Quantifying the Trends in Land Surface Temperature and Surface Urban Heat Island Intensity in Mediterranean Cities in View of Smart Urbanization

Abstract

Land Surface Temperature (LST) is a key parameter for the estimation of urban fluxes as well as for the assessment of the presence and strength of the surface urban heat island (SUHI). In an urban environment, LST depends on the way the city has been planned and developed over time. To this end, the estimation of LST needs adequate spatial and temporal data at the urban scale, especially with respect to land cover/land use. The present study is divided in two parts: at first, satellite data from MODIS-Terra 8-day product (MOD11A2) were used for the analysis of an eighteen-year time series (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017) of the LST spatial and temporal distribution in five major cities of the Mediterranean during the summer months. LST trends were retrieved and assessed for their statistical significance. Secondly, LST values and trends for each city were examined in relation to land cover characteristics and patterns in order to define the contribution of urban development and planning on LST; this information is important for the drafting of smart urbanization policies and measures. Results revealed (a) positive LST trends in the urban areas especially during nighttime ranging from +0.412 • K in Marseille to +0.923 • K in Cairo and (b) the SUHI has intensified during the last eighteen years especially during daytime in European Mediterranean cities, such as Rome (+0.332 • K) and Barcelona (+0.307 • K).Surface urban heat island (SUHI), in particular, describes the land surface temperature (LST) differences between urban areas and their surroundings, and it is usually studied with the use of remote sensing data. The formation of SUHI can be mainly attributed to the increased absorption and trapping of solar radiation in urban areas associated with limited release of heat due to the low values of the thermal emission coefficients of manmade materials. Anthropogenic heat release from transport and the heating-cooling systems of the buildings further exacerbate the phenomenon [18][19][20]. Both UHI and SUHI can be detected throughout the year, but they are of particular public policy concern during the summer, because higher surface and air temperatures are associated with increases in electricity demand for air conditioning, air pollution, and heat stress-related mortality and illness [21][22][23][24][25]. Several SUHI studies have been performed in the Mediterranean area, most of them revealing that higher UHI intensities are found in the summer period [13,[26][27][28][29][30].Land surface temperature is a controlling factor for most of the physical, chemical and biological processes on the earth, and can be considered as a measure of climate change [31][32][33][34]. For the urban environment, LST is an important parameter for the monitoring of the energy exchange between the land surface and the atmosphere in terms of the sensible and latent heat fluxes [35][36][37][38] which are important when discussing the thermal effects of the cities on th...

Time-Series Analysis Reveals Intensified Urban Heat Island Effects but without Significant Urban Warming

“…The Beijing metropolitan area had intensified SUHI, as suggested by the increasing trend of SUHII from 2000-2015. This result is consistent with that from a large amount of studies, which found that with urban expansion, the UHII (both SUHII and UHII in terms of air temperature) tends to increase [33,37,39,41,43,60,72,[76][77][78]. Compared to old urban areas (OUA in this study), the new urbanized and urbanizing areas (NUA in this study) had a more rapid intensification of UHI, which was indicated by both the SUHII and LST values, similarly to findings from previous results [34,42,60,79].…”

“…We then calculated the SUHII at the pixel level for each pixel in the UA, which was the difference between the LST of each pixel in the UA and the averaged LST in the NoUA. After we obtained the data of SUHII, LST, EVI, and NDBI from 2000 to 2015, we investigated the temporal trends of such variables (e.g., SUHII) at every pixel using ordinary least squares (OLS) linear regression models [36,43,72]. Here we use Trend LST as an example to illustrate the calculation of Trend LST, Trend SUHII , Trend EVI , and Trend NDBI .…”

“…Previous studies have shown that UHII increased along with urban expansion [32][33][34][35][36] in cities such as Beijing [37-40], Shanghai [41], Wuhan [42], and Lanzhou [22] and also in urban agglomerations [32,43]. A decrease in UHII was also observed in a few cities [33,34,44].…”

“…The UHII and its spatiotemporal variations are related to urban and rural characteristics, including biophysical and social attributes [10,[24][25][26][27][28][29]. For example, UHII had a strong negative relationship with the difference between the urban and rural vegetation indexes [10,25,27,[29][30][31], but a significantly positive relationship with urban-rural nighttime lights [26].Previous studies have shown that UHII increased along with urban expansion [32][33][34][35][36] in cities such as Beijing [37-40], Shanghai [41], Wuhan [42], and Lanzhou [22] and also in urban agglomerations [32,43]. A decrease in UHII was also observed in a few cities [33,34,44].…”

Medium-sized Cities in Spain and Their Urban Areas within National Network

“…The Mediterranean Corridor refers to the whole coastal strip that ties together the East of Iberian Peninsula through several transport infrastructures. The specific study of Mediterranean cities has previously preoccupied different scholars [61,62]. 53 medium-sized cities are located along the Mediterranean coast, in which more than five million people currently live.…”