Spatial patterns of the urban heat island in Zaragoza (Spain)

Abstract

Spatial patterns of the urban heat island (UHI) in Zaragoza (Spain) were determined by Principal Component Analysis (VARIMAX rotation) of air temperature in the city, and mapped using GIS. The 3 components extracted accounted for 92.9% of the total variance. Principal component (PC) 1 accounted for the most general patterns of UHI, PC2 showed a shift of warm areas to the SE and PC3 a shift to the NW. A rotated component matrix was used to identify correlations between each component and daily maps. The spatial patterns indicated by PC2 and PC3 were determined by surface wind direction. The displacement of warm areas to the SE (PC2) was greater during NW winds while the shift to the NW (PC3) was produced mainly by SE winds. KEY WORDS: Urban climate · Urban heat island · Spatial patterns · Principal component analysis · Surface wind · Zaragoza · SpainResale or republication not permitted without written consent of the publisher Clim Res 30: 61-69, 2005 wind direction. For these purposes we used urban transects, surface interpolation techniques and multivariate statistics of a Geographical Information System (GIS). STUDY AREAThe city of Zaragoza is located in NE Spain (Fig. 1) in the centre of the Ebro Valley (0°52' W, 41°38' N). It is the main industrial and commercial city of this region and occupies a plain of 159 km 2 ; in 2002 the city had a population of 620 000. It has a Mediterranean climate with a strong continental influence. The mean annual rainfall is just over 320 mm, with a maximum in May (38 mm) and minimum in August (21 mm). The mean annual temperature is 14.6°C, with cool winters (January: 6.2°C) and warm summers (July: 24.3°C). Winds are an important feature of the climate in the Ebro Valley. Two surrounding mountain ranges (the Pyrenees and the Iberian Range) isolate the valley from northerly and southerly flows, and winds are channeled in the valley in 4 dominant directions: WNW, NW, ESE, E. Westerly flows (W, WNW, NW, NNW) occur on 52% of the days, whereas ESE and E winds occur on 21% of the days.The UHI in Zaragoza has been studied by Cuadrat (1993), Cuadrat et al. (1993), De la Riva et al. (1997) and Saz et al. (2003). The absolute maximum difference in the temperature between the city and the outskirts is about 6°C, with a mean UHI intensity of 2.5 to 3.5°C. The UHI of Zaragoza shows a negative gradient from the city center to the outskirts, which is consistent with the findings of studies in other cities. Nevertheless, on many days the warm areas of Zaragoza present a marked shift to the NW or SE areas of the city. DATA AND METHODS Spatial variability of the UHI3.1.1. Data and quality control UHIs can be analyzed using urban-rural differences in the data from weather stations or groups of weather stations (i.e. Adeabayo 1987, Philandras et al. 1999; networks of fixed stations within and around the city (i.e. Kuttler et al. 1996, Morris et al. 2001; or, mainly, transects across an urban area (i.e. Moreno 1994, Saaroni et al. 2000, Unger et al. 2001.To determine the shape and tem...

Local regression models for spatial interpolation of urban heat island—an example from Wrocław, SW Poland

“…The method can be used to spatialize discrete point data on the assumption that auxiliary, independent variables are known and continuous in space, or, technically, they can be provided as raster layers. MLR has been successfully used for climatological purposes, as well as for UHI spatialization (Svensson et al 2002;Bottyán and Unger 2003;Vicente-Serrano et al 2005;Alcoforado and Andrade 2006;Szymanowski and Kryza 2009). Independent variables were selected for each UHI case from the set of potential predictors described in Section 4.1.…”

“…The first attempts to analyze the UHI structure were based on manually interpolated isotherm maps (Duckworth and Sandberg 1954). More sophisticated interpolation algorithms became popular with the increasing access to effective computers and development of geographic information system (GIS) (Svensson et al 2002;Bottyán and Unger 2003;Vicente-Serrano et al 2005;Alcoforado and Andrade 2006). Most of the recent studies on spatial characteristic of UHI are based on multidimensional interpolation algorithms, with the multiple linear regression (MLR) being the most often applied (Unger et al 2010).…”

GIS-based techniques for urban heat island spatialization

“…Detailed information on interpolation techniques applied was not included in these previous papers and only a few studies were supported by more advanced mathematical tools (PrestonWhyte 1970, Clarke & Peterson 1973. The development of GIS gave rise to a number of papers dealing with spatialization techniques and the UHI spatial structure (Svensson et al 2002, Bottyán & Unger 2003, Szymanowski 2004, Vicente-Serrano et al 2005, Alcoforado & Andrade 2006. Nowadays, computationally demanding methods are available and, more importantly, development of continuous information on potential UHI predictors, and sine qua non conditions for the use of multidimensional spatialization techniques, is feasible.…”

“…Nowadays, computationally demanding methods are available and, more importantly, development of continuous information on potential UHI predictors, and sine qua non conditions for the use of multidimensional spatialization techniques, is feasible. Svensson et al (2002), Vicente-Serrano et al (2005), and Alcoforado & Andrade (2006) present the results of UHI spatialization using different environmental (climate and terrain) information as potential predictors. The 'urban' group of UHI predictors used in spatial interpolation is related to various features characteristic of the urban environment (Bottyán & Unger 2003, Szymanowski 2004, Szymanowski & Kryza 2006.…”

A Linear Model for Moving Measurements Estimation in Urban Climate Studies

“…More specifically, the mobile measurement method (Charabi and Bakhit, 2011;Murphy et al, 2007). Vicente-Serrano et al, 2005) is usually used to obtain a detailed horizontal distribution of climate variables. The methodology begins with the specification of the urban area under study and the points inside this area where the measurements will take place.…”