CCMA5: UHI mitigation strategies II : urban planning
An urban model for analysing thermal effects dependent on spatial parameters
Urban Science and Systems, Department of the Built Environment, Eindhoven University of Technology, The Netherlands
Global warming is changing the urban climate and influencing human society. A report from Royal Netherlands Meteorological Institute (KNMI, 2013), showed that the temperature will rise globally by 1,0 -2,3°C in 2050 and 1,3 – 3,7 °C in 2085. To strategically deal with this issue, our research project aims at city planning incorporating climate change. KNMI has developed four scenarios to investigate the relation between land use planning and urban climate (KNMI, 2014), which are based on global airflow and temperature changes. Analysis of variance for the four scenarios on the national level indicate significant effects by different categories of land-use types on neighbouring areas.
In our research, a model is developed that links thermal maps with a land-use maps on the urban level. For this study, Rotterdam is used as a case study because it is a delta city, and more than half of the habitants are vulnerable to climate change (City of Rotterdam, 2013). For the case study, we employ thermal data from Landsat and land use data from the municipality of Rotterdam for a representative part of the city. With this model we analyse which spatial parameters such as building density, green spaces, road material, etc. are dominant in determining the city temperature. Following the four KNMI scenarios are applied to study the effect of climate change. In the paper we will report on the main local effects and how undesired heating/cooling could be prevented in future city planning.
Isfahan's Urban Design Sustainability with Climate During Safavid Period.
1Tarbiat Modares University, Iran, Islamic Republic of; 2Tarbiat Modares University, Iran, Islamic Republic of
Iran has a hot, dry climate characterized by long, hot, dry summers and short, cool winters. The climate is influenced by Iran's location between the subtropical aridity of the Arabian Desert areas and the subtropical humidity of the eastern Mediterranean area. Therefore, sunlight and its effects were an important factor of Persian gardens structural design. Textures and shapes were chosen by architects to harness the light. Iran's dry hot climate makes shade important in gardens. Trees and trellises largely feature as biotic shade; pavilions and walls are also structurally prominent in blocking the sun. The climate also makes water important, both in the design and maintenance of the garden. This subject has been explained in the first section of this paper by focusing on Persian garden's types and specially its garden city.
In the continuation, the paper will explain the Isfahan Garden City designing process as Capital of Safavid Dynasty. The city has been designed and planning for enhancing citizens' health and well-being. Sustainability with the climate and specially water supply for new gardens are subjects that have been solved in Isfahan's urban design. This section has explained the methods by which Safavid's had used for attaining sustainable water, shade and urban spirit in hot and dry climate of Isfahan.
Finally, this paper classifies the principles of urban design and the city axis features to indicate the inventions and adaptation to climate. The result of the study shows that Isfahan's urban design principles has used in accordance with climate conditions during Safavid period which was created a state of longevity in the design of the city and its environment.
Climatic aspects in the first city plan of Tel-Aviv (1925)
1Department of Geography and Human Environment and Porter School of Environmental Studies, Tel-Aviv University, Israel; 2Department of Geography and Human Environment, Tel-Aviv University, Israel; 3Albert-Ludwigs-University Freiburg, Germany
Our study examines the climatic aspects of the first city plan of Tel-Aviv (1925). This paper examines how the 1925 plan effected outdoor human thermal comfort in two periods: at the time of its implementation (1920-30s) and in the present (2010s). Additionally, the paper asks which of the two - shade or wind velocity – has greater influence on outdoor thermal comfort in the urban areas along the Israeli Mediterranean seashore.
The city of Tel-Aviv provides an ideal case study to examine these issues. Tel-Aviv was established in 1909 and grew rapidly. In 1925, the city had 34,000 inhabitants and there was a demand for a city plan. The task was given to Professor Patrick Geddes, who planned a city for 100,000 inhabitants that would spread along the Mediterranean seashore and would be suited to local environmental conditions. Geddes planned a grid of main streets, where the wide commercial streets stretched from north to south parallel to the sea. As a result, the main streets of Tel-Aviv were shaded most of the summer days but blocked from the sea wind. The plan was implemented during the late 1920s and 1930s.
