Ilha de calor urbana e sua influência na microfísica de nuvens em metrópoles brasileiras

Abstract

Urban areas modify the surface energy balance, leading to greater heat accumulation, with the consequence, compared to the surrounding areas of an increase in air and surface temperature values. This condition is described by the urban heat island (UHI) phenomenon, which, in recent years, has been further investigated by different fields. This phenomenon affects the population’s health, energy consumption, among other strategic areas. In Brazil, the intense urbanization has direct effects on the intensity of the phenomenon, which increases the mortality risks from heat-related diseases, besides the increase in energy consumption, among other impacts. Given this context, a concern arose to know in detail about the presence and effects of the UHI phenomenon in large Brazilian metropolises and whether there is an influence of urban overheating on the characteristics of precipitation and microphysical properties of clouds in the urban areas. To allow this understanding, methodologies applied to active and passive remote sensing data were used, together with statistical studies, which allowed to understand the effects of the UHI in different metropolitan regions and their relationships with other environmental variables (surface albedo and NDVI), analyzing UHI trends over 17 years (2000-2016) and the similarities between metropolitan regions, from statistical tests such as: Mann Kendall, Theil-Sen, t-Student (t paired). Our results indicate that all 21 metropolitan regions studied present heat islands, both diurnal and nocturnal and that of this total, 10 showed a positive trend in diurnal UHI values, which may be related to 2 different biophysical factors investigated, NDVI and surface albedo. Of these 21 studied regions, Manaus was the metropolitan region with the largest diurnal heat island recorded, besides its homogeneous surrounding with rain forest cover, because of this it was selected to evaluate the microphysical properties of urban clouds. The Ice Water Path (IWP), Rain Water Path (RWP), Convective Rain and Surface Rain properties were analyzed during the dry season in the Manaus metropolitan region for a period of 15 years (2000-2014). The results indicated that during the studied period, the urban convective precipitation rates were always higher at any time, however, with variations in the IWP and RWP concentrations, according to the time of day. With relation to the spatial-temporal distribution in the diurnal cycle, it was evident that the precipitation and other microphysical properties of the clouds are modulated by local circulation, in particular, by the action of river breeze. During the dawn, the highest values of all the microphysical properties studied are on the river, while in the afternoon these results occur on the banks. In this context, the presence of higher temperatures in Brazilian metropolises during the dry season, that possibly, a change in the pattern of cloud cover and precipitation (convective and surface) on the urban area and surroundings, which aggravates the impacts of heat on urban inhabitants and exposes the urban surface to receive a greater load of radiation.