dubrovnik and Rijeka. Due to similar trends in minimum and maximum temperatures, the trend in the daily temperature range is weak. Under warmer climate conditions, the number of days with a maximum air temperature above 25 °C increases in all considered cities (especially in Dubrovnik), as does the number of days with a minimum air temperature exceeding 20 °C (especially in Rijeka and Zadar). Furthermore, a reduction in the number of days with maximum and minimum temperatures below 0 °C is projected for all cities. Nevertheless, some differences are found between coastal and inland cities caused by local factors.