Winter gains versus summer losses - the impact of urban heat island on energy consumption in middle sized cities of north-eastern Romania under climate change

Nowadays, one of the major challenges posed by the combined effects of urban heat island (UHI) phenomenon, extensive urbanization, and climate change is represented by the increased energy demand for household cooling and heating. Our analysis focuses on 4 middle sized cities from north-eastern Romania (Iași, Bacău, Botoșani and Suceava) facing both high energy demand for winter heating, but also an increased demand for summer cooling, driven by the more frequent heatwaves occurred in the recent climate change context. The trend analysis made on long-term RoCliB dataset underlines that the cooling demand increases over the analyzed cities after 2005 (+ 50-100 CDD per decade), while the heating demand has shown a more gradual decline after 1990 (- 100-200 HDD per decade).

The study is primerly based on a three-year timespan (2023-2025)  of hourly air temperature measurements collected at paired observation sites located in the central areas of the analyzed cities and their peripheries, capturing the peak intensity of the UHI effect. Additionally, the hourly data  is supplemented  with data from mobile measurements to refine the UHI intensity estimates. The analyzed cities exhibit a UHI intensity of about 1°C at the annual mean level, reaching its maximum intensity during the summer nights (2-3°C).

Based on this dataset, heating and cooling degrees are firstly computed for the paired stations to outline the difference imposed by the UHI. Generally, the cost for winter heating (>25000 HDD) compared to summer cooling (5000 CDD) for a household is 5 times higher, while the need for heating/cooling manifests during 250/120 days, with a difference of 5 days for both between cities center and their periphery, imposed by the UHI.  As well, from our assessment at the individual household level, the higher energy costs for cooling in the UHI core during the warm season are offset by lower heating costs in the cold season.

However, the higher density of households in the central area of the cities tends to shift the overall energy demand toward increased summer cooling in the future. The shift in energy demand imposed by the UHI toward less winter heating and more summer cooling is afterthat extrapolated for the next decades using future climate models projections accessed from RoCliB dataset over Romania. The results can help stakeholders strengthen climate resilience in building performance and energy demand.

Acknowledgement. This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS - UEFISCDI, project number PN-IV-P1-PCE-2023-0897, within PNCDI IV.