Think trees only cool roads? Singapore's million-tree plan could slash your AC bill, what scientists discovered
A key figure cited in Singapore’s planning documents and public discourse is that shading a street with trees can lower street-level temperatures by up to 2.6 degrees Celsius.
- Aug 7, 2026,
- Updated Aug 7, 2026 9:00 AM IST
Singapore is planting one million trees across its streets as part of an ambitious urban greening drive aimed at tackling rising temperatures in the tropical city-state. While the initiative is widely promoted for its street-level cooling benefits, scientists now say the most significant impact could be on household and commercial air-conditioning bills.
The 2.6°C Claim and Its Origins
A key figure cited in Singapore’s planning documents and public discourse is that shading a street with trees can lower street-level temperatures by up to 2.6 degrees Celsius. However, this number was not derived from local measurements. It traces back to a 2013 study by Sten Gillner and colleagues in Dresden, Germany, which found that trees with dense foliage and high transpiration rates produced the strongest cooling effect on surrounding air.
In Singapore's own context, official guidance on vegetation around buildings—specifically the "Strategies for Cooling Singapore", a catalogue of 86 heat mitigation measures compiled for policymakers by the Cooling Singapore project, a collaboration between the Singapore-ETH Centre, SMART, TUMCREATE and the National University of Singapore—estimates cooling from tree-shaded streets at between 0.9 and 2.6 degrees Celsius, set against an urban heat island effect that averages about 4 degrees and can exceed 7 degrees during certain hours.
What Singapore Studies Actually Found
In December 2024, researchers led by Lei Xu and Ronita Bardhan published findings in Science of the Total Environment based on 20 paired sites across Singapore, comparing sunlit and shaded locations during a very hot afternoon. Their measurements showed that all forms of shade—trees, bus shelters, awnings, and building shadows—reduced heat stress.
While the drop in raw air temperature was modest (close to 1 degree), the effect on perceived heat was far greater. Using the Universal Thermal Climate Index—which accounts for radiant heat, humidity, and air movement—the study found shade reduced the index by an average of 3.1 degrees. In areas with around 80% coverage from canopy or built structures, the estimated cooling potential reached 3 to 5 degrees.
The Real Savings: Shading Buildings, Not Just Streets
The most detailed attempt so far comes from Naika Meili and co-authors, published in the Journal of Advances in Modelling Earth Systems in March 2025, which combined a building energy model with an urban ecohydrological model to simulate tree cover scenarios across seven hot cities worldwide, including Singapore.
The study’s central finding was that electricity savings come primarily from shade falling directly on buildings—their walls and windows—rather than from any reduction in outdoor air temperature. For hot, humid cities like Singapore, modelled summer cooling energy savings averaged 6 to 9 per cent. This is notably lower than the roughly 17 per cent modelled for drier cities like Riyadh and Phoenix.
The reason: in humid climates, trees release moisture into the air, and removing that extra humidity during dehumidification consumes additional power. The benefit peaks at around 40 per cent tree cover before added humidity begins to offset savings. Still, trees trimmed electricity demand most sharply during peak afternoon hours—a critical detail for grid operators.
Why the Shade Has Limits
Shade is not without trade-offs. A meta-analysis of 182 separate studies, published in Communications Earth and Environment found that tree canopy performing well during the heat of midday can trap outgoing radiation after dark, holding heat closer to pedestrian level overnight in dense, high-rise urban areas. The Cooling Singapore catalogue also notes that dense planting placed within a natural wind corridor can act as an unintended windbreak, which matters in a city where average wind speeds already sit below 3 metres per second, making the loss of a cooling breeze a real cost in exchange for shade.
Singapore is planting one million trees across its streets as part of an ambitious urban greening drive aimed at tackling rising temperatures in the tropical city-state. While the initiative is widely promoted for its street-level cooling benefits, scientists now say the most significant impact could be on household and commercial air-conditioning bills.
The 2.6°C Claim and Its Origins
A key figure cited in Singapore’s planning documents and public discourse is that shading a street with trees can lower street-level temperatures by up to 2.6 degrees Celsius. However, this number was not derived from local measurements. It traces back to a 2013 study by Sten Gillner and colleagues in Dresden, Germany, which found that trees with dense foliage and high transpiration rates produced the strongest cooling effect on surrounding air.
In Singapore's own context, official guidance on vegetation around buildings—specifically the "Strategies for Cooling Singapore", a catalogue of 86 heat mitigation measures compiled for policymakers by the Cooling Singapore project, a collaboration between the Singapore-ETH Centre, SMART, TUMCREATE and the National University of Singapore—estimates cooling from tree-shaded streets at between 0.9 and 2.6 degrees Celsius, set against an urban heat island effect that averages about 4 degrees and can exceed 7 degrees during certain hours.
What Singapore Studies Actually Found
In December 2024, researchers led by Lei Xu and Ronita Bardhan published findings in Science of the Total Environment based on 20 paired sites across Singapore, comparing sunlit and shaded locations during a very hot afternoon. Their measurements showed that all forms of shade—trees, bus shelters, awnings, and building shadows—reduced heat stress.
While the drop in raw air temperature was modest (close to 1 degree), the effect on perceived heat was far greater. Using the Universal Thermal Climate Index—which accounts for radiant heat, humidity, and air movement—the study found shade reduced the index by an average of 3.1 degrees. In areas with around 80% coverage from canopy or built structures, the estimated cooling potential reached 3 to 5 degrees.
The Real Savings: Shading Buildings, Not Just Streets
The most detailed attempt so far comes from Naika Meili and co-authors, published in the Journal of Advances in Modelling Earth Systems in March 2025, which combined a building energy model with an urban ecohydrological model to simulate tree cover scenarios across seven hot cities worldwide, including Singapore.
The study’s central finding was that electricity savings come primarily from shade falling directly on buildings—their walls and windows—rather than from any reduction in outdoor air temperature. For hot, humid cities like Singapore, modelled summer cooling energy savings averaged 6 to 9 per cent. This is notably lower than the roughly 17 per cent modelled for drier cities like Riyadh and Phoenix.
The reason: in humid climates, trees release moisture into the air, and removing that extra humidity during dehumidification consumes additional power. The benefit peaks at around 40 per cent tree cover before added humidity begins to offset savings. Still, trees trimmed electricity demand most sharply during peak afternoon hours—a critical detail for grid operators.
Why the Shade Has Limits
Shade is not without trade-offs. A meta-analysis of 182 separate studies, published in Communications Earth and Environment found that tree canopy performing well during the heat of midday can trap outgoing radiation after dark, holding heat closer to pedestrian level overnight in dense, high-rise urban areas. The Cooling Singapore catalogue also notes that dense planting placed within a natural wind corridor can act as an unintended windbreak, which matters in a city where average wind speeds already sit below 3 metres per second, making the loss of a cooling breeze a real cost in exchange for shade.