The contribution of urbanisation and climate conditions to increased urban heat load in Zagreb (Croatia) since the 1960s

Urban climate is affected by weather, global climate change and urban development. However, climate change and urbanisation take place simultaneously with intertwined impacts. To analyse their relative contribution to the heat load of Zagreb, a modelling approach is applied to two land-use/land-cover (LULC) situations and corresponding climate conditions. The results indicate that the change in total heat load is dominantly affected by climate change (-88%) with an average increase in the summer days for 35 days. LULC alterations have a weaker impact (-12%), but they strongly affect heat load spatial variability. The sign of LULC related heat load change de-pends on the type of the change (e.g. an increase is detected in areas that have turned from green into built-up classes). Generally, LULC effect is limited to the area with the modification, however it can spread to adjacent areas due to the processes like advection and evapotranspiration. In areas with considerable LULC alterations, their impact on the heat load is comparable to that of climate change. These results highlight the potential of change in the city infrastructure for climate adaptation, as well as emphasise the importance of considering future climate conditions when assessing efficiency of climate adaptation measures.

Automated summary

Urban climate is impacted by weather, global climate change, and urban development. This study reveals that climate change has a dominant effect on the heat load of Zagreb, while land-use/land-cover changes have a weaker impact but significant spatial variability on heat load.