Multi-Objective Urban Green Space Optimization of Wetland Cities Based on the Carbon Balance: A Case Study in Wuhan

Urban areas are significant centers of human activity and are recognized as major contributors to global carbon emissions. The establishment of urban green spaces plays a crucial role in enhancing carbon sinks and mitigating carbon emissions, thereby fostering a low-carbon cycle within cities. However, the existing literature on the carbon sequestration of green spaces in Chinese cities often overlooks the role of water bodies, which are a significant characteristic of wetland cities. Therefore, it is necessary to investigate the carbon sequestration potential of green spaces in wetland cities, taking into account the contribution of water bodies to carbon sinks. This study aims to analyze the quantitative structure of urban green spaces through the lens of carbon balance, which can effectively enhance a city’s overall carbon sequestration capacity. Utilizing carbon balance theory, this research first assesses the carbon offsetting capability (COC) of urban green spaces in Wuhan for the year 2019. It then forecasts future carbon emissions, sets improvement targets for COC, and calculates the required area of standard green space to achieve these targets by 2030. A multi-objective programming (MOP) model is developed to identify the optimal solution that aligns with urban development planning constraints while maximizing carbon sinks. Lastly, we analyzed the contribution rates of different types of urban green spaces to the total carbon sequestration capacity of green spaces to clarify the characteristics of carbon absorption in green spaces of Wuhan, a wetland city. The findings indicate the following: (1) In 2019, Wuhan’s carbon emissions from human activities reached approximately 38.20 Mt, with urban green spaces absorbing around 5.62 Mt of carbon, and a COC of about 14.71%. (2) Projections for 2030 suggest that carbon emissions in Wuhan will rise to approximately 42.64 Mt. Depending on the targeted COC improvement rates of 5%, 10%, 15%, 20%, and 25%, the required values of carbon sequestration will be 6.59 Mt, 6.90 Mt, 7.21 Mt, 7.53 Mt and 7.84 Mt, respectively. (3) The results of the MOP model indicate that the optimal COC for 2030 is projected to be 16.33%, which necessitates a carbon sequestration of 6.97 Mt. (4) Water bodies accounted for 56.23% of the total carbon absorption in green spaces in 2019 and are projected to represent 45.37% in 2030, highlighting the distinctive characteristics of Wuhan as a wetland city in terms of its green space carbon sequestrations. The management and enhancement of water body carbon sequestration capacity is crucial for the carbon sequestration potential of urban green space in Wuhan. The results of this study can provide evidence and recommendations for the low-carbon development patterns of wetland cities across China.