Olivier Giot

Future Climate and Air Quality of the Brussels Capital Region for the 2050s Under A1B Scenario

Within the framework of the ACCEPTED project (an Assessment of Changing Conditions, Environmental Policies, Time-activities, Exposure and Disease), a high-resolution urban dynamical downscaling technique has been applied for the Brussels Capital Region. First, regional climate simulations were performed with a new version of the limited-area model of the ARPEGE-IFS system running at 4-km resolution called ALARO coupled with the Town Energy Balance scheme (TEB). Then, to further downscale the regional climate projections to an urban scale, at 1 km resolution, a stand-alone surface scheme was employed in offline mode. Downscaling simulations of present and future urban climate of the Brussels areas are conducted. The downscaling strategy was first evaluated for a 10-years period [2001–2010] using ERA-INTERIM re-analysis data. In a next step, a downscaling simulation for the period 2046−2055 under the A1B scenario was performed. Results from our simulations indicate that while both urban and rural areas warm substantially for the 2050s horizon (1.5 °C), climate change will have a neutral impact on annual mean urban heat island (UHI) intensity. The most important increase is noted for the nocturnal UHI during the winter (+15 %) and the most important decrease is noted for the daytime UHI during the summer (−43 %). However, the model projects an increase of stable situations in the lower atmosphere during winter which may tend to keep pollutants concentrated over urban areas, with the associated health effects. Two approaches have been used to examine meteorological conditions that are unfavorable for the dispersion of air pollution under climate change conditions: (i) a transport index, based on the wind speed and Brunt-Vaisala frequency, that characterizes a typical length of horizontal and vertical transport, (ii) state-of-the-art chemistry transport models CHIMERE coupled to the 4 km regional climate simulations. The results from both approaches will be compared to assess future concentrations at the urban scale.