To examine the thermal comfort at street level during the 1920's and 30's, a series of summer and winter climatological measurements were taken in the years 2010-13 and compared to historical climatic data from the 1920-30s. The historical city structure was then reconstructed virtually and the climatological measurements for 2010-13 were fed into the RayMan model to produce thermal comfort data (PET). The results show that in both summer and winter, solar radiation has a greater effect on thermal comfort than wind velocity. Consequently, the 1925 urban plan created improved thermal sensation in the main streets of Tel Aviv, mainly by the reduction of solar radiation.
Urban heat islands in the future Hanoi City: Impacts on indoor thermal comfort and cooling load in residential buildings
1Graduate School for International Development and Cooperation, Hiroshima University, Japan; 2Graduate School of Science and Engineering, Saitama University, Japan; 3Vietnam Institute of Urban and Rural Planning, Ministry of Construction, Vietnam
In Hanoi, Vietnam, a long-term urban development plan, namely Hanoi Master Plan 2030, was implemented in 2011. In the master plan, the population is projected to increase from 6.7 million in 2010 to 9-9.2 million by 2030. It is expected that the dramatic expansion of the city brought by the master plan would induce significant impacts on its urban climate, thus lead to the increase in cooling load in buildings during the summer months. In order to minimize the negative impacts, the master plan proposed a large and centralized urban green network comprising green belts and green buffers. However, the urban heat island (UHI) mitigation effects of the above green network have not been assessed scientifically in the master plan.
This study is composed of two sub-topics. Firstly, this study investigates the UHI effects in Hanoi under the present land use conditions as well as under those conditions proposed by the master plan through numerical simulations, specifically meso-scale urban climate modelling using Weather Research and Forecasting (WRF). Further, an UHI mitigation strategy with improved urban green network is proposed and the resulting UHI effects are also assessed. Secondly, the indoor thermal comfort and cooling load of a typical urban house is assessed in different climatic zones under the weather conditions of each scenario (i.e., current condition, master plan situation and mitigation scenario), respectively. The climatic zoning is derived from the cluster analysis based on the simulation results of the master plan condition.
The results of urban climate simulation show that even after implementing the master plan, the peak air temperature in the urban areas remains at the same level of 41°C. However, at night, the expansion of built-up areas largely increases UHI intensity and raises air temperatures in the planned built-up areas by up to 2-3°C. The centralized green spaces currently proposed in the master plan was thus insufficient to minimize the UHI impacts. In contrast, the newly proposed green network which equally distributes the urban forest in the city was more effective in the reduction of UHI intensity in the city (up to 1°C). Moreover, the new green network could reduce the amount of areas that experience the peak nocturnal air temperature by 56.5%.
The building simulation was conducted for the typical urban house using TRNSYS. The typical urban house was determined through the classification of building drawings based on the total floor area and room arrangements. Further, the computational model was validated with the results of field measurement conducted in a typical urban house of Hanoi in the summer month of August to September 2014. Empirical validation of the simulation model showed the satisfactory results in term of air and operative temperature (RMSE=0.33°C, R2=0.89). The further simulations are then carried out by using the spatial average of weather data from each climatic zone in three scenarios, respectively. Based on the above analysis, the impact of UHI effects on the indoor thermal comfort and cooling load in the typical urban house would be discussed. The indoor thermal comfort is evaluated under the assumption that the occupants will adopt natural ventilation when the indoor operative temperature is lower than the upper limit of adaptive thermal comfort criteria. The cooling load is then estimated when the indoor operative temperature exceeds the adaptive comfort level.
It was found that the average cooling load of typical row houses in urban areas is higher than that in rural areas. The increase of ambient air temperature due to the implementation of the master plan would likely cause an increase in the cooling demand, especially in the newly developed urban areas. This would force the occupants to use air conditioning more, thus result in a considerable increase in energy consumption for cooling in the future. Meanwhile, the newly proposed green network would more effectively moderate the increase in cooling load in residential buildings due to future urban development.
Thermal impact of blue infrastructure: Casestudy Cheonggyecheon, Seoul (Korea)
1University of South Australia, Australia; 2Bauhaus University Weimar, Germany; 3University of New South Wales, Australia
Seoul, the capital of the Republic of Korea, is influenced like many other large cities by the urban heat phenomena. The urban heat phenomena are typical for a metropolitan area that is significantly warmer than its surrounding rural areas due to human activities.
