Evaluating Urban Heat Island Effects in Malang City Parks Using UAV and OBIA Technologies

The phenomenon of LST change is an important issue in urban environmental studies. High LST can affect people's quality of life, health and urban ecosystems. Through an in-depth understanding of the distribution of LST and the factors that influence it, it can help in planning a more sustainable city in the future, especially in the context of climate management efforts.

Urban areas are complex and dynamic ecosystems [1] that have a higher growth rate than the surrounding areas [2]. This growth is characterized by the high conversion of undeveloped land into built-up land, which if done without proper supervision and planning, can have detrimental effects including microclimate change [3]. Malang City has shown the effects of climate change, which is characterized by an increase in the average LST of more than 2℃ in the period 1997-2018 [4]. Given the conditions of population growth every year in Malang City which has an impact on increasing land conversion, it can be predicted that the average LST will also increase in the following years.

Urban parks are a major component of urban carrying capacity that can directly affect the microclimate [5]. Meanwhile, the quality of existing city parks in Malang City has not shown an optimal function as a whole, especially in the ecological aspect due to the lack of vegetation elements [6]. Among other things, this is indicated by the availability of vegetation components that are still not comprehensive, which is felt by visitors through the existence of areas with high temperatures during the day, especially in Merdeka Square Park in locations that have not been shaded by vegetation [7]. So that the analysis to determine the condition of the distribution of land cover material types and the distribution of LST in RTH is important to assess whether the study site is in the temperature category that can be tolerated by visitors, which can have an impact on the productivity and comfort of visitors in the park.

To determine the classification of land cover material and the distribution of LST, remote sensing technology is used. One of the tools from remote sensing that is starting to be widely applied for data collection is an UAV or drone. The use of UAVs in remote sensing is more effective for obtaining data that is more detailed, real time, fast, and cheaper. In addition, the images obtained are also cloud-free so that the images formed can be processed with better results [8]. However, it is still rare to apply the OBIA combination in land mapping using drones [9].

After obtaining the output of drone image processing in the form of RGB images, the image classification stage is then carried out into several classes based on the type of land cover material using the OBIA method. The OBIA approach has been shown to be more effective than pixel-based classification techniques in extracting features from ultra-high-resolution imagery through its ability to distinguish patterns among the complexity of urban landscapes. OBIA can classify images according to the shape, color, and feature characteristics of groups of pixels, resulting in image objects that are more in line with the physical landscape of the feature [10]. As for the LST distribution data obtained through data processing in the form of samples of thermal points captured by thermal cameras on drones using the kriging method. The kriging method is basically to process data samples in the form of points or points into distribution or raster data.

The objectives of this research include classifying the type of land cover material in several city parks in Malang City using the OBIA method along with the distribution of LST values through remote sensing methods by utilizing high-resolution UAV imagery and the OBIA method. Then further analysis was carried out to identify factors that influence LST variations. The results of this study are expected to provide useful information for urban spatial planning and environmental management in Malang City.

The hypothesis or basic assumption by researchers is that the average LST is higher in Merdeka Square Park. While Merbabu City Park has an average LST below Merdeka Square Park and Malabar City Forest has the lowest average LST. This is due to the intensity of the type of built land use and community activities that are more crowded and dense in Merdeka Square Park. Meanwhile, Merbabu Park and Malabar Forest will have an average LST value that tends to be lower because the type of land cover around them is residential with community movements that are not as busy as Merdeka Square Park.

3.1 Image classification with OBIA

Object classification using the OBIA method produces a map of the distribution of land cover material classifications in the city park area and its surroundings. Pada penelitian ini, metode OBIA digunakan dengan software eCognition Developer 64. The following are the segmentation stages of OBIA shown in Figure 2.

