Analysis of thermal comfort of settlements based on urban humidity index in Yogyakarta City

Increasing urban development has led to an increase in land use, particularly in settlements. The massive and uncontrolled growth of settlements can lead to a decrease in the quality and thermal comfort of the settlements. Yogyakarta is one of the cities in Indonesia with rapid development and population growth. This study aims to analyse the quality and thermal comfort of settlements in Yogyakarta city. The remote sensing data used is Landsat 8 OLI image for the analysis of vegetation index, land surface temperature, and urban heat island (UHI). The results of the model are presented in the form of maps so that the spatial pattern of UHI can be identified and correlated with the comfort level calculated using the temperature humidity index (THI). Based on the results of the data analysis conducted, it is known that the analysis of thermal comfort in the city of Yogyakarta is dominated by the comfortable class (97%), uncomfortable class (3%), and very uncomfortable class (0%).


Introduction
Cities are environments resulting from human modification that develop due to the urbanization process.Cities in developing countries are largely influenced by rapid urban growth.The increase in the number of urban residents is directly proportional to the increase in pollutants in the air which causes urban air temperatures to be higher and more uncomfortable than the surrounding areas [1].The increasing temperature in urban areas and decreasing humidity can reduce the level of comfort in urban areas.Therefore, the existence of urban green space is very important in creating a cool and comfortable environment [2].Urban green space is vegetative land in urban environments, residential gardens, parks, trees and other natural areas [3][4][5][6][7].
The city of Yogyakarta is one of the cities in Indonesia with very rapid development and population growth.Yogyakarta's predicate as a student city and cultural city makes Yogyakarta one of the migration destinations for people.The increasing population has resulted in very high urban energy needs in Yogyakarta due to the large amount of built-up land [8].Buildings contribute to increasing urban temperatures because the thermal properties of building construction materials enable faster heat transfer [9].The increasing need for land in the City of Yogyakarta causes higher pressure on land conversion and land use, especially conversion into new residential areas.Higher land prices and narrowing urban open space led to an increase or density of buildings, the construction of slums and illegal settlements as well.The addition of uncontrolled new settlements can cause a decrease in the quality of settlements and an increase in temperature conditions [10].The thermal comfort of settlements is one aspect that becomes part of residential comfort.Thermal comfort is obtained through measurement of air temperature and relative humidity.a thermal comfort settlement can be assessed through the Temperature-Humidity Index (THI).THI is a single value representing the combined effect of temperature and humidity related to the level of thermal stress.This index has been developed as a weather safety index to monitor and mitigate pressure losses heat [11].Heat stress is caused by a combination of environmental factors (temperature, relative humidity, solar radiation, air) movement, and rainfall).Many indices incorporate these environmental factors different to measure the degree of heat stress [12].From the THI method an index can be generated to determine the effect of hot conditions on human comfort combined temperature air and air humidity.
This study aims to examine the thermal comfort in the residential environment of the city of Yogyakarta physically by measuring meteorological parameters and social aspects by knowing people's perceptions of thermal comfort in their homes.

The Method of The Research
Previous research conducted in 2020 showed that vegetation has an effect on reducing land surface temperature, The energy demand of Yogyakarta city is very high as indicated by the high urban heat island index value (Sumunar et al, 2020).This year's research is a continuation by analyzing the comfort index of Green Open Space.The research location in Yogyakarta City is geographically located at 110°24′19″ to 110°24′19″ East Longitude and 7°15′24″ to 7°49′26″ South latitude with an average altitude of 114 meters above sea level (Figure 1).
The spatial modeling of city energy is done with several stages, namely Landsat image analysis for land use mapping, vegetation index analysis and calculation of land surface temperature.The primary data used in this research is Landsat 8 image data.Landsat 8 image data.Landsat 8 is a satellite image produced from a joint project between USGS and NASA project between USGS and NASA and NASA Goddard Space Flight Center.
This image records the earth's surface every 16 days, making it possible to be used for monitoring an area on a daily basis.possibleif used for monitoring an area periodically.The spatial coverage of each Landsat pixel is 30 m, with a radiometric resolution of 12 bits.Landsat 8 consists of two instruments Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS).Landsat 8 is used for land cover mapping of the city of Yogyakarta, vegetation index analysis and surface temperature of the city of Yogyakarta.2.1.Settlement Data Quality Analysis.Data analysis of settlement quality is measured through a scoring system obtained by weighting each variable.Settlement density was analyzed at each administrative boundary.Settlement density is obtained through ArcGIS software processing referring to Table 1 and the following equation.--------------------------Administrative area

