The shape and magnitude of Porto's heat island as a sustainability indicator

Ana Monteiro, Helena Madureira, The shape and magnitude of Porto’s heat island, 45 th ISOCARP Congress 2009 1 The shape and magnitude of Porto’s heat island as a sustainability indicator 1. Introduction One of the most often used arguments to promote low carbon cities has been the need to adapt urban areas to global warming. This is, in our opinion, a precarious and unsteady option because drives us into a complex and endless controversy about the real value of human actions on climate behaviour at a global scale and push us away from the needed solutions to solve the real problems that affects the quality of the air we breathe and the climate of the place where we live. While the importance of human activities in the global climate system is still unknown for sure because climate has a chaotic performance and an imprecise time lag response, the local relationships between human activities and the microclimate are easy to demonstrate and understand looking, for instance, to the impacts in the atmospheric chemistry and energy budget. Therefore, the appeal to create low carbon cities excessively anchored in the global warming threats can be severe weakened and even fail because people – citizens and decision makers – will, with some legitimacy, expect to see the effects of their new attitudes and actions on climate answers, and, they may not come as they expect. So, if we want to improve our urban ecosystems’ sustainability and at the same time discourage the inputs of large amounts of greenhouse gases in the atmosphere to avoid some potential undesirable answers from the climate system, we must try to downscale this issue using local and regional cause-effect relationships. At this scale level, the climate behaviour’ mechanics is much more clear and easier to verify. The urban heat island might be a good option to motivate the implementation of low carbon cities because it is a steady evidence of human interference in climate system. The identification of causes – gaseous and liquid emissions, waste, new geometries, new materials, decrease of green areas, large and very inefficient energy consumption, etc. – and consequences - thermal positive anomalies, rainfall changes, wind modification, atmospheric pollution, etc. – is easy to do at the local and regional level. The shape and magnitude of urban thermal anomalies due to urban lifestyle and planning options are indeed excellent indicators of some of the major cities’ pathologies, namely the huge increase of CO emissions. Since Luke Howard’s studies of London urban climate, published in 1818, there have been an extraordinary number of works done in urban areas that express clearly how the urban metabolism matters to local climate. One of the main key issues tackled, in some of these studies, is precisely the air quality degradation generated by several human activities and by the way atmospheric circulation is changed because of the new artificial geometries or even by the decrease of CO sink capacity (less water surfaces, green areas, etc.). At Porto, we have already data of thermal and humidity measurements inside the metropolitan area since 1990, and the achieved results might help to explain better how we need, as individuals and as society, to implement a fast shifting towards a low carbon way of life. Ana Monteiro, Helena Madureira, The shape and magnitude of Porto’s heat island, 45 th ISOCARP Congress 2009 2 One of the most obvious examples of new imbalances created by man during the urbanization process may be seen in our city looking to the way how it assisted at the same time to a carbon emissions increase due to the diversification and increase of human activities and, simultaneously, to a considerable contraction of CO sinking capacity because of the green areas removal. This double and cumulative stress upon atmosphere is a decision makers’ and urban planners’ responsibility because they ignored nature complexity and failed to have holistic and systemic approach to the urban ecosystem. 2. Porto case study 2.1. The spread of urban life style All population’s projections show that human beings, despite everything, will continue to prefer living in urban areas than in rural ones. This will be particularly evident in less developed countries which may mean an enormous imbalance increase between the size and location of the available space, resources and people needs (Fig. 1). Since 2003 till 2030 the urban population in the world is expected to rise from 3 billion to 5 billion while the rural population is expected to decrease, in the same lag of time, from 3.3 billion to 3.2 billion (Fig. 1). Fig. 1 – UNPD Population projection (2007). Since 2007, the world has, for the first time in history, more urban than rural inhabitants and according to UNPD projections the annual rate will raise 1.8% what means an expected doubling in a 40 years period. For the time being one of the major apprehensions comes precisely from the way this lifestyle have spread at an extremely high rate in developing countries where the growth of urbanization started in 1970 with a population increase rate that was the double of the rural. In Africa, for instance, the rate overpasses the 4.5% per year - a doubling in an interval of 15 years. This urban growth process changed completely the social, economic and man-environment relationships. The complexity and intensity of the territorial and social multidimensional sculpture created by this new lifestyle generated an imbalance between people needs and available natural resources that carried entirely new faces on earth. 