Based on Figure 2, the segmentation results can be seen in the form of grouping pixels that have similar color and texture characteristics into groups of segments. The level of detail of the formed segment can be set by the user according to their needs. The setting is in the 'multiresolution segmentation' tool by filling in the numbers freely, generally ranging from 30-200 but can be adjusted according to needs. For this study, a segment detail level of 50 to 100 was used to adjust to the differences in the scale of the three study locations. The determination of the use of the segment detail level is because, at that number, the segments produced have been able to group pixels with the same characteristics so that they are able to classify different objects in the image. After the segments are formed, the classification stage is carried out by creating training samples based on segments from each land cover class. The more training samples that are formed, the better and more accurate the classification results will be. To get the best classification results in this study, users create as many training samples as possible in almost all segments. This aims to reduce the occurrence of classification reading errors by the software system so that the classification results will be better. After completing the training sample, the software system then performs the classification process with the ‘classification’ tool. To increase the accuracy of the classification results, this software also offers editing options by users for segments that have misclassification. These results show that the use of the OBIA method is effective in classifying high-resolution images because errors in classification results can be minimized because users have control in selecting training samples and editing classification results that have been formed by the system.

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Figure 2. OBIA segmentation (a) Segment of Merdeka Square Park (b) Segment of Merbabu Park (c) Segment of Malabar Forest

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Figure 3. Classification of land cover materials (a) Classification of Merdeka Square Park (b) Classification of Merbabu Park (c) Classification of Malabar Forest Segment

After obtaining the classification results, a validation test was carried out on the level of land cover classification accuracy at the third location with the kappa coefficient. The sample points used were 90 points per research location which were distributed using stratified random sampling. The kappa accuracy values in this study were 0.93 for Taman Alun-Alun Merdeka, 0.93 for Taman Merbabu, and 0.91 for Hutan Malabar. The values of the three kappa coefficients are in the range of 0.81-0.99 so that they are categorized as having a very good chance of accuracy according to Landis and Koch (1977) in the study of Nishar et al. [15]. The following are the results of the system classification after sampling several segments based on the class of land cover material types in the three parks and city forests and several surrounding areas in Malang City, shown in Figure 3.

Based on Figure 3, it shows that there are variations in the land cover of the three study sites. Basically, land cover types are classified into built-up land, vegetation and water. However, in this study, a more detailed classification is carried out based on the type of material. The following is the area of each type of land cover from the three study locations in the form of areas within RTH and some of the surrounding areas. The area and percentage of land cover materials can be seen in Tables 1-3.

Based on the tables, it is known that the extent of material types in the three study locations varies. Inside the RTH area, it is dominated by vegetation, especially trees, as indicated by the large percentage of area compared to other types of land cover. Meanwhile, outside the RTH area is dominated by built materials such as roof tiles, concrete, and asbestos due to land use in the form of residential areas.

Table 1. Land cover materials area of Merdeka Square Park

Table 2. Land cover materials area of Merbabu Park

Based on the identification results of the condition of the distribution of land cover material types in the three green spaces using the OBIA method. It shows effective classification results. This is because the OBIA method can produce a classification of 10 to 11 classes with a high level of detail at the micro research scale. The segmentation stage in the OBIA method can classify each pixel based on color and texture into segments which are then classified in a supervised classification or control by the user so that the classification results formed can be adjusted to the wishes of the researcher to get the best results. Based on these results, the researcher considers that the OBIA method is effective in classifying objects that require a high level of detail.

Table 3. Land cover materials area of Malabar Forest

3.2 LST distribution

LST data in this study is sourced from high-resolution images as a result of processing of samples captured by thermal cameras on drones. The pixel accuracy of the LST data at the three study sites reached 10 to 100 cm. The pixel size indicates a much higher quality compared to satellite imagery. The following is the LST value classification of the locations shown in Figure 4.

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Figure 4. Classification of LST value (a) LST classification of Merdeka Square Park (b) LST classification of Merbabu Park (c) LST classification of Malabar Forest

Based on Figure 4, it is known that the pattern of LST distribution when viewed from high-resolution images shows diverse variation details. This shows that high-resolution imagery is relevant when conducting LST analysis studies on the complexity of urban elements, especially micro-scale research such as green spaces. In addition, it is also known that within the RTH area generally tends to have low LST values due to the dominance of land cover in the form of vegetation. Meanwhile, the area outside the RTH has a higher LST value. Based on calculations with tools on QGIS, the results show that the average LST in the Merdeka Square Park area is 38.79℃, Merbabu Park is 35.33℃, and Malabar Forest is 33.18℃. The percentage of each LST class in each study location can be seen in Tables 4-6.

