Kamusal açık alanlarda değişen mikro iklim koşulları ve dış mekân termal konfor: Taksim Meydanı ve Gezi Parkı örnekleri
Changing microclimatic conditions and outdoor thermal comfort in public open spaces: Examples of Taksim Square and gezi park
Yazar: EDA HAFIZOĞLU
Danışman: DOÇ. DR. GÜLDEN DEMET ORUÇ ERTEKİN
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Kentsel Tasarım Ana Bilim Dalı / Kentsel Tasarım Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Meteoroloji = Meteorology ; Peyzaj Mimarlığı = Landscape Architecture ; Şehircilik ve Bölge Planlama = Urban and Regional Planning

Özet:
Günlük yaya trafiğini ve çeşitli açık hava aktivitelerini barındırarak toplumun ortak kesişim alanı olan, kentsel yaşamı destekleyen ve kente nefes aldıran kamusal açık alanlar, sürdürülebilir kentsel çevre yaratmak için önemli tasarım unsurlarıdır. Doğal ve yapılı çevre bileşenlerinden oluşan bu kentsel açık alanlar, içerdikleri bitki örtüsü, su kütlesi ve döşeme malzemesi gibi çeşitli peyzaj elemanlarının oluşturduğu mekânsal farklılıklarla iklim bileşenlerini yerel ölçekte etkileyerek birbirinden farklı mikro iklim koşulları meydana getirmektedir. Bu koşullar bireylerin kendilerini termal olarak rahat veya stresli hissetmelerine neden olup mekân içerisindeki konfor durumlarını ve dolayısıyla mekân kullanımını ve beraberinde kentsel canlılığı önemli ölçüde etkilemektedir. Bu nedenle, kullanıcı sağlığı ile konforunu destekleyen kamusal açık alanların planlanması ve tasarlanması ve böylelikle, mikro iklime duyarlı günümüz ve geleceğin kentlerinin inşa edilmesi için yayaların açık alanlarda maruz kaldığı termal koşullardan duydukları memnuniyet düzeylerinin belirlenmesine ihtiyaç duyulmaktadır.  Bu kapsamda, dış ortamlardaki kullanıcı termal algılarının ve konfor koşullarının nesnel saha ölçümleri ve öznel değerlendirmeler üzerinden incelenmesi gerekmektedir. Bu iki yöntemin bir arada kullanılması, objektif verilerin yanı sıra kullanıcıların subjektif deneyimlerinin de dikkate alınarak daha kapsamlı bir şekilde değerlendirmelerin yapılmasına imkân sağlamaktadır. Küresel çapta yaşanan hızlı kentleşme süreçlerinin ve beraberinde artan nüfus yoğunluğu, betonlaşma, ekolojik bozulmalar ve iklim değişikliği etkilerinin esasen şehirlerdeki açık alanlar üzerinde baskı oluşturması nedeniyle özellikle son 20 yıldır dünya genelinde konuya ilişkin artan bir ilgi olmasına karşın, çalışmaların çoğu halen özgün veri eksikliğine sahip olup özellikle Türkiye'de yürütülen çalışmalar oldukça sınırlı sayıdadır.
Bu çalışma, objektif ve subjektif veriler üzerinden, İstanbul metropolünün merkezinde yer alan kamusal açık alanların yaz mevsimi gündüz saatlerindeki mikro iklim ve dış mekân termal konfor koşullarını analiz etmeyi, bu alanları ziyaret edenlerin termal algıları ile memnuniyet düzeylerini belirlemeyi ve yaz dönemi için bölgeye özgü termal konfor ölçeğini tanımlamayı amaçlamaktadır. Bu kapsamda, İstanbul'un Beyoğlu ilçesinde bulunan ve gün içerisinde şehrin en yoğun kullanım oranlarına sahip kamusal açık alanlarından olan Taksim Meydanı ve Gezi Parkı'nın mekânsal kompozisyonları ve bu mekânların gün içerisindeki doluluk seviyeleri göz önüne alınarak seçilen 4 lokasyonda, 30 Temmuz - 2 Ağustos 2022 tarihleri arasında, saat 10:00'dan 18:00'a kadar eş zamanlı olarak mikro iklimsel izleme ve rastgele seçilen yayalarla 400'ün üzerinde yüz yüze anket görüşmesi gerçekleştirilmiştir. Mikro iklimsel izleme kapsamında, görüşülen her bir birey için termal ortamların hava sıcaklığı, bağıl nem, rüzgâr