Estimating impacts of micro-scale land use/land cover change on urban thermal comfort zone in Rajshahi, Bangladesh: A GIS and remote sensing based approach

Abstract

Rapid urban growth causes significant decrease in green cover which ultimately results higher temperature and strongest Urban Thermal Field Variance Index (UTFVI) effect. Rajshahi has the highest heat index score after the southwest region. Hence, Rajshahi city is particularly vulnerable to heat waves. There is a major gap in exploring the micro-scale thermal conditions in Rajshahi. The primary purpose of this study is to evaluate urban ecological health in the four major urbanized zones of Rajshahi City Corporation (RCC) area namely, City Centre, Eastern Fringe, Western Fringe and Northern Fringe over the past three decades (1992–2022). Land Use/Land Cover (LULC) variations, ecological balance, and their effects on the thermal environment at various scales have all been extensively analyzed using an integrated approach of geographic information systems (GIS) and remote sensing (RS). Landsat satellite images with a 30 m spatial resolution were used to carry out this micro-scale study. In ENVI 5.3 software, the Support Vector Machines (SVM) algorithm was used for its accuracy and popularity in image classification. Images from the past three decades were classified at five-year intervals using SVM, relying on specific training procedures. Four land cover indices are utilized to assess the geographical and temporal differences in Land Surface Temperature (LST) caused by land cover. Statistical relationship between various land cover indices and LST was performed using Statistical Package/Program for Social Sciences (SPSS). The overall increase of urban area during the study period was 53.61 %, resulting in a concentration of 28.09 km² of urban area (58.45 %) in 2022 from 2.32 km² (4.83 %) of 1992. The directional analysis of Thermal Comfort Zone (TCZ) reveals a significant decrease of thermal comfort environment due to loss of green space in NE to NW region during the study period. The regression analysis among LULC and LST revealed significant negative relation (p < 0.05) for water body and vegetation cover while the relationship is positive for urban area which concluded that urban centres experienced the most substantial LST increases, as evidenced by the study's observation of a substantial increase in higher temperature zones. This urban encroachment, which is influenced by factors such as population growth and economic development, has resulted in a reduction in comfortable thermal zones, which has exacerbated the urban heat island effect and impacted the ecological sustainability of urban areas. By avoiding concentrated impermeable surfaces, such as built-up areas, and boosting green cover, urban development can effectively mitigate the effects of LST and UTFVI. Again, effective distribution of LULC can play a crucial role in mitigating the effects to a significant extent. The findings of this study reflect the necessity of proper sustainable solution through the successful implementation of urban planning techniques which would help urban planners and policymakers to create effective strategies in order to ensure comfortable thermal environment.