GIS-based spatial simulation of impacts of urban development on changing both land cover area and land surface temperature in Dhaka city

Abstract

Dhaka city is confronted with a big challenge due to significantly high rate of physical and population growth since 1981, which has created tremendous pressure on urban land, utility services, and other amenities of urban life. A substantial growth of built-up areas i.e. urban development is transforming increasingly the landscape from natural cover types to Impervious Surface (IS). It is building up Urban Heat Island (UHT), which has adverse effect on the urban climate change such as abrupt temperature rise, erratic rainfall, degrading air quality. Therefore, Dhaka city is adversely affected by erratic rainfall and heat stress, resulting calamities like flood, water logging, health outbreak, and water scarcity including greenhouse climate changes. A goal of this study is thus set to find out the impacts of urban development on land cover areas (LCA) and land surface temperature (LST) in Dhaka city over the period of 1989 to 2010. To achieve this goal, the study is carried out to assess the relationship between the land surface temperatures (LST) and land cover (LC) area from both quantitative and qualitative perspectives. In this study, the proposed study area is confined to Dhaka Metropolitan Area (DMA). Satellite images of DMA area over the period of 1989 to 2010 is compiled from USGS website as zip format. To conduct this research, two well-known softwares namely ArcGIS 9.2 and Erdas Imagine 9.1 are utilized. Spatial simulation and analysis are carried out using advanced geographic information systems (GIS). Supervised classification methods have been taken to prepare the LC map and LST is derived from the thermal band of Landsat TM/ETM+ using the calibration of spectral radiance and emissivity correction of remote sensing. GIS based spatial simulation has been conducted to establish the relationship of LC and LST. The result shows that category of built-up is grown up to 23.18% in constant growth rate and it was changed from the categories of water bodies and vegetation Land Cover during the period of 1989 to 2010. The changing of LST is directly correlated with LC transition and LST is increasing in those areas where LC of built-up and earth fill or sand categories (urban development) are grown up. In addition, it is also proved from the result that the amount of vegetation (NDVI) is negatively correlated with LST. For that reason, the built-up areas for which NDVI value is greater have been found to have low LST value. Again, the NDBI value is positively correlated with the LST. The trend of LST and LC transition indicates that LST of the Dhaka city will be abruptly increased in near future. The outcome thus obtained from this study would address the future consequences of changing both LCA and LST in Dhaka and would propose a strategic roadmap to reduce LST and UHI as a unique contribution to knowledge-base of scientific community. Moreover, this significantly important research for urban planning would provide supports to decision makers to prepare the planning strategies for the reduction of heat island effect and the quality improvement of urban environment. The urban temperature distribution maps, the analyses of thermal-land cover relationships and the spatial simulated maps of impacts of LST changes can be used as a guideline for urban planning and a smart solution to the reduction of UHI effect. Finally, some strategies are proposed to reduce urban heat islands build-up. On the basis of these research findings, intelligent land use planning for controlling undesirable development, cool roof or green roof for improving the solar reflectance of roofs, conservation of vegetation area and water bodies, guideline for urban geometry are considered as the solution to reduce the LST.