نوع مقاله : مقاله پژوهشی
موضوعات
عنوان مقاله English
نویسندگان English
Aim: This research aims to reveal the expansion trend of the built-up up of Khorramabad city and its effects on the boundary layer height and surface albedo in the city.
Material & Method: The data related to the 2 main factors as surface Albido (FAL) and boundary layer height (BLH), were also obtained from the ECMWF data of ERAS model for the statistical period of 1990-2020.
Finding: The results indicated that the urban area of Khorramabad grew by 829 hectares during the 30-year period, which indicates that this city expanded by 47% during the last 30-year period. The climatic result of this physical expansion in 2 variables of surface albedo and boundary layer height represented that with the expansion of the physical built-up of the city, the amount of albedo has decreased significantly. This decrease in surface albedo has caused a further increase in radiation and an increase in the heat budget of the city, which has increased the height of the boundary layer during the statistical period of 1990-2020.
Conclusion: The expansion of Khorramabad's physical built-up has significantly reduced the surface Albido and increased the height of the boundary layer in the city.
Innovation: Investigating and revealing the effect of land use changes on the thermal factors of the lower atmosphere of the region (surface albedo, boundary layer height) is the most important innovation of this research. Changes in thermal factors such as albedo and boundary layer height have extensive effects on climatic comfort and environmental quality. Therefore, it is essential to reveal the impact of the physical texture of the city concerning the spatial distribution, green space and urban gardens and parks to adjust the city's thermal conditions.
کلیدواژهها English
Urbanization changes natural landscapes to manufactured uses and changes the surface with different physical characteristics. Changes and transformations in surface coverings have an important effect on the local weather conditions, population, and building densities, along with heat production caused by human activities, which constantly change the shape of cities, and the decrease in the visibility of the sky causes an increase in the temperature of the city compared to the surrounding environment. With the majority of the world's population living in cities, it is essential to investigate whether urban areas can be the cause of unprecedented climate change in the last century. Today, one of the most important challenges for societies and institutions is the adaptation of urban areas to atmospheric and climatic changes. The effect of urbanization on atmospheric changes and its boundary layer manifests itself in the form of phenomena called heat islands, which have more heat flux than their surrounding environment. The important feature of heat islands is the increase in air temperature in urban environments compared to the surrounding areas and suburbs. Much evidence shows the mutual relationship between the atmosphere and land cover, the physical feedback of land cover or land use to the amount of radiation received in the form of its reflection in the wavelength or appears in long infrared. Surface albedo is a fraction of the sun's short-wave radiant energy reflected by the Earth's surface in all directions. Albedo is a critical physical parameter in climatic and meteorological studies, hydrological studies, and studies in radiation transfer and calculation of the Earth's radiation reserve. The albedo of the Earth's surface depends on the characteristics and type of land cover, weather conditions, soil moisture level, and vegetation in the area. The main goal of this research is to reveal the process of physical changes in Khorramabad and recover their effects on the two climatic components of boundary layer height and surface albedo in Khorramabad.
In this article, two types of data have been used. The first data set is related to Landsat 5 and 8 satellite images for 4 statistical periods with 10-year time steps of 1990, 2000, 2010, and 2020 for June with the minimum cloudy or cloudless filter. Considering that Khorramabad city is located in the 39th zone of the UTM coordinate system, a Landsat image block with the coordinates of 037 Row and 166 Path for 4 years 1990, 2000, 2010, and 2020 was obtained from the Earth Explorer database for June of this year.
The second group of data was related to the two climatic factors, surface albedo 2 (FAL) and boundary layer height 3 (BLH). These data were also obtained from the comprehensive database of Copernicus from the ECMWF collection, ERA5, with Netcdf format and a spatial resolution of 0.12 arc degrees, separating the two warm (June) and cold (January) seasons of the year for the statistical period 1990-2020. The surface albedo product of ERA5 reanalysis is a dimensionless index showing the surface reflectance level. However, the height of the boundary layer is a calculation index in meters (height above the ground).
