Urban Imperviousness Effects on Summer Surface Temperatures Nearby Residential Buildings in Different Urban Zones of Parma

Marco Morabito, Alfonso Crisci, Teodoro Georgiadis, Simone Orlandini, Michele Munafò, Luca Congedo, Patrizia Rota, Michele Zazzi
2017 Remote Sensing  
Rapid and unplanned urban growth is responsible for the continuous conversion of green or generally natural spaces into artificial surfaces. The high degree of imperviousness modifies the urban microclimate and no studies have quantified its influence on the surface temperature (ST) nearby residential building. This topic represents the aim of this study carried out during summer in different urban zones (densely urbanized or park/rural areas) of Parma (Northern Italy). Daytime and nighttime
more » ... me and nighttime ASTER images, the local urban cartography and the Italian imperviousness databases were used. A reproducible/replicable framework was implemented named "Building Thermal Functional Area" (BTFA) useful to lead building-proxy thermal analyses by using remote sensing data. For each residential building (n = 8898), the BTFA was assessed and the correspondent ASTER-LST value (ST_BTFA) and the imperviousness density were calculated. Both daytime and nighttime ST_BTFA significantly (p < 0.001) increased when high levels of imperviousness density surrounded the residential buildings. These relationships were mostly consistent during daytime and in densely urbanized areas. ST_BTFA differences between urban and park/rural areas were higher during nighttime (above 1 • C) than daytime (about 0.5 • C). These results could help to identify "urban thermal Hot-Spots" that would benefit most from mitigation actions. Remote Sens. 2018, 10, 26 2 of 17 continuous conversion of green, or generally other natural spaces, into artificial surfaces (soil sealing or imperviousness). This last phenomenon is defined as the permanent covering of soil by completely or partly impermeable artificial materials (e.g., asphalt, concrete, and brick) [2] . Imperviousness is the main cause of soil degradation in Europe [3] . It contributes to the progressive and systematic destruction of the natural landscape, increasing the risk of flooding (due to the water runoff rising) and water scarcity, and strengthens the climate change magnitude (influencing the carbon cycle). Moreover, it threatens the biodiversity (reducing or affecting habitats), causing a loss of fertile agricultural land and natural and semi-natural areas [4] . In particular, as urban settlements have been historically established next to the most fertile areas, soil sealing often affect the most fertile soils, in this way affecting European food security [2] . Urban areas are characterized by the highest degree of imperviousness and continuous built-up areas [5] with direct consequences on its microclimate. The high thermal conductivity and the heat storage capacity, often coupled with low solar reflectivity of most artificial impervious surfaces, cause alterations to the energy budget of the surfaces, increasing the sensible heat instead of the latent heat, and producing a generalized rise in the urban temperature. This situation significantly contributes to the well-known urban heat island (UHI) effect, represented by local surface and air temperatures in densely built-up city areas consistently higher than the temperatures observed in surrounding rural landscapes characterized by a greater density of pervious surfaces [6] . This phenomenon tends to create many critical conditions in the urban environment, among which the amplification of the urban heat load during summer heat-wave events [7,8] and significant increases of housing cooling loads and electricity consumption [9,10], are potential causes of harmful blackouts or brownouts. This situation is also associated with an exacerbation of thermal discomfort [11] and the higher levels of heat-related-mortality of vulnerable people living in densely built-up districts of urban areas than rural ones [12] . In urban thermal environment studies, the land surface temperature (LST) estimated by thermal infrared remote sensing techniques draws more attention than the air temperature measured by local meteorological stations for several reasons. Meteorological station networks allow discrete and generally scattered monitoring (often in suburban areas) representative of areas with determined physical characteristics, which hardly reflect the spatial air-temperature variation based on different surfaces that characterize the heterogeneous urban/suburban environments [13] . Then, thermal infrared remote sensing data have been extensively used in urban climate studies for analyzing the LST patterns and its association with built-up indicators [14] [15] [16] [17] [18] [19] . The introduction of very high spatial resolution satellite images (i.e., IKONOS, Quickbird, and RapidEye) and more efficient image processing techniques implemented by GIS software tools have allowed the development of advanced technologies for better mapping and quantifying urban impervious surfaces [20] [21] [22] [23] [24] [25] . A representative example in this context at European level is the Copernicus program (coordinated and managed by the European Commission with the fundamental contribution of the European Space Agency and the European Environmental Agency) that includes the acquisition of data from multiple satellites and the integration with field surveys (in situ data and services). Copernicus ensures the homogeneity of environmental monitoring in general, and in particular the land cover classification at European level [26] . As part of the Copernicus framework, several high-resolution layers were produced for specific purposes at the national level, with 2012, 2015 and 2016 as reference years. As an example, the Italian National Institute for Environmental Protection and Research (ISPRA: Istituto Superiore per la Protezione e la Ricerca Ambientale) developed very high-resolution maps of built-up surfaces (a binary indicator of urbanization) for the entire Italian territory [27, 28] . These data were used in a recent study [29] to evaluate the relationships between built-up-surface densities and daily LST (daytime and nighttime) in several Italian cities. Modeling these relationships, useful urban maps have been developed visualizing the spatial footprint of imperviousness on urban microclimate. However, the easy access to remote sensed resources, coupled with a wider coverage and better spatial resolution of thermal infrared measurements, would allow more detailed urban analyses, as well as investigating the situation nearby buildings. Currently,
doi:10.3390/rs10010026 fatcat:tyzboea6nzbo3mhezzhkylpari