hızı ve yönü parametreleri taşınabilir meteorolojik istasyon cihazları aracılığıyla ölçülmüştür. Anket görüşmeleri kapsamında ise, katılımcılardan cinsiyet, boy/kilo, yaş, etnik köken, son 1 saatteki aktivite düzeyleri, alanı ziyaret etme ve bulundukları konumları seçme nedenleri gibi kişisel bilgiler toplanmış ve anlık termal duyumlarını, termal koşulları kabul etme düzeylerini, termal tercihleri ile tercih ettikleri her bir iklimsel parametrenin seviyelerini ve genel konfor durumlarını ASHRAE ile McIntyre ölçeklerine göre oylamaları istenmiştir. Aynı zamanda, katılımcılar bulundukları lokasyonlar için tercih ettikleri peyzaj elemanlarını işaretlerken; bu esnada, katılımcıların giydikleri kıyafetler ve lokasyonlar içerisindeki konumları not edilmiştir. Sonrasında, seçili lokasyonların ve yakın çevrelerinin doğal ve yapılı çevre özellikleri fiziksel saha ölçümleriyle belirlenip ENVI-met mikro iklim simülasyon programında 3 boyutlu olarak modellenmiştir. Ardından, mikro iklimsel izleme kapsamında ölçülemeyen ortalama radyan sıcaklık parametresi oluşturulan 3B modeller ve ölçülen iklimsel parametreler kullanılarak ENVI-met programında her bir katılımcı için simüle edilmiştir. Dış mekân termal konfor hesaplamalarının yapılabilmesi amacıyla dış ortam koşullarını iyi bir şekilde temsil eden, çalışmalarda yaygın olarak kullanılan ve °C cinsinden ifade edildiği için anlama ve diğer parametrelerle karşılaştırma kolaylığı sağlayan Fizyolojik Eşdeğer Sıcaklık (PET) indeksi bu çalışma için seçilmiş olup katılımcıların PET değerleri, yapılandırılmış ENVI-met simülasyonlarına anket ve gözlemlerden elde edilen kişisel bilgilerin girilmesiyle hesaplanmıştır. Bunun sonucunda, ölçülen iklimsel parametreler ve hesaplanan PET değerleri ile anketlerden toplanan kişisel bilgiler ve oylar zamansal ve mekânsal olarak analiz edilirken; PET değerleri, bu değerlere karşılık gelen termal duyum oylarıyla basit lineer regresyona tabi tutulmuştur. Böylelikle, regresyon eğrisi üzerinden çalışma alanı için yaz dönemi nötr konfor sıcaklığı, termal konfor aralığı ve termal olarak kabul edilebilir konfor aralığı belirlenmiştir.
Çalışmanın bulguları, kamusal açık alanların içerdikleri çeşitli peyzaj kompozisyonlarına göre birbirinden farklı mikro iklim koşullarına sahip olduğunu ve dış ortamlardaki termal konfor seviyelerinin bu koşullara ve yayaların kişisel özelliklerine göre zamansal ve mekânsal olarak önemli ölçüde farklılaştığını göstermektedir. Aynı zamanda çalışma, termal koşulların algılanmasının ve değerlendirilmesinin yayaların deneyimlerine göre öznel bir sürece tabi olduğunu gösterirken; yayaların mekâna geliş amaçları doğrultusunda genel konfor durumlarını çoğu zaman termal hassasiyetleri üzerinden ifade etmeyebildiklerini, ancak farklı termal duyumlara ve tercihlere sahip olsalar bile kabul etme düzeylerine göre koşullara tolerans gösterebildiklerini kanıtlamaktadır. Ayrıca çalışma, dış mekân termal konfor aralıklarının yere özgü belirlenmesinin önemini vurgularken; aynı zamanda İstanbul için objektif ve subjektif verilerin eş zamanlı elde edildiği ilk çalışma olma özelliğini göstermektedir. Bu doğrultuda, açık alanların termal konfor koşullarının İstanbul gibi kentsel ısı adası sorunu yaşayan şehirlerde mikro ölçekte sorgulanması yere özgü sürdürülebilir kentsel politikaların oluşturulmasını sağlayarak günümüz ve geleceğin en şiddetli küresel ve ulusal sorunlarından biri olan iklim değişikliği ve sıcak hava dalgalarına karşı daha dirençli kentlerin yaratılmasına olanak tanıyacaktır.

