Urban Ecology
mahsa samadpour shahrak; Mehrdad Karimimoshaver
Abstract
Highlights- The research considered the effect of planting patterns on thermal comfort.- The research addressed population increase and its effect on the morphology of cities.- The results of comparison between the scenario without trees and the others demonstrate that the thermal comfort conditions ...
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Highlights- The research considered the effect of planting patterns on thermal comfort.- The research addressed population increase and its effect on the morphology of cities.- The results of comparison between the scenario without trees and the others demonstrate that the thermal comfort conditions exhibit great changes, and all the scenarios create better environmental conditions than the scenario without trees.- The findings show that simply moving vegetation and trees without changing their nature and dimensions and the environment can improve comfort to some extent. IntroductionThe increasing population has changed the morphology of cities and caused changes in the surrounding environmental conditions. Green space per capita is about 4.5 square meters in Iran, which is quite different from the global standard: 20 to 25 square meters per person (Haashemi et al., 2016). As a result, it seems necessary to increase the amount of greenery in cities. Lee et al. (2016) introduce shading and ventilation as the main factors in the improvement of thermal comfort conditions in the environment using trees. Vegetation reduces mean radiant temperature and improves environmental conditions through evaporation and daylight control and reflection (Salata et al., 2017). It plays a major role in the regulation of weather conditions by controlling and conducting wind flow and reducing wind speed and pressure (Perini et al., 2018).Theoretical FrameworkThermal comfort involves conditions of perception in which the surrounding environment is thermally satisfactory (Ashrae, 1997). In their review of the studies conducted in the field of thermal comfort in outdoor spaces, Johnson et al. have introduced the predicted survey average index as one of the most widely used indices among ones such as SET and UTCI. (Johansson et al., 2013). This index has been widely used in different regions with different climates (El-Bardisy et al., 2016; Salata et al., 2015; Abdi et al., 2020).This model was designed by Fanger in 1970, considering factors such as air temperature, average radiant temperature, and relative humidity and two personal variables including clothing resistance and activity level, used as a composite index. This index specifies the coefficients that are measured according to Asher’s thermal scale and indicates the average thermal sensation of a large group of people in a certain space (Fanger, 1970). Therefore, considering and measuring this index causes other microclimatic factors to be taken into account and obtained through the following formulae:PMV=(0.303e-0.036m+0.028)[(M-W)-H-Ec-crec-Erec]E=3.05×10-3(256tsk-3373-pa)+EswEc=3.05×10-3[6.99×5733(M-W)-pa]+0.42(M-W-58.15)Crec=0.0014M(34-Ta)Erec=1.72×10-5M(5867-Pa).The value of H can be measured directly and calculated using the following equation:H=Kcl=tsk-tcl/Icl.Moreover, previous research has pointed out the importance of planting patterns, trees, and vegetation and their impact on the environmental and microclimatic conditions of the region. The question that arises now is what kind of tree planting pattern, among the common ones, can have a better impact on the environment. In this study, therefore, the four common planting patterns of sextuple, quadruple, row, and scattered were selected to be applied in the same conditions and with the same number of trees.MethodologyIn this research, the ENVI-met software was used because the output provides most of the parameters required for thermal comfort, such as Ta, Tmrt, and wind speed (Taleghani et al., 2015), and the results have been validated and used by researchers (Taleghani et al., 2018). For data measurement, five receptors were selected at the central points of the site. These receptors were located so as to be scattered in the site and be capable of expressing the general state thereof. Therefore, three receptors at the central points of the site and two located around the site were selected. Moreover, because the average human height between the positions of sitting and standing is 1.50 meters, the simulation measurement was carried out at this height. The environmental data and information on the receptors were extracted during the study hours (10 am to 9 pm), and the average value was calculated for the predicted survey average index.Results and DiscussionThe analysis of the data and figures extracted from the software demonstrates that a more uniform shade is created in the environment in the scattered pattern than in the others, and because the trees are scattered in most parts of the site, solar access is more limited there than in the other scenarios. Moreover, ventilation conditions are easier in the row pattern than in the scattered pattern, and the warm wind passes through the trees more easily there due to the regular arrangement. Therefore, the best planting pattern is the one that creates the more uniform shade and better ventilation conditions. However, the results of the scattered pattern are the same in most parts of the site, and there is only a little difference between them in some cases. As a result, the scattered and row patterns of tree planting are better than mass planting and concentrated in certain parts of the site.ConclusionThe results of comparing the treeless scenario to the others demonstrate that the thermal comfort conditions change to a large extent, and all scenarios create better environmental conditions than the treeless state. Moreover, because the row pattern exhibits a lower average PMV for most receptors and most hours of the day, it is the best pattern. The sextuple pattern has high indices in most cases, and the quadruple pattern has a similar function to the sextuple one. Therefore, it can be concluded that the row and scattered patterns create better comfort conditions than the others. The results of this research can be used by architects, landscape designers, and urban designers. In this research, different patterns of trees have been compared, so future research can involve comparison of other plantings such as grass and shrubs and of the effects of different planting patterns.
