Abstract
Abstract Climatic Evaluation For Urban Planning in Lisbon Climate is one element of the urban physical environment and an important component in improving sustainability of cities and the quality of urban life. However climatic quality it is not often taken into account in urban planning (Oke, 1984, 2005; Eliasson, 2000; Mills 2005) and there is hardly any legislation on climate effects in cities. The initial research that lead to these results was carried out in the frame of the CLIMLIS project: Prescription of climatic principles in urban planning. Application to Lisbon (POCTI/34683/GEO/2000), whose main goals were to increase knowledge of urban climate in Lisbon, to foresee the changes that will result from the process of urbanisation and also to suggest solutions in order to reduce the negative local effects of built-up areas. The City Council (Câmara Municipal de Lisboa, CML) became increasingly interested in our research and financed another small project (CML Project) to “spatialise” guidelines for planning on maps at different scales. The present report includes some of the results of the CML project, developed by a group of researchers of the Centro de Estudos Geográficos (CEG) of the University of Lisbon (Urban Climatology Team; Geo-ecology Research Area) and the Lisbon’s City Council. The main objective of the CML project was to “translate” knowledge of Lisbon’s urban climate into simple guidelines for urban planning in order to mitigate the urban heat island, promote ventilation and increase air quality. In the first stage of the project the main climatic problems of Lisbon were detected. They are related with the urban heat island, wind and air quality. This work was based on previous and present observational studies and modelling (Alcoforado, 1992b; Andrade, 2003; Lopes, 2002 and 2003; Alcoforado and Andrade, 2005; Andrade and Alcoforado, accepted; Vasconcelos et al., 2004, among others). Particular attention was given to green spaces (Andrade and Vieira, 2005). Temperature and humidity sensors were used for data acquisition in a network that includes 12 fixed stations equipped with data-loggers in sites with high sky view factors (>0.65), which are as free as possible of microclimatic influence of buildings and vegetation. Different models were used to estimate wind speed and mean radiant temperature (Envi-met, Rayman, WAsP) and the different terms of the energy balance were modelled. The Lisbon urban heat island (UHI) has an average intensity of 3ºC: the highest air temperatures occur mostly in the more densely constructed areas near the Tagus river bank and along the main circulation axis where there is ongoing construction. In areas of contrasting thermal seasons such as Lisbon, UHI may be a positive feature in winter but acts certainly very negatively in the summer by increasing discomfort and creating health problems for city dwellers; furthermore, it raises the level of oxidant pollution and increases energy consumption to cool buildings. In scenarios of global warming, UHI will increasingly grow as a nuisance. In this context, it was decided UHI mitigation was a priority. Prevailing N and NW wind circulation (circa 70% of the cases in summer afternoons) is hindered by the densely built-up southern and central neighbourhoods. By way of a numerical model, summer wind speed reduction until the 1980s (an important decade in urban expansion in Lisbon) was simulated (Lopes, 2002 and 2003). Wind speed decrease due to surface roughness was particularly important in the densely built-up southern city-districts (where z0 is - close to 1m) and over the Monsanto hill (200m, westwards from the most densely built-up areas, Fig.1). Nowadays, construction continues in the northern neighbourhoods although there are still large open spaces left. Lisbon has become a rather polluted city, and some evidence of air quality impoverishment has been recently (2004) pointed out at a conference on Lisbon Air Quality. Legal thresholds are sometimes exceeded, as was the case in January 1993 when frequent anticyclonic calm conditions occurred (Andrade, 1996). It is also clear that to improve air quality, air circulation should not be hampered. Based in our dialogue with planners and on the experience from authors working in the same topics (Zrudlo, 1988; Scherer et al., 1999; Feherenbach et al., 2001; several works referring to Germany quoted by Matzarakis, 2005; Baumüller et al., 2005, among others), it became clear that planners need very clear guidelines with regard to areas whose limits are very precisely drawn on a detailed map. To make steps in order to answer these questions, two climate maps have been prepared and will be included (for the moment only as annexes) in the new master plan for Lisbon: 1 - The Climatope Map (fig. 16): “areas of characteristic combination of climatic factors and of similar relative significance for their surroundings(…) “ that can be considered as ‘atmospheric response units’ (establishing a relation with the hydrologic response units ( Scherer et al., 1999, p.4187 ) As a help to construct the climatope map, a detailed cartography of Lisbon’s “physical” features (Map of Lisbon’s urban morphology for climatic purposes, fig. 12) was previously carried out, using a GIS. Based on Landsat images the landuse/landcover classes of the city were defined. Several processing tools (image enhancement, false colour composite, etc.) and supervised classifications (especially maximum likelihood technique and accuracy assessment) were used for that propose. A ventilation map was otherwise prepared, based on a DTM (fig. 13, 14 and 15). The final climatope map was obtained by crossing land use/cover units and ventilation classes (fig. 11 and 16) 2 - The map of climatic guidelines for urban planning (fig. 18). The climatope map was an indispensable cartographic tool for the drawing of the present map. The descriptive caption consists of one table (Table III) where recommended measures to mitigate UHI, enhance ventilation and decrease air pollution are listed. Guidelines differ according to the position within the city, topography and built-up density. For instance, in the northern part of Lisbon, setting up large green areas may be