Abstract:
Public open spaces, which are the common intersection area of society by accommodating daily pedestrian traffic and various outdoor activities, supporting urban life and breathing into the city, with their physical, ecological, economic, political and socio-cultural values, are important design elements to create a sustainable urban environment. These urban open spaces, which serve various purposes such as parks, sports fields, squares, plazas and streets, consist of natural and built environmental components and play an important role on the urban climate. Public open spaces, which show spatial differences depending on the various compositions of landscape elements such as vegetation, water body and paving material, create different microclimatic conditions by affecting the climatic components consisting of air temperature, relative humidity, amount of solar radiation, wind speed and direction on a local scale. At the same time, microclimatic conditions, affected by a number of environmental factors such as height-width ratio of buildings and associated streets, the orientation of the streets, the configurations of the buildings, the roof and facade materials, create different thermal environments where the individuals experiencing these spaces feel comfort or stress. Although the thermal sensation and evaluation of environments vary from person to person, this significantly affects the use of space and therefore urban vitality. In this regard, importance should be given to human thermal comfort in outdoor environments to plan and design public open spaces that support user health and comfort, thus building cities of today and the future sensitive to microclimate.
Thermal comfort expresses the level of satisfaction a person feels with the thermal conditions of the environment, which is addressed within three approaches developing over each other. The approach based on the heat balance of the human body is widely used in today's thermal comfort calculations because it is based on a scaled rational model. In this context, there are six main parameters to determine thermal comfort, including climatic and personal, and the combined effect of them expresses the ambient temperature perceived by individuals. These consist of air temperature (Ta), relative humidity (RH), mean radiant temperature (Tmrt) and wind speed (WS) which constitute the atmospheric conditions of the environment, and metabolic rate (M) and clothing insulation (Icl) levels of individuals who have exposed to these conditions. However, according to the psychological approach, since thermal comfort is a cognitive process, it is also affected by people's psychological states and consequently requires subjective evaluation.
Thermal comfort studies, which have been a subject of scientific research since the early 20th century, initially focused on indoor climatic conditions and the comfort sensations of building occupants, and in the following years, they began to be addressed in open spaces within the scope of the developing sustainable urban planning and design concept. Studies on outdoor thermal comfort have gained momentum, especially in the last 20 years, as rapid urbanization processes on a global scale and the accompanying increasing population density, concretion, ecological degradation, and climate change effects become more evident in cities, and essentially put pressure on open spaces. In this regard, many studies have been carried out on the heat stress of cities located in different geographical and climatic regions, and on the thermal sensations and comfort conditions of those who visit open areas such as city parks and city squares in these cities. However, it appears that there is a lack of original data in most of these studies and that thermal sensation categories and comfort ranges developed for Western and Central European cities are generally used as a reference. When the studies conducted in Turkey are examined, it is noted that the studies similarly lack site-specific data, and the number of them is quite limited. However, since the climate zone in which each city is located, and the climatic, environmental, and socio-cultural components of each region within the city differ, it is highly essential to use original data including both objective and subjective data in outdoor thermal comfort studies.
This study aims to analyze the microclimatic and outdoor thermal comfort conditions of public open spaces in the city center of Istanbul during the summer daytime, to determine the thermal sensation and satisfaction levels of pedestrians experiencing these conditions, and to define an original outdoor thermal comfort range for the summer period by using the objective and subjective data.
To the study's aims, in the first stage, Taksim Square and Gezi Park, which are located in the Beyoğlu district of Istanbul and are among the public open spaces with the highest usage rates during the day, were determined as the study area. These areas were considered together due to the absence of a sharp physical border between them and the existence of different micro spaces with landscape diversity and long-term outdoor activities such as resting, wandering, and doing sports in these spaces. Considering the periodic use of this city square and park and the increasing urban heat island problem of Istanbul, it was decided that field studies should be carried out during daylight hours in the summer period. 
In the second stage, for field studies, a total of 4 locations were selected by taking into consideration the landscape compositions of the micro spaces and the occupancy rates of these spaces during the day. The park includes; Location 1, which consists mainly of tall tree clusters with wide crowns, large grass surfaces and a water feature, and Location 2, which consists mainly of linear tree rows and grass surfaces with limited areas. The square includes; Location 3, which consists mainly of hard surfaces, and Location 4, which consists mainly of individual tree groups and hard surfaces. The Physiological Equivalent Temperature (PET) index – which best represents the outdoor conditions, is widely used in comfort studies and provides ease of understanding and comparison with other parameters because it is expressed in °C – was chosen amongst other thermal indices to perform outdoor thermal comfort calculations. Subsequently, daily and hourly regional climatic data were obtained from the 9 closest meteorological stations surrounding the study area, starting from the oldest record date until today. By analyzing daily climatic data, the dates between 30 July and 2 August 2022, which represent typical summer weather conditions for the Taksim region, were determined as the date range for field studies. According to the hourly climatic data and heat stress intensity changing throughout the day, it was decided to carry out the field studies between 10:00 and 18:00 hours, and the time period of the study was divided into equal 2-hour intervals: before noon, at noon, in the afternoon and in the evening. Equal time intervals not only represented the changes in thermal conditions during the day but also enabled easier interpretation and comparison of the data.
