Measurements and Modelization of the Rosario City Heat Island, Argentina - Preliminary Results

Abstract

In relation to climate, cities introduce a perturbation with respect to the adjacent (non-urban) lands, since houses, buildings, industries, streets, among others, are made of materials that usually have different optical and thermal properties. In particular, they storage heat in a larger fraction than bare land. Consequently, it is of interest to analyse the main variable that can characterize this difference, the ambient temperature. We present results of the measurements done with a thermometer (with an estimated maximum uncertainty of 0.2ºC) during the period June 2013 – June 2014, in different months of the year with clear sky and non-intense windy climatic conditions. The data were obtained at noon (around 13:00 local hour = Universal Time – 3 hours), traversing the city in the East-West and North-South directions. Particularly, in this work, we analyse the ambient temperature variation between the central dry Montenegro plaza and the Green Urquiza park. The first one is located among medium-height buildings (3 stories as a mean), while the second one is placed about 1770 meters away, in the border of the city, very near the coast of the large Paraná river (having it 60 km wide, including the delta islands). The mean temperature difference in the yearly investigated period was +0.7ºC, being higher in the central dry plaza than in the green park. Results for different climatic periods are: for autumn-winter, +0.3ºC and for spring-summer, +1.1ºC. A possible explanation of this behaviour is the different angular incidence of solar radiation at the altitudinal level that air temperature is measured, being lower in autumn-winter (with the Sun at approximately 40º mean elevation angle) than in spring-summer (∿70º mean elevation angle). We have also made model calculations, employing the Urban Weather Generator (UWG) model, developed by Bueno et al. at Massachusetts Institute of Technology, USA. As for the introduction of the climatological and building parameters, we have used climatological data from a rural meteorological station in the Energy Plus weather file format (.epw) and a parametric description of urban area in .xml format. We have also obtained a representation of the temperature behaviour in the central plaza, considering three scenarios. Scenario A represents the rural climate; scenario B portrays the current situation and scenario C verifies the Energy efficiency and solar protection in building N° 8757 Ordinance introduced for the first time in Argentina, by the Municipality of Rosario city. The highest temperature was found in scenario B, being 2.5 ºC higher than in scenario A. Scenario C presents a temperature 1.5 ºC higher than scenario A. In conclusion, the urban heat island data obtained is of interest in the design of acclimatisation systems (since normally the non-urban airport temperature data is employed). Also, they can be used as a simulation at present of what will happen in the future, due to the temperature increase produced by the emission of greenhouse gases, responsible of the global warming.