Nature-based solutions are some of the most effective strategies to promote sustainable city development; however, existing research on NbS is mostly comprised of single variable studies rather than multiple variables. The purpose of this study was to explore the possibility of extending the NbS of a single variable to two variables for the better development of sustainable cities. Both forestation and wetland restoration are regarded as NbS for sustainable city development. The research approach of “forest–wetland” NbS was proposed and centers on the process and core issues of traditional NbS. Taking Tianjin as an example, the spatial patterns of forests and wetlands, correlation between the spatial distribution of forests and wetlands, and spatial correlation between the areas of forest growth and wetland growth within a certain distance in different years were studied using a spatial distribution pattern analysis, geographic concentration analysis, kernel density estimation and spatial autocorrelation analysis. Based on the core issues of NbS and the above spatial analysis, a “forest–wetland” spatial planning strategy was formulated. The main conclusions are as follows: forest and wetland were negatively correlated in the whole area of Tianjin, forest resources w mainly located in north, while wetland resources were mainly located in south. Compared with forests, the spatial distribution of wetlands in Tianjin was more balanced. There exist synergy and trade-offs between forest and wetland area under certain circumstances. Growth of forests was positively correlated with the growth of wetlands, within a distance of 0–400 m from 2000 to 2010, and within a distance of 0–600 m from 2010 to 2020. An increase in forest area will lead to an increase in evaporation, which in turn will hinder the growth of wetlands in Tianjin. Forest–wetland ecological network could promote synergistic between forest and wetland, and grey infrastructure to reduce potential trade-off between forest and wetland.

The water ecosystem, an essential component of the United Nations Sustainable Development Goals, faces challenges such as water scarcity. Resilience is one of the central objectives of sustainable development. This study aims to investigate the water ecosystem resilience in Tianjin, providing a reference for protecting and restoring the global water ecosystem. Using the DPSIR model, an evaluation system for water ecosystem resilience was constructed. The combination weighting method was used to determine the weights of evaluation indicators. A case study on the water ecosystem resilience of Tianjin reveals spatial differences in 2018, with higher resilience in the north, and lower in the south. From a spatial planning perspective, forest coverage and wetland rate are representative evaluation indicators that significantly impact Tianjin's water ecosystem resilience. The overall connectivity index analysis method was used to analyze the representative evaluation indicators, and enhancement strategies such as building forest cities and protecting and restoring wetland systems were proposed. This study provides theoretical support for improving the water ecosystem and technical guarantees for achieving sustainable development.