Table 4. LST classification value of Merdeka Square Park

Table 5. LST classification value of Merbabu Park

Table 6. LST classification value of Malabar Forest

Based on the tables above which show the classification of LST distribution in Merbabu Park and Malabar Forest, there is a dominance of the very low LST category. It can be observed in Figure 4 that both locations are dominated by dark green and light green colors. Especially in the area inside the RTH. Unlike the case with Merdeka Square Park which is dominated by the high LST category. This is partly due to the absence of overall vegetation shading in the Merdeka Square Park area and the use of land cover materials that are solar radiation transmitting materials such as paving, land cover that is a solar radiation transmitting material such as paving.

3.3 Correlation between land cover materials and LST

In this study, the relationship between land cover area and LST distribution pattern in urban parks in Malang City was analyzed using OBIA method. Data were taken from three main parks: Merdeka Square Park, Merbabu Park, and Malabar Forest. Each park showed variations in the type and extent of land cover that influenced the LST distribution pattern. A detailed discussion of these relationships follows.

3.3.1 Merdeka Square Park

In Merdeka Square Park, trees dominate the land cover with 34.92% of the total area. These trees contribute significantly in lowering LST due to their ability to absorb and reflect solar radiation and provide effective shading. Low vegetation and grass, although only covering 0.81% and 5.26% of the total area, also help to lower the temperature through the process of evapotranspiration.

Hard materials such as asphalt (18.37%), paving (9.42%), and concrete (13.44%) absorb and re-emit heat radiation, increasing the LST in the area. The surface temperature distribution in this park shows significant variations, with areas dominated by vegetation showing lower LST, while areas with hard materials show higher LST. For example, the LSTs in the tree-dominated areas were in the very low to low temperature category, while the areas with asphalt and concrete showed high to very high temperatures. It can therefore be seen that the type of land cover material, which can generally be divided into vegetation and building material, has a direct influence on the LST value.

3.3.2 Merbabu Park

Merbabu Park has a dominance of trees reaching 33.77% of the total area, which contributes greatly in lowering LST. Low vegetation and grass cover 3.34% and 3.13%, respectively, helping to lower the temperature albeit on a smaller scale. Hard materials such as concrete (14.00%) and paving (6.61%) contribute to the increase in LST due to their high heat-absorbing capacity.

The distribution of LST in Merbabu Park shows that areas with many trees and vegetation tend to have lower temperatures. In contrast, areas with hard materials show higher temperatures. Very low LST is dominated by areas with trees and vegetation, while high LST is dominated by areas with concrete and paving.

3.3.3 Malabar Forest

Malabar Forest has the highest percentage of trees among the three parks, at 47.74%, which contributes significantly to lowering LST. Low vegetation and grass cover 1.56% and 2.01% of the total area, helping to keep temperatures low. The presence of hard materials such as concrete (7.10%) and paving (3.54%) is present in this park, but their effect on increasing LST is less significant compared to the dominance of vegetation.

The distribution of LST in Malabar Forest shows that areas with tree dominance have very low to low temperatures. Materials such as zinc/asbestos (13.27%) and roof tiles (13.83%) which have a high heat storage capacity show a higher LST, although their area is smaller compared to vegetation.

3.4 Increasing urban green spaces

Based on the results of this research study, it was found that variations in land cover, especially the variables of land cover material type, density of built-up land, and the presence of vegetation components are the main factors that can affect LST distribution patterns, especially in urban areas. Areas with high building density and not accompanied by the presence of sufficient vegetation tend to have higher LST values. Higher vegetation density and proximity to water bodies play an important role in moderating LST, leading to cooler summers and warmer winters [19]. Areas with low vegetation trigger an increase in LST, while areas with dense vegetation trigger a decrease in LST [20].

The main factor affecting the decrease or increase of LST as studied in this research is the types of materials that make up the land surface or ground cover. Different types of materials can have different effects on LST [21]. That is because the type of ground cover will affect the reflectivity of the sun that falls on the surface. The reflectivity of solar radiation can then cause an increase or decrease in temperature around the area [22].

