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Abstract:The local climate in cities differs from the one in rural areas, most prominently characterized by increased surface and air temperatures, known as the "(surface) urban heat island". As climate has changed and continues to change in all areas of the world, the question arises whether the effects that are noticeable in urban areas are "homemade", or whether some of them originate from global and regional scale climate changes. Identifying the locally induced changes of urban meteorological parameters is especially relevant for the development of adaptation and mitigation measures. This study aims to distinguish global and regional climate change signals from those induced by urban land cover. Therefore, it provides a compilation of observed and projected climate changes, as well as urban influences on important meteorological parameters. It is concluded that evidence for climate change signals is found predominantly in air temperature. The effect of urban land cover on local climate can be detected for several meteorological parameters, which are air and surface temperature, humidity, and wind. The meteorology of urban areas is a mixture of signals in which the influencing parameters cannot be isolated, but can be assessed qualitatively. Blending interactions between local effects and regional changes are likely to occur.

The impact of urban areas on the global and regional climate has been assessed using the global Conformal Cubic Atmospheric Model (CCAM) including an urban canyon parameterization at a global resolution of 50 km. Simulations were produced with and without urban areas to assess urban impacts for the historical period 1980-2000. Two different land cover and urban datasets (one based on IGBP-DIS, the other on MODIS) were tested. In addition, simulations were performed for the end of the 21st century with the RCP8.5 scenario. Evaluation of the historical climate simulations indicates realistic local urban effects, such as higher daily minimum air temperatures (tasmin), higher sensible heat flux and lower latent heat flux at urban grid cells. In regions with large fractions of urban areas, some regional changes are also noted. In addition, there are significant regional effects far away from the main urban areas, which are similar in magnitude to the effects of the different non-urban land cover input datasets. Under the projected warming at the end of the 21st century (with no land cover change), there is a decrease in anthropogenic heating, primarily during wintertime. There is a slightly smaller increase in daily maximum temperature and a slightly larger increase in tasmin in urban areas compared to rural areas. This leads to a smaller increase in the diurnal temperature range within urban areas. The tasmin changes also imply an increase in the urban heat island effect for larger cities. The results of this sensitivity study show that there is a detectable impact of urban areas on high-resolution global climate simulations. Consequently, there is a need to include urban areas in global simulations, as well as in studies of land-use change. K E Y W O R D S climate, high resolution, numerical model, urban canyon model 1 INTRODUCTION Human activity affects the Earth's climate on different scales. The human-induced emissions of greenhouse gases (GHG) have already resulted in detectable global climate change, which is projected to intensify in the future (IPCC, 2013, 2019). In addition, due to the intentional and unintentional conversion of land cover (e.g., urbanization, deforestation and desertification) human activity has caused changes in physical properties such as albedo, soil This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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