# Will cities keep getting hotter? The interplay of urban expansion and greening reshapes future urban heat trajectories

## TL;DR

This study shows how urban expansion and greening efforts together shape future urban heat patterns, revealing that cities may not always get hotter in the same way.

## Contribution

A novel framework classifies urban areas into four development pathways based on impervious surface and vegetation trends, revealing complex UHI dynamics.

## Key findings

- Urbanized centers often greened, while urbanizing suburbs browned, but 30% showed the reverse pattern.
- Greening initiatives reduced UHI in urban centers and limited UHI growth in suburbs.
- Urban expansion and browning increased suburban temperatures, flattening the classic urban-to-rural UHI gradient.

## Abstract

Urban heat islands (UHIs) pose growing risks to public health, infrastructure, and resilience. While often assumed to intensify with urban growth, dynamic changes in urban expansion and vegetation greenness complicate UHI trajectories, which remain poorly understood. This study investigated the interplay of urban expansion and greenness change on UHI spatial profile across 36 Chinese megacities during 2003–2018 using multiple satellite products. We introduce a framework that classifies urban areas into four dynamic development pathways based on impervious surface area (ISA) and enhanced vegetation index (EVI) trends: urbanized-greening, urbanized-browning, urbanizing-greening (UingG), and urbanizing-browning (UingB). While most urbanized centers exhibited greening driven by targeted initiatives and urbanizing suburbs showed browning due to vegetation loss, about 30% urban areas showed the reverse pattern, revealing overlooked complexity in urban development. Urban expansion and browning strengthened UHI in suburban areas, whereas greening initiatives mitigated UHI in urban center and mitigated UHI enhancement in suburban areas. Slowed warming in urban centers together with accelerated warming in suburban areas flattened the temperature gradient between urban centers and suburbs. This dynamic expanded the spatial extent of elevated temperatures and reshaped the classic urban-to-rural UHI profile into a flatter form. In UingB areas, UHI intensification was jointly driven by increase in ISA, vegetation loss, and their interaction, while in UingG areas, EVI increases and a negative interaction together offset over half of the warming driven by urban expansion. These findings reveal that UHI evolution is not unidirectional but depends on localized urbanization and greening dynamics, offering pathways for strategic heat mitigation.