A new study highlights the importance of climate-responsive urban greening strategies that consider humidity and airflow to maximise cooling benefits in Indian cities.
Along with vegetation cover, greenery in urban places should be planned looking at humidity and airflow in order to have a cooling effect, an analysis of 138 cities in India has revealed.
Tree shade is among the fastest ways to make heat more bearable. It cuts direct sunlight, protects people outdoors, and therefore remains essential for heat action plans.
Lead author Angana Borah, research graduate at the Indian Institute of Technology Gandhinagar's department of civil engineering, said findings published in the journal Nature Communications point to a more practical approach to urban greening.
"The question is not whether cities should green. They should. The question is what kind of green, where, and how much," she said.
"In dry cities, vegetation can provide strong cooling benefits. In humid and compact neighbourhoods, planners also need to think about airflow and moisture build-up," Borah said.
Researchers analysed temperature and humidity data recorded during 2003-2020 across tropical savanna, semi-arid steppe, and humid subtropical climates.
Instead of relying only on land surface temperature, the team reconstructed the 'heat index', which combines temperature and humidity and is closer to how heat is felt by the human body.
"Greening is essential for climate adaptation, and shade gives people immediate relief," author Udit Bhatia, associate professor at Indian Institute of Technology Gandhinagar, said.
"Our results show that one-size-fits-all plantation targets miss part of the problem. Cities need greening strategies that are designed for shade, moisture, and ventilation together," Bhatia said.
Green cover is not a single variable -- canopy structure and canopy activity can affect humid heat differently, the researchers said.
They found that vegetation cover and canopy structure were associated with lower model-predicted heat index, but a high canopy activity was associated with a higher heat index in certain settings, with an earlier onset of warming in humid, dense urban cores.
The reason is physical and intuitive -- trees cool through shade and evapotranspiration, the team said.
They explained that in dry air, evapotranspiration can be strongly beneficial because the released moisture evaporates into air that can still absorb it.
However, in humid and compact neighbourhoods, extra moisture can remain trapped near the ground -- the result can be a higher heat index even though shade continues to provide immediate relief at the street level, the researchers said.
The takeaway is not to slow greening, but to make it climate-responsive, they said.
"Vegetation can cool urban environments but can also intensify humidity and thermal discomfort, raising questions about when green adaptation succeeds or backfires," the authors wrote.
The findings "indicate that green adaptation can shift from a cooling asset to a humid-heat liability under some conditions, underscoring the need for climate-responsive and equitable design strategies in the Global South," they said.
People most exposed to dangerous heat often live or work in dense, poorly ventilated neighbourhoods and have limited access to cooling. A better planned greening could help the communities by improving shade while reducing long-term humid-heat stress more effectively, the team said.