Evolution of urban heat wave intensity for the Brussels Capital Region in the ARPEGE-Climat A1B scenario

Urban areas are particularly vulnerable to heat wave (HW). This paper will examine the important question on urban heat island (UHI) during HW and their interactions under present and future conditions. Therefore, a 1 km-resolution urban dynamical downscaling technique has been applied over the Brussels Capital Region. Results from observations, ERA-Interim driven simulations (1981-2010), present (1990-1999) and future (2046-2055) climate simulations under the A1B scenario of the global climate model ARPEGE-Climat indicate that for the present climate: (i) observed nighttime UHI is enhanced under HW by 1.5 °C (0.6 °C ERA-Interim), (ii) due to a dry summer bias in ARPEGE-Climat, the control simulation was not able to reproduce the UHI intensification during HW, and (iii) in the ERA-Interim runs, HW affects urban and rural surface energy balance differently. Hereby, the HW definition and heat stress index are based upon the warnings issued by the Public Health of Belgium. For the 2050s, climate change increases, statistically significant, the intensity of HW for urban (rural) areas during the night (day). Under future HW, the biggest and statistically significant increase of the ratio of number of hours to number of days while the Humidex is above dangerous (> 40) thresholds occurs over urban areas.