0 1000000 2000000 3000000 4000000 5000000 6000000 7000000 8000000 9000000 10000000 Nº (thousands) Total population Total population More Developed Countries Total population Less Developed Countries Ana Monteiro, Helena Madureira, The shape and magnitude of Porto’s heat island, 45 th ISOCARP Congress 2009 3 2.2. Porto’s urbanization process Portugal follows the EU urban growth rate trend with considerably higher values (Fig. 2). However, Lisbon and Porto, the two major Portuguese cities show, as in all EU, a decrease in urban growth rate after the 80’s (Fig.3). Fig.2 – UNDP urban growth rate projections (2007). Fig. 3 – Porto’s site and geographical position. Fig.3 – UNDP urban growth rate projections to Lisbon and Porto (2007). Porto is the second most important town in Portugal and is situated inside a metropolitan area (GAMP - Porto Metropolitan Area) with 1 281 424 inhabitants, located in the NW coast of Iberian Peninsula (Fig. 4 and 5). In 2005, Porto had 233 465 inhabitants. It is a city with a daily flux of more than 500 000 persons. It concentrates mainly services – administrative, educational and cultural – and offers more than 218 000 jobs. About 50% of the employees come from nearby municipalities using public and private transports. Porto had an enormous economic growth during the three last decades. Especially after becoming membership of the EU, in 1986, Portugal has constantly benefited from significant amounts of EU funds in order to create and/or renew its productive tissue, infrastructures and human resources qualifications. During this period we assist, in Porto, at a considerable 0 0,5 1 1,5 2 2,5 3 3,5 19501955 19551960 19601965 19651970 19701975 19751980 19801985 19851990 19901995 19952000 20002005 20052010 20102015 20152020 20202025 Average annual rat e(%) Lisbon Porto Ana Monteiro, Helena Madureira, The shape and magnitude of Porto’s heat island, 45 th ISOCARP Congress 2009 4 change in industrial and commercial location patterns and in accessibility networks. This was closely followed by great changes in behaviour and mentalities. These new economic period of hope and prosperity, translated by an increase in the family incomes, carried also a great temptation to survive in a wild competition inside an enlarged and more appellative market, which unfortunately led also some negligent attitudes towards all the environmental components (eg. air, water, soil, etc.). Fig. 4 – Site and geographical position of Porto. Fig. 5 - Porto Metropolitan Area (GAMP). Ana Monteiro, Helena Madureira, The shape and magnitude of Porto’s heat island, 45 th ISOCARP Congress 2009 5 If to all this we add the fact that these last three decades has been a time of tremendous progress in the scientific and technological innovation, it is explained the belief that it was possible to replicate any urban model regardless each geographical specificity. The conviction was that everything could be solved with creativity, science, technology and extra inputs of energy. Porto has several urban planning evidences of this way of urban planning at that time. Porto’s population evolution was, until the 80’s, very similar to the rhythm of its metropolitan area (GAMP). After this decade, while Porto’s population decreases, its metropolitan area experienced a population increment (Fig. 6 to 9). The demographic regression of Porto along the last decade of the 20th century happened mainly because of the huge housing decentralization, as well as to an enormous fall on the birth rates. Fig. 6 – Porto’s inhabitants (INE, 1884-2001). Fig. 7 – Porto population density (INE, 2001). Ana Monteiro, Helena Madureira, The shape and magnitude of Porto’s heat island, 45 th ISOCARP Congress 2009 6 Fig. 8 – Buildings constructed before 1919 (INE, 2001) Fig. 9 – Buildings constructed after 1996 (INE, 2001). Porto’s population drainage process, mostly towards the GAMP’s nearby municipalities, and the births drop was accompanied by structural changes in family type and in the age pyramid distribution. The average family size diminished and the number of single parent families augmented as well as the number of lonely elderly people increased. The CMP’s mobility report (2007) confirm the high expression of individual movements in the city of Oporto daily traffic - a total of 93 thousand travels by car registered between 7:30 a.m. and 9:30 a.m (Fig. 10 to 12). 