Urban land use and the heat island effect

Abstract

Higher urban temperatures, driven by the urban heat island (UHI) effect, have several negative health and economic implications such as heat stroke and higher air conditioning usage. The UHI is linked to urban land use. With India’s urban population set to increase to 877 million by 2050, it becomes important to manage land use change in cities to mitigate the UHI effect. In this thesis, we study the local cooling impacts of urban green spaces (UGS) and build a land use change model to help urban policymakers design appropriate green space conservation policies. In our first study, we use high-resolution Landsat and Google Earth data and integrate it with spatial statistical analysis to quantify the cooling provided by UGS in their local neighborhoods. Our analysis of 262 UGS in Bengaluru shows that the average UGS provides cooling effects up till a distance of 347 m (95% CI: 318 m to 376 m) beyond its boundary. The average UGS is 2.23°C (95% CI: 2.13°C to 2.33°C) cooler than the point where it ceases to provide cooling effects. We find that cooling effects reduce with distance from the UGS, and are impacted by the greenness, size, and shape of the UGS. In our second study, we analyse land use change in Bengaluru from 2001 to 2017 to show that the average built-up area is now farther away from a green space, thereby reducing the average cooling it receives. We use a neural network approach to build a spatially explicit land use change model for Bengaluru and forecast urban growth till 2025 under different policy scenarios. Our model has reasonable accuracy with a kappa value of 0.79 in the validation phase. Our analysis shows that policies should protect green spaces that are closest to built-up areas to increase the average cooling provided by UGS to urban populations. The thesis points to the importance of land use in mitigating the UHI and provides a method for using spatial analysis techniques for urban policymaking. Study 1 is among the first to quantify the cooling impacts of UGS at the local neighbourhood level for a large Indian city. When combined with policy scenarios, the land use change model enables policymakers to simulate the potential impacts of land use policies.