Based on the results of this research study, it can be seen that the types of land cover materials that have the ability to reflect solar radiation or low albedo are vegetation components such as trees, grass, ornamental plants. It is as shown in the results of data processing that the value of LST distribution on vegetation components is in the very low to low LST category. While the types of land cover materials that have the ability to reflect solar radiation or large albedo are building material components such as paving, concrete, asphalt, roof tiles, and asbestos. This is characterized by a large distribution of LST values on these land cover components. Solar radiation that reaches the material will heat the pavement surface and then heat the air temperature above it [23].

3.5 Recommendations for sustainable city park design

The following is a further explanation of the types of land cover materials and their ability to reduce or increase LST values:

1) Planting Trees with Broad Canopies

Basically, the type of vegetation planted will also affect the surrounding LST conditions. The characteristics of vegetation with high crown density will be more effective in reducing the temperature under and around trees. Trees have the potential for long-term CO₂ storage compared to non-woody vegetation or other than trees. So in an effort to reduce the ambient temperature of an area can be done by planting trees with wide and dense crown characteristics to reduce the intensity of solar radiation entering the inside. Plants with higher canopy density have a larger surface area for evapotranspiration and provide more shade, resulting in a greater temperature reduction than trees with lower canopy density [24].

Selecting plants with thick canopies, dense leaves, and high canopy density values can contribute significantly to cooling, humidification, and shading, thereby increasing human comfort in understory vegetation with lower canopies [25]. Trees with wide and dense crowns can retain, reflect, absorb and filter solar radiation [26].

The vegetation planted in the three study sites has a variety of species. However, all three tend to be dominated by Banyan Trees, Mahogany Trees, Kiara Payung Trees, Ketapang Trees, and Trembesi Trees. These trees are characterized by trees that have wide crowns so that they can provide maximum shade and can effectively affect the quality of the surrounding microclimate [27]. The quality of vegetation components in the three study sites can be proven by the presence of significantly lower LST distribution in the land cover in the form of trees, which indicates that the trees in the three RTH areas have the ability to reduce temperature, increase humidity, and ward off solar radiation.

Conversely, vegetation characteristics that should be avoided to be planted especially in the RTH area are plants that do not have the ability to effectively absorb solar radiation so that they are unable to reduce the heat around them and can actually produce a lot of air pollutants or toxic gases. Among these types of vegetation are sea cypress trees, bamboo trees, several varieties of pine trees, and desert plants. Trees characterized by slender trunks, small leaves and habitats in hot and dry climates tend to be ineffective in reducing temperatures. Slender trunks bend more easily and are more susceptible to mechanical damage during strong winds, potentially limiting their ability to provide consistent shade and cooling effects [28, 29]. In addition, trees with small leaves may have higher transpiration rates during the day, leading to increased water loss and potentially reduced cooling effects in hot and dry conditions [30].

The location of additional vegetation in each park also needs to be considered, especially in areas that are not yet shaded by trees. Areas that have not been shaded by trees will have an impact on high LST values, especially in areas that are built material. In Merdeka Square Park, additional vegetation can be added, especially in the middle of the park because the area uses paving material and has not been shaded by trees, while the area is also one of the areas with a high level of visitor crowds because visitors can carry out various activities such as playing, sitting, feeding birds, and so on.

In Merbabu Park, additional vegetation can be done in the northern part of the park because the area uses built materials such as paving and concrete and has not been shaded by trees so that it provides a heat effect due to high LST values in the area, especially during the day. Meanwhile, Malabar Forest basically has sufficient quantity and quality of vegetation. The vegetation in Malabar Forest has shaded the entire urban forest area so that it can provide comfort for visitors to do activities in the urban forest as a whole.

2) Use of Eco-Friendly Materials

Buildings materials can essentially increase the temperature of the surrounding area due to their higher reflectivity of solar radiation, resulting in a heat effect on the surroundings. Materials commonly used in urban environments, such as concrete, asphalt, and stone, have been identified as contributors to the urban heat island effect due to their ability to absorb and retain solar energy, which then releases it as heat [31]. Materials with low heat reflection capacity and high heat absorption rates, such as asphalt pavement, can contribute to increased surface temperatures in urban areas during summer [32].

