ИСТИНА

The Moscow megacity is the biggest monocentric agglomeration in Europe. Due to its size, location in a zone of continental climate and specific building features, such as the predominance of high-rise block-houses, Moscow forms an intensive urban heat island (UHI) with a mean annual intensity equal to 2 ⁰С with maximum values up to 12-13 ⁰С (Lokoschenko, 2014). All these features, in addition to the compact and relatively symmetric shape of the city and its location within a flat and homogeneous terrain makes Moscow a promising and interesting place for urban climate studies. Another reason making such researches especially important for Moscow is related to the trend of UHI intensification during the last decades, which leads the urban-induced enhancement of global warming (Kislov et al., 2017). For these reasons, further investigation of the drivers of the observed and expected urban climate changes becomes an important scientific problem. Since recently, it has become even more important for Moscow due to ambitious projects of the further city development, such as plans of the development of the so-called “New Moscow” area located to the south-west of the city, which was administratively joined to Moscow in 2011, and the program of renovation of old five-story buildings adopted in 2017 (according to it, more than 5000 buildings all over the city will be demolished and replaced by at least twice as high buildings). In this study, the experience of applying a regional mesoscale climate model COSMO-CLM (Böhm et al. 2006) to simulate the summer climate features of Moscow megacity is examined. The model was adapted to the conditions of the region under investigation (Varentsov et al., 2017), supplemented by specific urban canopy parameterization TERRA_URB (Wouters et al., 2016) and equipped with realistic parameters of urban surface, obtained with application of the original GIS-based technique (Samsonov et al., 2015). Numerical simulations were conducted for 10 summer seasons with 1 km horizontal grid step. It was possible to successfully simulate the summer meteorological regime of Moscow region and, specifically, the temporal and spatial variability of the Moscow urban heat island (UHI). The configured and verified model was used for the assessment of the summer climate responses to the implementation of different scenarios of the urban growth, assuming the doubling of the Moscow population. They included the quasi-isotropic urban expansion, building up the territory of "New Moscow" and intensive urban development within existing urban area (increasing the building height and density). The simulations for these scenarios show that the development of new urban areas or increasing the buildings height and density within existing ones leads not only to local effect on the temperature, but also to the amplification of urban mesoclimatic anomalies resulting in non-local effects. Partially, we show that development of the new urban areas on the periphery of the megacity (quasi-isotropic urban expansion) makes a heating impact on its central historical part (Figure 1a) and increases of the UHI effect, on the average, by 0.2 – 0.3K or by ≈10% in relation to its modern summer intensity for the city center. This explains observed trends of UHI intensification (Kislov et al., 2017). Moreover, the considered scenarios of city development enhance the positive urban-caused precipitation anomaly and increase its area. During the extreme heat events the temperature response to the considered scenarios is approximately twice stronger in comparison to summer-mean values (see example for quasi-isotropic urban expansion in the Figure 1b), which deteriorates human health and increases thermal stress. Partially, urban growth makes pronounced local and non-local effects on the frequency of so-called “hot nights” and unfavorable conditions in terms of the number of heat stress indices. Among the considered scenarios, the strongest effect on the temperature, precipitation and human comfort is caused by the development of new urban areas around the modern city or within its borders, while increment of the building height and density without extension of the urbanized area makes weaker impact on the urban climate. Acknowledgements: The research was supported by the grant program of Russian Science Foundation (project no. 17-77-20070 "An initial assessment and projection of the bioclimatic comfort in Russian cities in XXI century against the context of climate change") References: Böhm, U. et al., 2006. CLM—the climate version of LM: brief description and long-term applications. COSMO newsletter, 6, pp.225–235. Kislov, A. V. et al., 2017. “Heat island” of the Moscow agglomeration and the urban-induced amplification of global warming [in Russian]. Moscow University Vestnik. Series 5. Geography, 4, pp.12–19. Lokoshchenko, M.A., 2014. Urban “heat island” in Moscow. Urban Climate, 10, Part 3, pp.550–562. Samsonov, T.E., Konstantinov, P.I. & Varentsov, M.I., 2015. Object-oriented approach to urban canyon analysis and its applications in meteorological modeling. Urban Climate, 13, pp.122–139. Varentsov, M.I., Konstantinov, P.I. & Samsonov, T.E., 2017. Mesoscale modelling of the summer climate response of Moscow metropolitan area to urban expansion. IOP Conference Series: Earth and Environmental Science, 96, p.12009. Wouters, H. et al., 2016. Efficient urban canopy parametrization for atmospheric modelling: description and application with the COSMO-CLM model for a Belgian Summer. Geoscientific Model Development, 9, pp.3027–3054