The responses of topsoil organic carbon stocks in urban greenspaces to climate change and the urban heat island effect

Goulbourne, Charlie and Quinton, John and Davies, Jessica (2025) The responses of topsoil organic carbon stocks in urban greenspaces to climate change and the urban heat island effect. Masters thesis, Lancaster University.

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Abstract

Urban greenspaces are increasingly recognised as important soil organic carbon (SOC) stores, yet their future dynamics remain uncertain due to unique interactions between climate change, management, and local urban drivers. The N14CP process-based nutrient cycling model, extended to represent urban parkland management, was applied to simulate SOC trajectories in 12 temperate and boreal urban greenspace sites from 2023 to 2100 under four SSP-based temperature scenarios, three nitrogen deposition trajectories, and three levels of urban heat island (UHI) intensity (+0, +1, +2.5 °C). Across sites, the model projected that SOC stocks declined by 6.5% on average under SSP2-4.5 with medium nitrogen deposition, with losses amplified by an additional ~2.5% per +1 °C UHI increment. Nitrogen deposition partially offset declines, but gains were modest and occurred only under low-to-moderate warming in a minority of sites. Site trajectories were heterogeneous, with some sites continuing to accumulate SOC under moderate warming, while others exhibited consistent decline, however, no sites exhibited resilience to warming, and SOC stock sensitivity to warming was consistently negative. The findings of this study also highlight that UHI effects could be of comparable magnitude to differences between global climate scenarios, underscoring the importance of urban cooling strategies to limit SOC stock loss in urban greenspaces. While nitrogen inputs can buffer declines, limited sequestration potential under continued warming and falling nitrogen deposition suggests that urban greenspaces should not be regarded primarily as a mitigation lever but rather integrated into wider carbon budgets and adaptation planning with explicit attention to site history, management, and local thermal regimes.