Unraveling the Anthropogenic Impact and Environmental Stress on Net Primary Production of Urban Green Spaces in Singapore

To date, photosynthesis by plant communities remains a widely applicable and feasible carbon sequestration method that helps offset some unavoidable greenhouse gas emissions. However, most research on this nature-based climate solution focuses on natural green spaces rather than urban green infrastructure. Further, large-scale and longitudinal studies are lacking, especially outside temperate regions. This research aims to study how environmental stress caused by the urban environment affects the carbon sequestration capacity of urban green spaces, contributing to a more thorough estimation of the carbon budget in the inventory reports and enlightening better design and management plans for enhancing the capacity, as a path to carbon neutral in the climate action plans. The research utilizes the classic CASA model to calculate Singapore's net primary production (NPP) with cloud-free mosaic Sentinel data from 2021 to 2024 to face cloud coverage challenges. Propensity score matching based on canopy height and soil type matches urban green spaces within 800 meters from their boundaries with green spaces further away with less intervention, and the research calculates their difference in NPP, reflecting the anthropogenic impact. The results show that the duration of shading by buildings, the density of surrounding residential units, restaurants, food centers, and power plants, proximity to roads and waterbodies, percentage of surrounding impervious land, mean land surface temperature around, and traffic flow can explain 68% of the difference between actual and potential carbon sequestration. The duration of shading is the most evident anthropogenic factor, which decreases urban green infrastructure's carbon sequestration capacity, followed by surrounding land surface temperature. The research provides quantitative evidence of anthropogenic impacts on urban NPP in tropical cities with causal inference. Combined with further microclimate and plant species studies, the research would offer detailed planning and design strategies to relieve anthropogenic stress and increase carbon sequestration for urban green spaces.