Analysis of Temperature Humidity Index.
The temperature humidity index is an index with units of degrees Celsius as a quantity that can be related to the level of comfort felt by the human population in urban areas.The comfort limit uses a comfort interval modified for tropical climates, at a THI value between 21-24°C there is 100% of the population stating that it is comfortable, THI between 25 -27°C only 50% of the population feels comfortable, and at THI > 27°C as many as 100% of the population feels uncomfortable.The range of comfort index values in the tropics is in the THI range of 20-26 °C.
The data analysis used is simple linear regression analysis Y = a + b X. Description: Y = dependent variable X = independent variable.The t-test is used to see partially (partial test) whether each independent variable has an effect on the dependent variable, when the other variables are assumed to be constant.Kolmogorov Smirnov test to test whether the assumptions in the simple linear regression analysis are fulfilled.

Correlation of UHI and THI.
The results of the UHI analysis show that the majority of the Yogyakarta City area are at UHI 3 and 4 (Figure 2).The UHI index spread with the highest value is in the downtown area, where the areas with the highest UHI clusters are spread over several sub-districts, namely Gondomanan, Pakualaman, and Kraton, while the smallest UHI is spread in the western region, namely in Tegalrejo District and the eastern part of the border between the Districts Umbulharjo and Kotagede Districts around the Gajah Wong River (Sumunar et al., 2020).
The comfort value is analyzed based on the THI value calculated from the relative humidity and temperature indicators.The results of field data measurements obtained the lowest temperature at the study site, namely 22°C while the highest temperature was 32°C, with an average temperature at all sample points of 28°C.The lowest relative humidity value is at 48% while the highest relative humidity is at 80%.Air temperature and air humidity are the main climate parameters that affect human comfort.The high and low air temperature and humidity greatly affect human comfort in their activities.The humidity indicator shows humidity below 60%, lower than other areas in Yogyakarta City.The Mergangsan area also has a high THI value.From the results of the THI indicator measurements, the temperature in Mergangsan is 32°C with lower humidity than other areas, which is less than 60%.Based on the results of measurements in the field and calculations of THI, it shows that there is a correlation between THI and the two main indicators, namely air temperature and relative humidity.

Correlation of THI with Comfort Level.
The R 2 value of 0.93 indicates that there is a strong positive correlation between temperature and THI.This means that the higher the air temperature, the more uncomfortable it is, and vice versa.Field data shows that there are 26 points in Yogyakarta City that are classified as comfortable, 3 points are in the uncomfortable category, and 2 points are in the very uncomfortable category.The results of the analysis of thermal comfort levels based on the THI value at the research location showed a minimum value of 21.85°C which was in the comfortable category and a maximum value of 35.84°C which was in the very uncomfortable category.
Outdoor thermal comfort levels are generally considered comfortable with a value of less than 27ºC.Conversely humans will tend to feel uncomfortable doing activities at a thermal comfort level of more than 27ºC.Based on the method THI (Temperature Humidity Index) in the city of Yogyakarta obtained the level of thermal comfort in the category of comfortable, and felt in 97% of locations in Yogyakarta, while the remaining 3% enter the region with the category of uncomfortable and very uncomfortable thermally in activities.Distribution of thermal comfort (THI) can be seen in Figure 2 which shows the city of Yogyakarta is in a low THI condition (comfortable) felt in almost all of Yogyakarta except in the district Mergangsan, Gondokusuman, Jetis, and Tegalrejo.Outdoor thermal comfort has a direct effect on the health and well-being of outdoor space occupants (Abdollahzadeh & Biloria, 2021).

Conclusions
Based on the results of the data analysis carried out, it is known that the thermal comfort analysis in Yogyakarta City is dominated by the comfortable class (97%), uncomfortable class (3%), and very uncomfortable class (0%).With the increase in the level of UHI, it shows that the humidity and thermal comfort of the City of Yogyakarta are decreasing.Remote sensing and geographic information systems can be an alternative solution in mapping the level of thermal comfort in urban areas. .

Table 1 .
Classification of Settlement Density Source: Directorate General of Human Settlements