We address the seasonal dependency of the urban heat island (UHI) intensity and its climatic drivers at the mid-latitudes based on model-based sensitivity experiments over Belgium. Hereby, the used new urban land-surface model TERRA-URB employed in this study is tested for an annual observation dataset of the CAPITOUL campaign at a dense urban site in Toulouse centre rst. These oine model results demonstrate that TERRA-
URB is able to reproduce the urban surface-energy balance including its seasonal variability. Afterwards, TERRA-URB is coupled to COSMO-CLM over Belgium during 2012, which shows that such model setup can reproduce the seasonal, daily and diurnal variability of the UHI intensity of cities in Belgium as well. It is a common perception that the presence of the urban fabric (UF) is the dominant driver of the UHI effect. Yet, additional sensitiv-
ity experiments with COSMO-CLM coupled to TERRA-URB clearly show that the impact of both the UF, the anthropogenic heat emission (AHE), and the synergy between those two impacts determine the seasonal depen-
dency of the UHI intensity. Remarkably, the averaged contribution of the UF to the nocturnal boundary-layer UHI for the cities in and around Belgium (+0.45 K for Brussels) during winter is smaller than that from the
AHE (+1.27 K). Conversely, the contribution of the UF (+1.97 K) dominates that of the AHE (+0.84 K) during summer. The respective contributions counteract each other during summer (-0.33K), whereas they slightly
enhance each other during winter (+0.15 K). Within the general assessment of global climate change projections, land-use change scenarios and urban climate mitigation, we recommend to account for each of these effects and
their implications at every season.