Comparison of land surface temperature of local climate zones in Croatia and estimation of the vulnerable population heat risk

Cities are not homogeneous, but areas with similar microclimatic characteristics can be singled out based on land surface features, type of material, human activity, etc. These areas are called local climate zones (LCZ) and they are extremely important in the field of urban climatology. In this study, for the first time, we present LCZs for nine Croatian cities and their wider surroundings: Zagreb, Split, Rijeka, Osijek, Pula, Varaždin, Slavonski Brod, Zadar and Dubrovnik. LCZs were classified using the Local Climate Zone Generator web application. To analyse the thermal characteristics of LCZs in selected cities, we calculated the average land surface temperature (LST) and normalized difference vegetation index (NDVI) for the summer seasons 2017 - 2021 using Google Earth Engine, a cloud-based geospatial analysis platform. An approach for the heat risk estimation based on LCZ, LST and NDVI data is proposed and calculated for the locations of the facilities used by the vulnerable population. The heat risk classes for nursing homes and kindergartens were calculated for two largest Croatian cities, Zagreb and Split.

The results show high classification accuracy among nine cities, with an average of 83 %. Continental cities have higher accuracy as they historically expanded more evenly. On the other hand, coastal cities show slightly lower classification accuracy, which can be attributed to the confined expansion of the cities in the narrow coastal zone and to karst topography. Statistical analysis shows significant differences of LST among LCZs. In all cities, the highest LST values ​are associated with dense built-up parts (i.e. compact LCZs) but also with industrial zones. Out of natural LCZs, the highest LST is found in the karst hinterlands of the coastal cities, i.e. for LCZ E (Bare rock). Except for LCZ G (Water), the lowest values ​​of LST are obtained for forested areas outside the city and in city parks with dense trees, where LST is significantly lower compared to compact LCZs.

Estimation of the heat risk of the vulnerable population of Zagreb and Split shows that facilities with high heat risk are located in most built-up parts of the cities connected with high LST values, but a small share of vegetation. This analysis highlights the importance of the position of such facilities in the city from the aspect of reducing the heat load and improving the standard of life of the vulnerable population.