Alarming loss of urban greenery revealed in new models

Trees, shrubs, and other greenery lining city streets are essential for creating healthier, more climate-resilient urban environments. They cool neighborhoods during heatwaves, absorb air pollution, support mental health, and even reduce carbon in the atmosphere.

But while these benefits are widely acknowledged, scientists have struggled to consistently monitor how street-level vegetation is changing – especially in fast-growing cities across the world.

A new study led by Giacomo Falchetta of the International Institute for Applied Systems Analysis (IIASA) introduces a breakthrough method for keeping tabs on urban green spaces.

The researchers used satellite imagery and machine learning to monitor how much vegetation exists along city streets and how that is shifting over time.

A global view of green

“Our aim was to develop a method to monitor how much green infrastructure exists along streets and how it changes over time,” said Falchetta.

“Street greenery has well-documented benefits – it reduces urban heat, improves mental health, and can also absorb carbon. But until now, it’s been difficult to track it globally in a consistent and timely way.”

To tackle this issue, the team built a machine learning model to estimate what’s known as the Green View Index (GVI), a measure of how much greenery is visible from a pedestrian’s point of view.

The model was trained on labeled street-level images from cities around the world and then applied to satellite data collected between 2014 and 2022. In total, the researchers assessed 190 large urban areas across 20 global regions.

A subtle but significant decline

The findings show that, on average, cities around the world are losing street-level greenery at a rate of 0.3 to 0.5% per year. Although these numbers may sound small, over time they add up. This is especially true in areas where temperatures are rising and green spaces are already limited.

Some regions are seeing even steeper declines. Urban areas in Asia and Oceania showed the most rapid losses, with median drops in street greenery of 1.7% and 2.6% per year, respectively.

By contrast, cities in Europe and North America showed modest gains of around 1% annually. Cities in Africa and Latin America exhibited smaller and more inconsistent changes.

Trees aren’t shared equally

“Not only is greenery decreasing in many places, but it’s also distributed unequally,” said senior author Ahmed Hammad, a scientist at Decatab PTE LTD in Singapore. “In many cities, green space is sparse where people live.”

“This disparity raises serious questions of fairness and access, especially as heatwaves and other climate stressors intensify.”

Urban greenery is not just a luxury – it’s a form of public infrastructure with life-saving potential. Yet in many cities, wealthier neighborhoods are noticeably greener. Climate impacts hit lower-income communities harder, leaving them with fewer trees and less shade.

A tool for every city

The strength of the new monitoring method lies in its scalability and accessibility. Anyone – from local governments to international agencies – can use the model and update it in real time using free Sentinel-2 satellite data and climate records.

City planners can combine GVI data with indicators like energy use, health outcomes, and temperature trends to target greening efforts more effectively.

The model provides real-time updates and is open-source. Moreover, it supports smart, data-driven decisions for greening cities in ways that are both effective and equitable.

Planning for a greener future

The research aligns closely with the United Nations Sustainable Development Goals – particularly Goal 11, which focuses on building sustainable cities and communities.

As climate impacts grow, authors say cities must prioritize protecting and expanding green infrastructure in urban planning.

“Our results can support targeted greening policies,” Falchetta explained. “With climate extremes on the rise, ensuring equitable access to green space is more urgent than ever. Our work can be a valuable resource for cities to make more informed, just, and targeted greening decisions.”

In a time of rapid urbanization and climate uncertainty, cities need tools to help them grow sustainably. This new approach to monitoring street greenery offers not only a snapshot of where we stand today – but also a roadmap for a more resilient, equitable, and green urban future.

The study is published in the journal Environmental Research: Infrastructure and Sustainability.

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