Urban Heat Island, Air Pollution, and Climate Change: The Bologna (IT) iSCAPE Case Study

Acquiring knowledge about the interactions between urban climate, air pollution and climate change in European cities is at the core of the ongoing EU funded project iSCAPE (www.iscapeproject.eu). In this work we address the linkage between expected climate change in the metropolitan area of Bologna (Italy), which is one of the pilot cities in iSCAPE. Bologna is located in the lower eastern part of the Po-Valley, a hot-spot in terms of air quality, climate change and urban heat island (UHI) dynamics. According to the latest findings in the region, the annual mean daily maximum temperature increase of 0.11±0.01 °C per decade over the period 1865-2003 exceeds the corresponding trend for daily minimum temperatures of 0.09±0.01 °C per decade (Brunetti et al., 2006). Occurrence of heat waves in the region is projected to increase in the future (Zampieri et al., 2016) and coupling with UHI is expected to have strong impacts on local circulation, pollutant dispersion patterns as well as human comfort. The approach we follow builds upon a recent work by Conry et al. (2015), where a one-way, offline nesting procedure using several models is used to assess the effects of climate change on UHI. The Numerical models used in cascade include a global climate model (CAM at around 200-km resolution), a mesoscale model (nested WRF-urban down to 0.333-km resolution), and the latest version of the microscale model ENVI-met 4.2 where individual buildings are resolved. Model simulations are validated using data being acquired during an extensive experimental campaign in Bologna city center in summer 2017. A suite of instruments is being deployed in two neighborhoods to evaluate profiles of turbulent fluxes of momentum, heat, CO₂ and H₂0, air temperature via distributed sensors, surface temperature using infra-red camera, radiative temperature for human comfort analyses, measurements of particulate matter, ozone and traffic-related compounds concentrations. Data are also integrated with boundary-layer measurements using the Vaisala ceilometer CL31 and radiosonde soundings available from a nearby station. Stand-alone preliminary model runs using WRF version 3.8 and validated using several weather stations show that in presence of a heat-wave (the worst condition for the urban environment in south European cities, such as the one that occurred in July 2015 and the one still under way in 2017), the UHI contribution exceeds rural temperatures of 2-4 °C during the night. These findings, may have relevant consequences for air quality, ozone production, human comfort, energy consumption and water management in the area. The paper proposes the methodology as a possible way to gain information about the expected changes in urban air quality due to the sole change in meteorology in future climate scenarios. This could serve as a basis for the implementation of strategies to mitigate the effects of climate change on temperature and air quality in urban areas.

Acknowledgement

The iSCAPE (Improving Smart Control of Air Pollution in Europe) project is funded through the European Community’s H2020 Programme under the Grant Agreement No. 689954.

References

Brunetti, M., Maugeri, M., Monti, F. and Nanni, T. (2006) Temperature and precipitation variability in Italy in the last two centuries from homogenised instrumental time series. International Journal Climatology, 26: 345–381. doi:10.1002/joc.1251

Conry, P., Sharma, A., Potosnak, M.J., Leo, L.S., Bensman, E., Hellmann, J.J., Fernando, H.J.S. (2015) Chicago's heat island and climate change: Bridging the scales via dynamical downscaling. Journal of Applied Meteorology and Climatology, 54:1430-1448

Zampieri, M., Russo, S., Di Sabatino, S., Michetti, M., Scoccimarro, E., Gualdi, S. (2016) “Global assessment of heat wave magnitudes from 1901 to 2010 and implications for the river discharge of the Alps” Science of the Total Environment 571:1330-1339