30 thousand of the totals 42 thousand motor vehicles circulating inside the city go to the central urban area, especially to the old town – Baixa – Boavista roundabout and Asprela (CMP, 2007). Fig. 10 – Cross-city traffic between 7.30-9.30 am (CMP, 2007, pg.7). Ana Monteiro, Helena Madureira, The shape and magnitude of Porto’s heat island, 45 th ISOCARP Congress 2009 7 Fig. 11 – Ratio in-out traffic between 7.30-9.30 am (CMP, 2007, pg.17). As Madureira (2001) showed in her research, the comparison of green surface shape and area between 1890 and 2001, clearly expresses the sustainability of the development and urban planning options (Fig. 12). Fig. 12 - Porto’s green areas in 1890 and 2000 (Madureira, 2001). Ana Monteiro, Helena Madureira, The shape and magnitude of Porto’s heat island, 45 th ISOCARP Congress 2009 8 3. The urban heat island in Porto (1990-2005) versus carbon emission and sink capacity estimations 3.1. Methodology to define the urban heat island To evaluate the thermal anomalies inside Porto we have done itinerant measurements in a validated transect whose star shape allow several points of data validation (Fig.13). Norte ponto de medição 0 500m Fig.13 – Porto’s itinerant measurements routing (1990-2005). The chosen route reflects a wide range of urban facies – topography, morphology and metabolism. It includes most of the higher altitudes and lower areas, it comprises places far away from the sea and the closest ones. Tries to cross districts are of great built compactness and the more recent residential blocks with high and spaced housing areas at the same time that goes through areas of great promiscuity of use. The route has also samples of different urban functions - industrial, commercial and residential. The data acquisition was made with a Delta OHM-HD 8501 digital thermohigrometer installed on the right side of the car roof of passengers’ vehicle at the height of about 1.5 m. The time lag between the beginning and end of the route – 70-80 minutes - prevented us from using, directly, the temperature values recorded. We standardized the obtained data series calculating the difference between each record and the simultaneously recorded value at the climatological reference station of Porto Serra do Pilar. This route was repeatedly done under different weather conditions, weekdays and seasons. There were also done some measurements using the same data acquisition procedures inside specific areas inside Porto – Asprela, Cordoaria, Sé – and in the nearby municipalities – Matosinhos, Srª Hora, Espinho, S.João da Madeira – that confirm the results obtained in these route (Gois, Balkestbal,) 3.1. Methodology to define carbon emission and sink capacity To estimate the CO 2 emissions we used the data compiled by the Carbon Dioxide Information Analysis Center, witch indicates the annual CO 2 emissions from fossil per country. The Porto CO 2 emissions from fossil-fuel were calculated proportionally to its population at each census date. Ana Monteiro, Helena Madureira, The shape and magnitude of Porto’s heat island, 45 th ISOCARP Congress 2009 9 To estimate the city sink capacity we used de CityGreen method, developed by the US Forest Service, which calculates the amount of carbon stored in the trees represented on the land cover map and calculates the annual carbon removal by the trees. CITYgreen defines three distribution categories based on the diameter of the tree, witch are associated with a certain multiplier: Carbon Storage Capacity = Study area in acres x Percent tree cover x Carbon Storage Multiplier Carbon Sequestration Annual Rate = Study area in acres x Percent tree cover x Carbon Sequestration Multiplier In the absence of precise data on tree age distribution, we used an average multiplier 3.2. Results 3.2.1.Shape and magnitude of the Porto’s urban heat island Before any further comment about the average nocturnal urban heat island found in Porto (Fig. 14), we must remember that the city is divided into two distinct areas, the western part, lower and plan, and the east, with higher altitudes and more rugged. We must also keep in mind that the Douro riverside slopes are steep and that it is to this area of the city that converge most of the streets, with a NNE-SSW orientation, that go to the oldest and historic city centre. These old town road networks have been drawn between great granite and tall buildings blocks that make very difficult the entrance of sunlight till the lower floors of buildings whatever the exposure. Fig. 14 – Average nocturnal urban heat island at Porto (Monteiro, 1993). The east area of the city corresponded to the rural ring at the beginning of the 20 th century and, since then, suffered an enormous increase in the occupation density. The buildings are usually lower, but in the interior, the space is completely filled by “ilhas” – an answer to the lack of housing for the lower socio-economic classes who immigrated to the city in the middle of the 20 th century. The western area was occupied most recently and has a large number of new neighbourhoods, where individual houses and / or large blocks of flats have been emerging over wide avenues.