Advancing our understanding on the climate mitigation potential of urban green infrastructure

Nature based solutions have a critical role in climate mitigation and adaptation in cities. Recently, urban vegetation has gained attention in cities’ climate action plans as a vital strategy for enhancing carbon sequestration from the atmosphere. To support the cities, a detailed knowledge of the strength and variability of urban biogenic carbon sinks and their dependencies on environmental conditions in changing climate is critical. In this study we harness the intensive eco-physiological observations made in parks, gardens, forests and street trees in the Helsinki in 2020—2022 and land surface modelling (LSM) to examine our current capabilities in simulating urban biogenic carbon sinks and the magnitude and variability of these sinks in different urban vegetation types and in changing climate.

We see how different urban green infrastructure types, from urban forests to lawns, can act as carbon sinks. The three tested LSMs (JSBACH, LPJ-GUESS and SUEWS) effectively simulated seasonal and annual variations, as well as the impacts of weather events on carbon fluxes and related factors in both irrigated and non-irrigated lawns, park trees, and urban forests. Irrigation as key management practise emerged as a key factor often improving carbon sequestration. Tree-covered areas demonstrated greater carbon sequestration rates compared with lawns on an annual scale. Meadows are not better carbon sinks than lawns under typical summer conditions, but their drought resilience is better maintaining their capacity to uptake carbon also during drier periods contrary to lawns. In Helsinki, the city-level biogenic carbon sinks are expected to increase with climate change by 11% mainly due to the longer growing season whereas carbon sinks in forested areas decreased due to increased environmental stress. This research emphasizes the importance of integrating diverse vegetation types and impacts of irrigation into urban carbon modelling efforts to inform sustainable urban planning and climate change mitigation strategies.