Abstract
Abstract. Cities and urban areas are well-known for their impact on meteorological variables and thereby modification of the local climate. Our study aims to generalize the urban-induced changes in specific meteorological variables by introducing a single phenomenon – the urban meteorology island (UMI). A wide ensemble of 24 model simulations with the Weather Research and Forecasting (WRF) regional climate model and the Regional Climate Model (RegCM) on a European domain with 9 km horizontal resolution were performed to investigate various urban-induced modifications as individual components of the UMI. The results show that such an approach is meaningful, because in nearly all meteorological variables considered, statistically significant changes occur in cities. Besides previously documented urban-induced changes in temperature, wind speed and boundary-layer height, the study is also focused on changes in cloud cover, precipitation and humidity. An increase in cloud cover in cities, together with a higher amount of sub-grid-scale precipitation, is detected on summer afternoons. Specific humidity is significantly lower in cities. Further, the study shows that different models and parameterizations can have a strong impact on discussed components of the UMI. Multi-layer urban schemes with anthropogenic heat considered increase winter temperatures by more than 2 ∘C and reduce wind speed more strongly than other urban models. The selection of the planetary-boundary-layer scheme also influences the urban wind speed reduction, as well as the boundary-layer height, to the greatest extent. Finally, urban changes in cloud cover and precipitation are mostly sensitive to the parameterization of convection.
Highlights
Climate is one of the most important factors that influences the conditions for life at a specific place
Our study aims to generalize the urban-induced changes in specific meteorological variables by introducing a single phenomenon – the urban meteorology island (UMI)
The temperature underestimation of Weather Research and Forecasting (WRF) simulations with the MYJ planetary boundary layer (PBL) and Eta surface layer (SFL) schemes (Fig. 3) in the winter season is similar to that detected by Karlický et al (2018); summer temperatures are probably influenced by the Tiedtke convection scheme (Tiedtke, 1989), which is not tested in this study but makes a smaller summer overestimation of precipitation, related to higher summer temperatures
Summary
Climate is one of the most important factors that influences the conditions for life at a specific place. Considering the fact that half of the current global population lives in cities (United Nations, Department of Economic and Social Affairs, 2014) and the populations of the largest cities are still projected to increase (Baklanov et al, 2016) and that the total number of cities of different sizes is rising (Mirzaei, 2015), general knowledge of typical urban climate features and the difference with respect to their rural counterparts is becoming more and more crucial. The most well-known urban climate feature is the socalled urban heat island (UHI), first described several decades ago (Oke and Maxwell, 1975), and means, in simple terms, that urban temperatures are higher compared to rural ones. Specialized models of urban canopies within standard numerical weather prediction and regional climate models have been used to capture the specifics of urban climate features
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