Heat hazard and risk assessment in urban areas. Case study of Bucharest (Romania)

Climate and climate-related hazards are growing threats to our cities, as a result of the twin challenges derived from the warming climate and urban expansion. Accountable development strategies must take into consideration the safety of the urban population, including its vulnerability and exposure to different hazards. The evaluation of risks related to heat hazards is a priority for urban municipalities, especially in big cities where the urban heat island intensity is significant. For example, the urban perimeter of Bucharest (Romania) is 2 - 3°C warmer than the 5 km buffer of the rural neighborhood, as an average of the land surface temperature (LST) over the summer months.

This research explores the risk associated with the heat hazard occurring over Bucharest due to vulnerabilities derived from different urban elements, such as population, land cover-land use, local climate zones, and characteristics of the buildings. The analysis covers the period 2013-2022, and the outputs are delivered at 100-m spatial resolution. The heat hazards were derived from LST retrieved from high-resolution imagery (i.e. Landsat 8) data using emissivity estimation, and the urban risk was calculated based on several variables related to demographics and built environment, considering their influence on the vulnerability to heat hazard. The Heat Hazard-Risk was computed using a risk matrix approach, as a product between the heat hazard and vulnerability, and the results inform the level of Census Administrative Units (CAU).

The results show that the heat hazard is more frequent during the warm season, and especially in June-July-August, when the average daily LST exceeds 40°C over the largest part of the city. The land cover characteristics and the LCZ have a significant influence on the LST values and generate adverse impacts on health, economic activities, and the environment.

As regards the demographic profile, this study examines the consequent risk derived from (a) population size (i.e. number of inhabitants and density), (b) age (i.e. younger and older people), and (c) density of people in the same dwelling.

This study has been partly funded by the project Synergies between Urban Heat Island and Heat Wave Risks in Romania: Climate Change Challenges and Adaptation Options (SynUHI) PN-III-P4-PCE-2021-1695.