On the urban heat island effects under extreme weather conditions – heat waves

Abstract:

As the most of population is living in the cities and the numbers are increasing, we need proper description of urban processes for proper assessment of impacts within the cities and of the effectiveness of adaptation and mitigation options applied in cities in connection with climate change as well as the urban heat island itself. To assess the impact of cities and urban structures on weather, climate and air-quality, modelling approach is commonly used and the inclusion of urban parameterization in land-surface interactions is of primary importance to capture the urban effects properly. This is especially important when going to higher resolution, which is common trend in operational weather forecast, air-quality prediction as well as regional climate modeling. Thus, it is valid not only for e.g. extreme heat waves impact prediction, but in air-quality prediction and long term perspective in connection to climate change impacts as well. This provides the background for the project within Operational Program Prague - The Pole of Growth “Urbanization of weather forecast, air-quality and climate scenarios for Prague”, shortly URBI PRAGENSI.

We demonstrate the importance of urban parameterization in regional simulations comparing WRF and RegCM with different urban parameterization options in 10 km resolution. There are differences in the impacts depending on the method, but basically all are able to capture the effects of urban heat island in these simulations, which can be quite significant especially under heat waves and achieve up to about 8-10 °C difference between the city and its vicinity for large urban areas during the night time. More detailed analysis of the effects in terms of energy balance in the city and remote areas in high resolution simulations will be presented. Experiments in convection permitting resolution of 3 km will be compared, resolving the city details and showing the urban heat island effects under extreme weather condition – heat waves.