Urban Sustainability
seyed majid mofidi shemirani; seyedeh maryam hoseini; haniyeh sanayeiyan; gholamreza japalaghi
Abstract
Throughout the past century, cities have lost their vital connection with the nature due to the fundamental changes in their functions and physical forms. The development of urbanization and attachment of villages to metropolises in recent years have led to destruction of vegetation in these regions. ...
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Throughout the past century, cities have lost their vital connection with the nature due to the fundamental changes in their functions and physical forms. The development of urbanization and attachment of villages to metropolises in recent years have led to destruction of vegetation in these regions. The importance of identifying the effects of cities on their climates can be indicated only through accurate research and quantitative assessment. The overall increase in air temperature as a result of urbanization is 1-3 degrees Celsius. In stable climatic conditions, however, the air temperature difference between urban and suburban areas can be as high as 10 degrees Celsius. Increasing the amount of vegetation, planting trees, and developing ecological networks are some of the effective passive methods available for improvement of microclimates. Similar methods have been used in the ancient cities of Iran, where the temperature inside the cities has always been lower than that of the surrounding areas due to the utilization of a special type of urban planning which has been capable of providing appropriate climatic conditions at micro scale by controlling climatic elements. Ozgol is one of the northern neighborhoods of Tehran, where green spaces have diminished as a result of the development process and space quality at the centralized focal points has decreased. This study attempted to identify the relationship between green areas and temperature decrease on the hottest day of the year to help improve the quality of the public spaces and increase thermal comfort at the focal points of the neighborhood. This research used a hybrid methodology based on logical reasoning and software-assisted assessment to study a site in the Ozgol neighborhood under two conditions: current status and optimal design. The data on the current situation of the neighborhood were obtained by field measurements, and those on the latter situation were obtained via computer simulation and addition of plants to the area. Then, the PMV model was used for assessment of the comfort conditions and specification of the exact effect of plants on microclimate elements. The two conditions were compared, and the impact of urban design with plants on environment quality was evaluated. The evaluation criteria included temperature and relative humidity. The measurements were made at a height of 1.65 meters to prioritize pedestrian comfort. The findings suggested that allocation of a low percentage of city space to greenery can greatly improve microclimatic conditions. The computations indicated that every square meter of green space added to the area under study would expand the comfort zone by 3.71 times. The results also demonstrated that retention of the amount of relative humidity can reduce air temperature by 1.5-2 degrees Celsius. The findings of this study highlighted the significance of preserving the current green spaces over the neighborhood and the necessity of avoiding any change in the land use of the remaining gardens (about 6,000 m2 in the 4-hectare area of the site). The computations also showed that addition of the existing green spaces over the area by 2.69% can expand the area within the range of thermal comfort to twice as wide as the pre-intervention area. One the other hand, the issue of global warming, the 1-degree rise in the world’s temperature during the past century, highlights the value and significance of this 1.5-degree temperature decrease. Thus, it is possible to make significant changes through extension of the results of this study to a larger scale to involve the entire city.
