Abstract
It is already a well-known fact that air-temperature is the most important climatic factor of differentiation between intra- and extra-urban areas, mainly due to the characteristics of the underlying active surface. Bucharest town-area is no exception to the rule. Ranking as Romania’s largest city, its air-temperature singularities and differences account for the most important example expressing the role that the artificial ground layer may play in the creation of specific urban climates. The thermal differences as well as singularities between the Bucharest town-area (Bucharest-Filaret) and its surroundings (Bucharest-Băneasa) are analyzed by means of multiple air-temperature parameters: hourly measurements (01, 07, 13 and 19 hrs.), daily, monthly, yearly values of maximum, average and minimum means, over a 30 year period (1981-2010). Besides, the analysis of some air-temperature singularities or records highlight the clear differences of air heating processes, mostly due to the different interaction patterns between solar radiation and the underlying active layer, at local scales. However, in general, although the intra-urban areas should keep warmer in summer and cooler in winter, the cooling effects seem to still remain lower in the city because of the greater artificial heat input that is being added to the built-in environment.
Highlights
Urbanization, which mainly resulted in an intensive spatial concentration of population, dense built-in areas with impervious pavements, multiplied and vertically-differentiated layers of active surfaces, as well as scarcer green infrastructures, is obviously exacerbating any urban climate environment, by64 Ionac Nicoleta, Uriţescu Bogdan, Grigore Elena, Constantin Dana Maria, Dumitrescu A.largely altering the proportion between the urban heat island (UHI) effect, specific of the urban artificial landscapes, and the urban cool island (UCI) effect, characteristic of the green, vegetated spaces and bodies of water sparsely distributed inside the city area or in its surroundings (Chen A. et al, 2014)
Most recent studies have shown that the urbanization effect accounts for a large proportion of the overall annual mean surface air-temperature (SAT) increase at intra-urban meteorological stations, as well as for some significant changing trends of local and regional annual mean SAT values (Bian Tao et al, 2014), enhancing the UHI effect that may disturb the frequency and intensity of extreme temperature events, mostly addressing to the increase of both maximum (Tmax) and minimum (Tmin) air-temperature values over highly variable patch – patterns, as result of different interactions between the radiation processes and the properties of the underlying active surface
Relatively few studies have discussed the overall effect of urbanized areas on their surrounding air-environment, as expressed by their compact UHI effect, based on airtemperature values provided by ground-level meteorological stations, partly because relevant comparative intra- and extra-urban stations were either not available or they did not provide reliable data series under relatively characteristic metadata conditions
Summary
Urbanization, which mainly resulted in an intensive spatial concentration of population, dense built-in areas with impervious pavements, multiplied and vertically-differentiated layers of active surfaces, as well as scarcer green infrastructures, is obviously exacerbating any urban climate environment, by. The infra-red energetic input from artificial urban surfaces, traffic and indoor heating leads to some important changes in temperatures inside town areas, so that the concept of UHI has been introduced to denote the thermal difference between the urban builtin spaces and the surrounding open-space environments of cities (Cheval &Dumitrescu, 2014) For this reason, air-temperatures measured at intra-urban stations are usually higher than those obtained from surrounding rural stations in any season, but they become more obvious during summer, when the additional heat radiated by buildings amplifies the natural warming process of air inside town-areas. The present paper discusses the impact of the urban underlying surface on the time range and distribution of air-temperatures in Bucharest town area, based on the comparative values recorded at two different (intra- and extra-urban) meteorological stations, assessing both the intensity and the time gap of the heating and/or cooling processes inside the city
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