Therefore, in green space areas, it is better to reduce the use of building materials such as concrete and paving to environmentally friendly ground cover materials. Compared to using these material components, it is better to replace them with grass, grass blocks, and ornamental plants because grass is one of the ground cover plants that can absorb solar heat. Grass has the ability to break down carbon dioxide into oxygen. Although grass is a type of low plant, at least the surface temperature in areas covered by grass is lower than other materials [33]. In addition, there are also several methods that can be done to modify building materials to help reduce the urban heat island phenomenon and improve thermal comfort in urban areas based on the study of Pratiwi [34] as follows:

1. The use of permeable or perforated paving to help absorb less heat than solid paving. Permeable pavements, including interlocking permeable concrete pavements, pervious concrete, and porous asphalt, have been identified as effective solutions for flood mitigation and heat dissipation in urban areas [35]. These materials have high levels of long-wave radiation, allowing for better heat absorption and release, which can help reduce surface temperatures [36].
2. Use of reflective paints or coatings that can reduce heat absorption. Reflective coatings, such as low-emissivity paints and infrared reflective coatings, have been developed to control heat exchange between the interior and exterior of buildings, thereby reducing heat absorption [37, 38]. These coatings are designed to have high reflectivity properties, which help minimize the amount of solar radiation absorbed by the surface, thereby lowering the temperature in the surrounding area [39].
3. Proper use of aggregates and mixes that create an asphalt or concrete mix that is lower in heat absorption. Mix composition is also important in heat absorption. The use of lightweight aggregates in concrete can reduce its density and thus impact its heat absorption properties [40]. By partially replacing cement with ground blast furnace slag (GGBS) in concrete mixes, the heat resistance of concrete can be improved, thereby reducing high temperatures and increasing compressive strength [41].
4. Adjusting the placement pattern of paving materials or concrete to minimize open areas that can absorb heat directly from the sun such as placing under areas shaded by trees. One effective method is to incorporate shading elements such as trees to reduce exposure to direct sunlight, as research shows that shading can lower the heating of paving materials and protect the surface from direct sunlight, thus aiding in temperature reduction [42].

3) Building Water Based Elements

The water element basically has the ability to change from liquid to vapor so that the surrounding air temperature becomes cooler [43]. The process of changing the form of water from liquid to vapor and back to liquid through evaporation and condensation is a fundamental mechanism in the cooling process. When water evaporates, it transitions from liquid to vapor state, absorbing heat from the surrounding environment in the process, which contributes to the cooling effect [44]. The water element can affect the microclimate through the wind direction that carries splashes of water and water vapor as well as evapotransportation from the water or plants in the pond to the surrounding area.

Based on the study in this research, it is found that the water element in the city park, namely the fountain in Merdeka Square Park, has a much lower LST value and has a cooling effect on the surrounding area. This shows that the water element is effective in reducing the temperature in the surrounding area so that the addition of water elements in RTH is important in creating a more comfortable microclimate.

The strategy that can be done to improve the quality of microclimate through improving the water element in Merdeka Square Park is to reactivate the fountain facility in the center of the park. This is because every time researchers visit the park in the morning to evening there is never any fountain activity so that it is only a puddle. Water elements that have movements such as fountains or flows can provide a cool or cool effect more effectively on the surrounding area.

The strategy of adding water elements that can be done in Merbabu Park includes adding fountain or pond facilities in the northern part of the park. This is because the northern part of the park is only built empty land with paving material without any activities that can be done. By improving the area through the addition of water element facilities, it is hoped that it can improve the park's microclimate.

3.6 Public awareness and engagement

Engaging the public in understanding the benefits of sustainable urban design, particularly in urban parks, is essential for fostering community participation in green initiatives. The integration of technology, such as UAV and OBIA methods, enhances this engagement by providing valuable data that can inform and involve the community in sustainability efforts.

