Urban forests, parks, and ponds could lower Kathmandu’s temperature by as much as 1.6°C if implemented strategically, according to a new study published in the journal Urban Climate. The research represents the first of its kind to closely examine how different types of blue-green spaces help cool down areas across the Kathmandu Valley.

The study, carried out by an international team from seven institutions, looked at 301 parks, 130 urban forest patches, and 26 ponds within the valley’s high-density urban areas using satellite-based information and Machine Learning algorithms. The study shows that Swoyambhu forest stayed cooler at 31.9°C, while nearby city areas reached 36.0°C—a difference of 4.1°C. At UN Park, the temperature was 34.3°C, compared to 38.2°C in the surrounding buildings, a difference of 3.9 °C. A traditional pond, Na Pukhu, in Bhaktapur measured 39.6°C, while the nearby urban area hit 42.5°C, the study found. 

The number represents the highest cooling effects recorded over five summers, highlighting how much these blue-green spaces can help during the hottest times. It is important to note that the satellite temperature estimates give an idea of the ground temperatures but still need to be confirmed with actual measurements on the ground. However, the differences they show help us understand important cooling patterns.

Overall, urban forests provide the greatest cooling effect, lowering temperatures by up to 1.2°C on average. Parks come next, cooling by up to 0.9°C, and ponds can reduce temperatures by up to 0.85°C.  But how well these spaces cool depends a lot on their surroundings. In vegetation-dominated areas, blue-green spaces can cool temperatures by as much as 1.6°C, while in densely built areas, the cooling effect drops to just 0.3-0.6°C. 

Lead researcher Saurav Bhattarai, a PhD student at Jackson State University, USA and an ORISE fellow, said the findings show that effective cooling strategies should be tailored to specific urban contexts. “Just adding green spaces is not enough; they need to be carefully designed and well integrated with the surrounding city environment,” he explained.

This study comes at a time when the Kathmandu Valley is getting steadily warmer, with temperatures rising by 0.38°C per decade since 1976. 

The study also found that soil moisture in the valley has dropped by an average of 2.1 percent over the past decade, with some central urban areas experiencing reductions as high as 35 percent.

Dr Rocky Talchabhadel from Jackson State University stressed the need for urgent action. “Our study shows that Kathmandu’s high-density areas are at greater risk from extreme heat. Without immediate action, these urban heat islands will only get worse,” he said.

Urban forests demonstrated the strongest relationship between their size and cooling effect—when the forest area doubles, the cooling effect increases by about 30 percent.  Parks showed moderate connection between size and cooling, but how well they cool depends more on how they are designed inside, not just their size. 

Park landscape design reveals that tree canopy coverage proves most critical for cooling effectiveness. In small parks, a one percent increase in high canopy area corresponded to an approximate 0.99°C increase in cooling effect. For the largest parks, high canopy coverage demonstrated substantial impact, with a one percent increase linked to a 1.76°C increase in cooling effect.

Prof Vishnu Prasad Pandey from Tribhuvan University noted that strategic placement and design of blue-green spaces can maximize cooling benefits even in space-constrained urban areas. “This isn’t just about planting more trees. The internal composition of parks—the ratio of tree canopy, grass and impervious surfaces—determines their cooling effectiveness more than their size alone,” he said.

The research team recommends different approaches for different urban zones. For dense urban cores, priority should be given to water features and rooftop solutions, including cisterns, reflective pools, green roofs and rooftop farming, while safeguarding existing mature trees. For transitional areas, the focus should be on expanding forest patches and designing parks with high, contiguous tree-canopy cover to maximize shade. In vegetation-dominated zones, conservation of current forests and green buffers can prevent future urban heat island formation.

Dr Prajal Pradhan from the University of Groningen, Netherlands, stressed the global applicability of the findings and methods. “Cities globally can learn from our findings based on the Kathmandu Valley. We provide a framework for assessing cooling potential that can be applied anywhere and used to plan cities to adapt to urban heat,” he said.

Dr Nawa Raj Pradhan from the US Army Engineer Research and Development Center warned that if no action is taken, increasing temperatures will put pressure on public health systems, increase energy demands for cooling and disproportionately hit vulnerable communities the hardest. The study estimates that implementing comprehensive cooling strategies could reduce urban cooling energy demands by 15-25 percent, potentially saving significant electricity costs while improving public health outcomes.