Long-Term Impact of Urban Areas on Meteorological Conditions Over Central Europe.

The impact of urban areas on relevant meteorological variables, especially on temperature and wind speed, is well-known, and several studies have evaluated this effect. However, fewer of them have focused on the effect of urban areas on cloud cover and precipitation. To evaluate this, a total of 15 simulations were performed using the Weather Research and Forecasting model on a Central European domain at 9-km horizontal resolution. The novelty of this study is the number of cities considered and ensembles used over a 10-year period including not only the impacts of the urban scheme but also the effects of two other relevant parameterizations, namely, convection and microphysics, on the representation of the urban meteorology island (UMI) variables with a special focus on less studied variables, that is, cloud cover and precipitation. Our results show that changes in temperature and specific humidity are mostly sensitive to the urban scheme selected, while changes in precipitation and cloud cover are more sensitive to the parameterization of convection and microphysics. The cloud cover strongly depends on the convection and microphysics schemes, especially in summer (JJA), although the impacts of the different parameterizations depend on the selected city. Despite differences observed among cities, cloud cover increases over urban areas during the afternoon and evening and decreases during the morning and night, especially in JJA. The selection of both convection and microphysics schemes plays an important role in the simulated precipitation. In winter (DJF), no significant variation between simulations is observed. On the other hand, precipitation is enhanced over urban areas during JJA. This study highlights the importance of using model ensembles and a number of cities when evaluating the urban heat island and UMI meteorological values, as large differences exist between the different setups and selected cities.