In the third stage, microclimatic monitoring and more than 400 face-to-face survey interviews were carried out simultaneously for 4 selected locations within the scope of the field studies. In microclimatic monitoring, the air temperature, relative humidity, wind speed and direction of the thermal environments for each individual interviewed were measured from a single fixed point using Kestrel 4500 and Kestrel 5500 portable meteorological station devices, which were calibrated to each other. In survey interviews, participants were randomly selected based on their having been in Istanbul for at least 6 months and in their location within the study area for at least 15 minutes, taking into account their thermal adaptation period. First, personal information such as gender, height/weight, age, ethnicity, activity levels in the last hour, reasons for visiting Taksim and for choosing their current location, etc. were collected from the participants. In the second part of the survey, participants used the 9- and 4-point ASHRAE and 3-point McIntyre scales to evaluate their thermal sensations (-4 to +4), their level of acceptance of thermal conditions (-2, -1, +1, +2), their thermal preferences (-1 to +1), their preferred air temperature, air humidity, wind speed and solar radiation levels (-1 to +1) and their general comfort status (-1 to +1). At the same time, the participants marked the landscape elements they preferred to determine what the environmental conditions should be like so that they could feel more comfortable in their locations. Additionally, during the survey interviews, the clothes worn by the participants and their positions within the locations were noted.
Additionally, at this stage, the natural and built environmental characteristics of the selected locations and their immediate surroundings were determined with in-situ measurements to calculate the mean radiant temperature through the 3D ENVI-met microclimate simulation model, which cannot be measured in microclimatic monitoring. In this sense, the amount of sky seen from the position of the measuring device in each location was photographed using a fish-eye lens to calculate the Sky View Factor (SVF), which expresses the rate of exposure to direct solar radiation and significantly affects the heat stress of individuals in the summer months. Then, using LIDAR technology, the height, crown width, trunk diameter and geographical position of the trees in the study area were calculated. At the same time, the crown form and specific trunk, branch and leaf characteristics of the trees and the structural forms and positions of other vegetation such as shrubs and ground covers were obtained through field observations. In addition, vegetation species were identified using the PictureThis – Plant Identifier mobile application, based on close-up photographs of them. Finally, an inventory was constructed by adding other specific data such as the topography and subsoil layer characteristics of the site, street widths, building dimensions, materials, colors and dimensions of the roof, facade and pavement, electricity and lighting poles, subway entrances and exits, seating units, and water features, etc. thanks to the Google Earth Pro application, literature search and field observations.
In the fourth stage, the SVF values of the locations were calculated by integrating the fish-eye photographs taken into the SkyViewFactorCalculator 1.1 software. In addition, mathematical calculations were made based on personal information from the surveys and clothing levels from observations to determine the participants' metabolic rates and clothing insulation values. At first, basal metabolic rates for both genders using height and weight information; and secondly, muscle metabolic rates using the duration of activity levels in the last hour and the sum of their corresponding rate values were calculated separately. The values of metabolic rate obtained by summing these rates were subjected to the Dubois equation and brought into the appropriate format for thermal comfort calculations in the ENVI-met model. Similarly, thermal insulation values corresponding to each piece of clothing worn were determined, and additions were made as regards the instantaneous positions of the individuals within the location. Thereafter, 4 locations and their immediate surroundings were modeled in 3D through SketchUp Pro 2023 software in line with the inventory data, and then their natural and built components were detailed in ENVI-met Version 5.1.1 simulation software. Afterward, the mean radiant temperature value for each participant was simulated in the ENVI-met program according to the participants' positions, using the created 3D models and measured climatic parameters. Subsequently, individual PET index values were computed by entering the participants' physiological characteristics, pre-calculated metabolic rate and clothing insulation values, and their instantaneous positions, along with the days and hours of the surveys, into ENVI-met simulations.