Special geographical and political conditions are combined with a high population density, remarkable high-rise buildings and small open spaces are characteristic for Seoul. The city of Seoul (9.8 Million inhabitants) is located in a valley surrounded by mountains in the north and south. Furthermore, in 1972 a restricted development zone (RDZ) precinct was established by the government. This is essentially a Greenbelt that has a size of 1,567 km². This greenbelt is more than two times larger than the city of Seoul. Seoul has an area of 605 km². All urban development within the RDZ has been prohibited during the last four decades.
After the full urbanization of the Seoul during the late 1980s several new towns where established outside the Greenbelt. Several push-and-pull factors have followed and influenced the rapid urbanization of the capital region of Korea. Currently more than 23 Million inhabitants are living in the Seoul Metropolitan Area (SMA). This has become one of the biggest urban agglomerations in the world.
The greenbelt has had a significant impact on the whole of the SMA. Due to the containment by the greenbelt, an intensive urbanization has occurred within the constrained Seoul City. This has resulted in a limited number of green areas and water bodies in the Seoul. The number of green spaces per inhabitant is one of the lowest in the world. Next to the 600m wide Han-River that flows from east to west through the central part of the city, there are no open streams or water bodies.
Therefore, the establishment of new green or water bodies in the Seoul City is of great importance. One of the most remarkable projects is the redevelopment of a 5.84 km long and 24 m wide two-tier expressway to a river stream.
We will investigate the micro-climate changes and urban-scale cooling load reduction which has resulted from the so called Cheonggyecheon water stream. This stream is located in central Seoul and runs from the northern central business district into the Han-River. After the Korean war (1950-1953) the Cheonggyecheon river was for more than 50 years covered with pavement and concrete overpass structures. The reconstruction of the expressway was carried out from 2002 to 2005. To estimate the thermal impact of the expressway into a water pathway remote sensing analysis (Landsat 7 ETM+) was undertaken. 20 Landsat-7 ETM+ images from 2000 till 2014 were used to compare the land surface temperature (LST) distribution during the time the expressway was there and through to the reconstruction and the establishment of the river stream. A built-up area of two km width surrounds the new water pathway and this was used as a reference area. The investigation could show that the establishment of the Cheonggyecheon stream forced a considerable thermal impact, i. e. an average decrease in the land surface temperature by seven degrees Celsius.
The results indicate that the cooling benefits of the restored stream areas are promising in the locations.
Simulating the extent of the moderating influence of green space distribution on future urban climates
Klimaat Consulting & Innovation Inc.
How a city thermally responds to weather directly impacts the health of its citizens. A changing climate, with higher temperatures and more frequent extreme events, together with growing and aging urban populations, motivates the need for better urban design. Thus, an understanding of the role of open space and vegetation to mitigate heat related health risks is valuable to urban designers and policy makers. However, these professionals may often be challenged to introduce extensive urban green space in urban (re)design projects as it competes against conventional and tangible urban real estate development benefits. Therefore quantifying how specific green space layout and distribution characteristics may positively influence local and city wide climate is helpful to show benefits that are just as tangible. In this work, an urban climate simulation process and its results are described and illustrated by means of a case study in China that identifies the spatial influence of different green space scenarios. The simulation process described herein allows multiple city and green space forms to be evaluated for different climate zones to develop climate responsive design rules for green space area ratios, distribution and layout. In particular, the process allows the scoring of green space integration in city design by evaluating the relative temperature modification or offset provided by its introduction.
A meteorology coupled urban climate simulation process is first described. The simulation process uses Open Source Computational Fluid Dynamic tools to simulate city wide wind exposure for a proposed large scale city (re)development. These wind simulation datasets are coupled with typical annual hourly meteorology data and a separate detailed solar exposure model and surface energy balance solver to predict the hourly climatic response for a given weather period. The computational solver and surface energy balance model also includes vegetation as porous moisture sources, so that the appropriate latent heat sink due to evapotranspiration, and solar shading effects can be modelled. Ultimately the process takes city geometry, vegetation plans and hourly meteorology data as input and delivers hourly surface and near surface temperature maps. Using the simulation process, a city redevelopment case study is evaluated under varying green space distributions for a number of different climates in China. Correlations between green space mitigation scenarios and the urban thermal response are presented and summarized in the findings.