A remote sensing-based assessment of biomass carbon global temporal trends in urban forests

Urban forestation projects are being initiated to mitigate environmental issues, enhance climate change adaptation, and improve urban sustainability. In this study, we used Google Earth Engine (GEE) and Carnegie-Ames-Stanford Approach model (CASA) to evaluate the biomass carbon storage in 40 case cities with large-scale forestation projects. In 2010 and 2020, closed forests in cities of the tropical zones had the highest biomass carbon storage. Each of the three forestation patterns in the case cities - afforestation, reforestation and integrated (afforestation and reforestation) forestation - was orientated based on available local green space and urbanization trends. The study introduced refined carbon accumulation parameters based on climate zones and tree crown cover, generating a high-resolution spatial map of annual biomass carbon accumulation. From 2010 to 2020, the annual biomass carbon accumulation for urban forests (UFs) was 5.84 × 10⁷ tC yr⁻¹, equivalent to 0.58 tC ha⁻¹ yr⁻¹. The results can be used to assess the role of UFs in the carbon balance and mitigation of urban climate change. It can also provide guidance to urban planners in prioritizing the expansion of forestation areas and tree canopy cover for sustainable urban development, in accordance with climate and urban development conditions.