In the final stage, minimum, average and maximum values of both measured climatic parameters and the calculated PET index, as well as personal information and votes collected from the surveys, were analyzed on the basis of survey locations and time intervals. Furthermore, simple linear regression analysis was performed between thermal sensation votes (TSV) and general comfort votes (OCV) to examine whether the data were dependent or not. Similarly, PET values were subjected to linear regressions separately with each of the 6 main parameters that have a direct impact on thermal comfort, as well as with TSV values. Finally, using the PET and TSV regression curve, summer neutral comfort temperature (TSV = 0), thermal comfort range (TSV = -0.5/+0.5) and acceptable thermal comfort range (TSV = -1/+1) in terms of PET were calculated for the study area.
The findings of the study show that the 4 locations selected from Taksim Square and Gezi Park have different microclimatic conditions depending on their various landscape compositions. In this context, the highest values of average air temperature and mean radiant temperature for summer daylight hours are at Location 3 (Ta = 29.75°C, Tmrt = 63.54°C), but the lowest values are seen at Location 1 (Ta = 27.19°C, Tmrt = 25.84°C). On the other hand, Location 1 (RH = 58.44%, WS = 2.27 m/s) has the highest values of average relative humidity and wind speed; the lowest value of average RH is observed at Location 3 (53.02%), the lowest value of average WS is observed at Location 2 (0.93 m/s). At the same time, the study proves that thermal comfort levels in outdoor environments vary significantly between locations in compliance with climatic and user-related parameters. In this respect, average PET values are obtained highest at Location 3 (43.25°C) and lowest at Location 1 (34.23°C). Additionally, it is noteworthy that the highest and lowest levels of PET values persist in the same locations throughout the day, although they vary temporarily for each location. Therefore, it can be said that the perceived ambient temperature is highest at Location 3, contrary to this, the comfort level felt from thermal conditions is highest at Location 1. In addition, when the correlation coefficients between the 6 main parameters and PET index are examined, it is seen that air temperature (R2 = 0.99) has the highest dependence, but wind speed (R2 = 0.71) has the lowest dependence on PET values.
On the other hand, the study confirms that users generally perceive the ambient temperature as cooler, as the cooling effect increases as the landscape diversity within the locations increases, and this perception is largely preferred by users, especially during the daytime in the summer months. In this context, the survey results show that the neutral votes (TSV = 0), which correspond to the thermal sensation level where participants define the ambient temperature as neither hot nor cold, are highest at Location 4 (15.5%), but lowest at Location 3 (6.5%). According to the vote distribution, Location 1 is rated as 'slightly cool and cool' with 48.7%; Locations 2 and 4 are perceived as 'warm and hot' with rates of 55.5% and 56.1% respectively. In this regard, the highest rate of participants who want the ambient temperature to remain constant is seen at Location 1 (82.6%). On the contrary, Location 3 is perceived as 'very hot' by 13% of the participants and has more than 85% positive thermal sensation votes, and hence stands out as the location where the cooler ambient temperature is most desired with a rate of 66.7%. Furthermore, the study proves that even if users have different thermal preferences, they can tolerate thermal conditions depending on their level of acceptance. Compared to Locations 1 and 2, Location 3 has the highest number of unacceptable and absolutely unacceptable votes with a rate of 30.6% and Location 4 has the highest number of absolutely unacceptable votes with a rate of 10.3%. Concordantly, it can be seen that the ambient temperatures for each location are generally found to be acceptable by the participants, despite the low neutral vote rates and the distribution of acceptable votes.
Moreover, the study indicates that users do not often express their general comfort status through their thermal sensitivity (R2 = 0.20) in line with their purpose of coming to the locations, and consequently, thermal comfort may have a partial effect on the perception of comfort in the space. When the regression curve of TSV and PET is examined, it is obvious that there is a high relationship (R2 = 0.76) between PET values obtained from objective measurements and TSV values obtained from subjective evaluations. Therefore, it can be said that as PET values increase or decrease, the thermal sensations are moved away from the neutral level. Besides, based on this regression curve, the neutral comfort temperature is 29.3°C PET, thermal comfort range is between 25.9 – 32.6°C PET, and the acceptable thermal comfort range is between 22.6 – 36.0°C PET in summer conditions for the region.
As a result, while this study emphasizes the importance of site-specific determination of outdoor thermal comfort scale, it is also the first study in which objective and subjective data are carried out simultaneously for Istanbul. In this regard, questioning the thermal comfort conditions of open spaces on a micro-scale will enable the creation of site-specific sustainable urban policies and of cities that are more resistant to climate change and heat waves, which are among the most severe problems of today and the future.