This research aims to reveal the effect of the expansion of the physical fabric of Khorramabad city on two climatic/meteorological factors, including the surface albedo and the height of the boundary layer. In this regard, first, a 30-year trend of two climatic/meteorological factors, i.e., surface albedo and height of the boundary layer of the cold and warm periods of the year (January and June were chosen as representative of the cold and warm periods of the year) using two flow analysis tests The non-parametric Sen slope estimator and the Man-Kendal test are performed at a confidence level of 0.95 (P_value=0.05).
Land cover classes or land use is one of the most important shapers and determinants of the climate near the surface of the earth. The role of land cover in the received radiation budget has a significant impact on determining the temperature of the surface of the earth, soil moisture, phenological phases of a plant and surface biodiversity. One of the most important motives and drivers of climate change are land cover and land use changes, especially urban and residential physical development in natural lands and areas. In this research, it was seen that the analysis of the physical changes in the urban fabric of Khorramabad using Landsat 5 and 8 satellite images during the statistical period 1990-2020 indicated that the urban context of Khorramabad has faced a growth of 829 hectares during this 30-year period, which indicates that the city of Khorramabad has expanded by 47% during this 30-year period. The increasing trend in the growth of the area or urban use in Khorramabad is a model that has been seen in most cities of the country (Heydari et al., 2023, Safarrad et al. 2023). This expansion was generally in lands with thin vegetation and pastures or agricultural lands and gardens. The microclimatic result of this physical expansion of Khorramabad city can be recovered in two climatic variables as surface albedo and boundary layer height. The investigation and revealing of the relationship between the decadal changes in the urban fabric of Khorramabad by two climatic factors, namely surface albedo and surface temperature, indicate a significant relationship, as observed in similar studies such as Safarzadeh et al., 2019, Heidari et al., 2023. The results of the correlation analysis between the temporal trend of urban changes in Khorramabad and the values of surface albedo of this city during the statistical period of 1990-2020 showed that both in cold and warm years, there has been a significant inverse correlation, at a confidence level of 95% (P_value=0.05), between changes in surface albedo and urban texture changes in Khorramabad. This negative correlation indicates that concurrently with the growth and development of the urban fabric, the albedo or surface reflectance has decreased, and the absorption of radiation by the urban fabric has increased. This pattern of relationship was more pronounced during the cold years. The effect of a reduction in surface albedo can be restored by changing the thermal regime of the city. On the other hand, the relationship between the development process of the physical texture of Khorramabad city and the changes in the height of the border layer in Khorramabad city has been significantly high. This direct correlation indicates that with the physical development of Khorramabad city during the period of 1990-2020, the height of the boundary layer on the surface of Khorramabad city has also increased. This level of correlation between the expansion of the Khorramabad urban texture and the height of the boundary layer has been higher in the cold period of the year. Based on this, it can be said that the expansion of the urban texture of Khorramabad has, on one hand, led to a decrease in surface albedo in the city and, on the other hand, resulted in an increase in the boundary layer height, with this pattern being stronger during the cold years. Thus, based on a futuristic perspective, it can be postulated that with the continuation of the urban texture expansion trend in Khorramabad, its climatic effects may lead to a warmer urban environment. In this regard, attention to green space per capita and appropriate distribution and proportion of green space at the city level to mitigate the city's climatic conditions is very important.
The results of the analysis of the urban texture changes in Khorramabad, using Landsat 5 and 8 satellite images during the statistical period of 1990-2020, showed that the urban texture of Khorramabad has experienced a growth of 829 hectares during these 30 years, indicating a 47% expansion of the city. The climatic outcome of this urban expansion in Khorramabad, in terms of two climatic variables, surface albedo and boundary layer height, indicated that with the expansion of the urban texture in Khorramabad, the surface albedo in the city has considerably decreased. The decrease in the amount of surface albedo has caused more radiation absorption and increased the city's thermal budget. The result of this increase in the thermal budget of the city is an increase in the height of the boundary layer during the statistical period of 1990-2020 in the level of Khorramabad city. Based on this, the expansion of the physical texture of Khorramabad during the statistical period of 1990-2020 has notably led to a decrease in the surface albedo and an increase in the height of the boundary layer in the city.
