Quantifying the cooling effects of blue-green spaces across urban landscapes: A case study of Kathmandu Valley, Nepal

Abstract

Mitigating extreme heat is crucial for enhancing the livability and sustainability of urban centers in the face of rising temperatures. A sound understanding of temperature variation is necessary to effectively design heat mitigation strategies. In this study, we develop a framework to quantify the cooling effects of blue-green spaces, such as urban forests, parks, and ponds, through the integration of remote sensing and geo-spatial modeling. We then employ the framework across urbanized, transitional, and vegetation-dominated zones in the Kathmandu Valley, Nepal. Across the valley, our results reveal distinct cooling signatures for each type of natural entity, with urban forests exhibiting the greatest cooling potential (up to 1.2 °C reduction), followed by urban parks (0.9 °C) and ponds (0.85 °C). This hierarchical cooling effect can be attributed to the complex interactions between these features and urban heat transfer processes: forests provide more effective barriers against lateral heat movement through their dense canopy structure and multiple vegetation layers, while also maximizing evapotranspiration cooling; parks offer varying degrees of cooling based on their vegetation density and composition; and ponds, while effective through evaporative cooling, are more susceptible to heat absorption from surrounding urban surfaces. Notably, the cooling efficiency of these blue-green spaces is significantly influenced by their size and the surrounding urban context, with the greatest cooling benefits observed in vegetation-dominated zones. However, in highly urbanized areas, the cooling potential of these blue-green spaces is diminished, underscoring the need for context-specific heat mitigation strategies. Our findings highlight the importance of strategically integrating natural entities' size and location into urban planning zoning, plans, and policies to maximize their cooling benefits and offer valuable insights for urban planners worldwide as they strive to enhance resilience. Future research should focus on developing cost-effective implementation strategies and quantifying additional co-benefits of blue-green infrastructure beyond temperature reduction.