Urban parks are vital components of sustainable urban design, contributing to environmental quality, biodiversity, and community well-being. Research has shown that the use of UAVs in monitoring park attributes allows for comprehensive assessments of park usage and environmental conditions [45]. This technology enables the collection of high-resolution data that can be used to analyze LSTs, which is crucial for understanding the urban heat island effect and its implications for park design and management [46]. By employing UAVs, urban planners can visualize and communicate the benefits of green spaces more effectively, thereby raising public awareness and encouraging community involvement in park-related initiatives.

The application of OBIA methods in analyzing UAV imagery further enhances the ability to classify and map urban vegetation and other park features accurately. OBIA segments images into meaningful objects, allowing for more precise assessments of vegetation health and diversity [47]. This capability is particularly important in urban parks. Where diverse plant species contribute to ecological resilience and aesthetic value. By sharing these findings with the community, urban planners can foster a greater appreciation for the ecological benefits of urban parks, motivating residents to participate in conservation and enhancement efforts [48].

Moreover, community engagement in the assessment and management of urban parks can lead to more sustainable outcomes. Studies have indicated that when local communities are involved in the planning and monitoring processes, they are more likely to support and maintain green initiatives [49]. For instance, participatory approaches that incorporate community feedback into park design can ensure that the spaces meet the needs and preferences of local residents, thereby enhancing their usability and enjoyment. This collaborative effort not only empowers communities but also builds a sense of ownership and responsibility towards the urban environment.

Effective communication strategies are essential for promoting public understanding of the benefits of sustainable urban design. Utilizing visual data derived from UAV and OBIA methods can help convey complex environmental information in an accessible manner. For example, interactive maps and visualizations can illustrate the impacts of urban heat and the benefits of vegetation cover, making the case for increased investment in green spaces more compelling [50]. Additionally, educational programs that highlight the role of urban parks in climate adaptation and community health can further engage the public and encourage participation in sustainability initiatives [51].

One of the foundational aspects of promoting sustainable urban design is the alignment with the Sustainable Development Goals (SDGs), particularly SDG 11, which focuses on sustainable cities and communities. This alignment serves as a guiding framework for local sustainability goals, emphasizing the importance of community involvement in urban planning and development [52]. Research indicates that community engagement is beneficial for sustainability, as it fosters a sense of ownership among residents, encouraging them to contribute resources and actively participate in sustainability initiatives [52, 53]. This participatory approach is essential for ensuring that urban design reflects the needs and aspirations of the community, thereby enhancing the overall effectiveness of sustainability efforts [54].

Moreover, interdisciplinary collaboration plays a significant role in enhancing community engagement in sustainable urban design. For instance, integrating engineering education with social work principles can equip future engineers with the skills necessary to design projects that are not only technically sound but also socially responsible [55]. This interdisciplinary approach can lead to more innovative solutions that address the complex challenges of urban sustainability while fostering community involvement [56]. By involving various stakeholders, including local governments, non-profit organizations, and community members, urban design processes can become more inclusive and responsive to the diverse needs of the population [57].

Effective communication strategies are also crucial for raising public awareness about the benefits of sustainable urban design. Local councils, for example, play a vital role in disseminating information and engaging residents in sustainability initiatives. However, studies have shown that there is often a lack of effective communication between councils and communities, which can hinder engagement efforts [58]. Therefore, developing clear communication channels and utilizing various platforms to share information about sustainable practices and initiatives can significantly enhance community participation [59].

Furthermore, the role of educational institutions in promoting community engagement cannot be overstated. Higher education institutions (HEIs) can serve as catalysts for sustainability by developing policies that encourage community engagement and integrating sustainability into their curricula [60]. By fostering partnerships with local communities, HEIs can facilitate knowledge exchange and empower residents to participate in sustainability initiatives actively [61]. This educational approach not only raises awareness but also equips community members with the skills and knowledge needed to engage effectively in sustainable urban design processes.

Engaging the public in understanding the benefits of sustainable urban design, particularly in urban parks, is essential for encouraging participation in green initiatives. By integrating community input, leveraging technology, and employing effective communication strategies, urban planners can create inclusive and sustainable urban environments that reflect the needs and aspirations of the community. This collaborative approach not only enhances the effectiveness of sustainability initiatives but also empowers residents to take an active role in shaping their urban landscapes.