advised to moderate UHI, while in the city core, one can only recommend planting some trees in the rare areas still left. In the northern part of the city, large ventilation paths can still be preserved, while in the city centre, the only possible measure is to not obstruct the valley beds even further. Guidelines for planning with regard to each group of climatopes are synthesised below. Area of low density of the North of Lisbon (A, fig.18 and Table III) - As the gradient wind is not yet excessively slowed down, everything must be done to maintain this situation: this will lead to positive consequences not only in the northern city districts but also in central and southern Lisbon, preventing overheating and excessively high pollution values. As this is obviously an area with high building pressure, mainly in the NW sector, the guidelines are to avoid very densely built-up areas (H/W should be inferior to 1), to promote ventilation paths along large highways or between city-districts and create large green areas next to each new urbanized quarter. The southern limit of this area is indicated on Fig.16 as an important aerodynamic boundary. To the South of this limit, there is a great wind speed reduction due to Z0 ~1, while to the North of the same line there is still little wind speed modification. Areas of medium and high density, South of the aerodynamic boundary (B and C) - already very densely built-up (more so in unit C). Unit C comprehends the old town centre and most of the city built until the 1950s. There is hardly any room to plant green areas, though roof gardens could be a possibility and deciduous trees could be planted on some streets. Types of construction materials used to renovate buildings should be of a light colour and weak thermal admittance (Oke et al., 1991; Doulos et al., 2004). There is a habit of covering terraces with a dark isolating (from rainwater) material, which contributes to summer overheating of buildings and surface UHI. In unit B, H/W should be kept to less than 1 where buildings are still under construction. Ventilation paths (D) - The limits of this unit depend on three main factors: topography (in southern Lisbon, unit D corresponds to the main N-S and NW-SE valley bottoms in fig.16), built-up density (low built-up density axes in N Lisbon) and orientation along a roughly N-S direction (the same as the prevailing winds). In order to maintain suitable ventilation in these units, no high buildings oriented E-W should be allowed. Trees planted along these axes should not form dense windbreaks. If these rules are followed, better ventilation will lead to positive effects on temperature and air quality. Tagus Bank (E) - A narrow strip of land along the River Tagus is affected by Tagus breezes (35% of summer early afternoons) that have a very positive effect on thermal comfort in the summer. In S and SW Lisbon there is already a relatively high construction density, but building height is on average less than 15m. However, new city-districts have been built in the last decade in Eastern Lisbon. As construction continues, planners should be aware that buildings whose main length runs parallel to the Tagus bank prevent inland circulation of fresh air. So the two main guidelines for this unit is to avoid construction of very high buildings and to maintain ventilation paths perpendicular or oblique to the riverside. Green areas (F) - The positive influence of urban green areas is well known (climatic, biologic, hydrologic, social, cultural, etc.). Green areas of small dimensions are useful to dwellers in a neighbourhood and if their inner structure is varied (with ponds, lawns, tall trees, shrubs) several types of microclimates will be generated. Living at a short distance on foot from a small garden is one of the factors that contribute to the quality of life of urban citizens. Beside the influence inside the green area, it is well known that a medium- or large-sized park will modify temperature, humidity, radiant temperature and wind in the surrounding neighbourhoods (Wilmers, 1988; Spronken-Smith and Oke, 1998; Upmanis et al., 1999). So it is advisable to maintain existing green areas (and not replace them with parking lots) and to create others wherever there is enough space left. The new green spaces should have a diversified inner structure. Dense windbreaks should be included windward from leisure areas. Some of the results on Lisbon urban green areas have been recently published (Andrade and Vieira, 2005). Suitable planning will also lead to a decrease in energy consumption. Prior to calculations for the economical influence of different urban structures, a study of microclimatic conditions within urban canyons must be carried out. The CLIMLIS and the CML Projects proved an excellent opportunity to move from theoretical considerations to applied research. We wanted to give clear and simple guidelines with regard to specific places, because Portuguese management plans (Alcoforado and Vieira, 2004) usually provide only general and not always correct considerations as to climate. Our objective is to contribute to further discussions on the choice of the best methodology for this kind of work. As referred above, we have tried during the CML Project to surmount some of the difficulties involved in applied climatology (Oke, 1984; 2005; Eliasson, 2000). One of them is the need to have a dialogue with planners and this has now begun between the Geography Department of the University of Lisbon and the “Department of Strategic Planning” of the Lisbon City Council. This dialogue grew easier as work progressed and parts of the maps have been jointly drawn. We had to learn to transmit our “climatologic message” in a simpler and more comprehensible form (without losing scientific accuracy) and the planners we worked with explained to the University team what their needs and expectations were in terms of strategic planning. Although the inclusion of climate guidelines is not yet compulsory in master plans (unlike noise and pollution, whose levels are regulated by law), we are making efforts to make clear and disseminate the idea that climatic guidelines should be systematically included in master plans of urban municipalities.