Objective The construction of urban green infrastructure is one of the major scientific and technological tasks to cope with environmental risks such as global climate change and ecosystem imbalance. As a nature-based solution, urban green infrastructure (UGI) policy tools have become an important means led by the government to promote the construction of urban green infrastructure.
Methods With UGI policy tools as the research object and text retrieval, econometric analysis and coding classification as research clues, this research, by virtue of Bibliometrix R Package software and CiteSpace software, conducts a visual analysis of the research status, hot trends and research directions in the field of UGI policy tools. Specifically, the research deeply analyzes the development history of 12 typical UGI policy tools, compares the strengths and weaknesses of their derivative background, implementation purpose, indicator system, performance assessment method, and policy regulation path, and analyzes the ways and means for organically combining UGI construction and management with ecosystem service objectives, aiming to provide policy guidance and technical support for the optimization and improvement of UGI.
Results The core issues of green infrastructure evaluation tools include basic performance, benefit evaluation and index measurement methods. “Ecosystem services” and “green infrastructure assessment” are the driving themes, and evaluating green infrastructure in combination with ecosystem services has become an important trend. Based on the map of national scientific research output and the map of tool citations, 12 representative policy tools are selected. The development of such tools has gone through three stages: enlightenment, exploration and development. In the first stage, in response to the challenges of land management and stormwater environment issues caused by urbanization, Berlin and Malmo developed representative policy tools to creatively integrate landscape elements such as greening, water system and soil in urban planning and design, and effectively guide the quantity increase and quality optimization of urban landscape through evaluation indicators. In the second stage, different cities developed their distinctive solutions to urban rainwater, climate and environment problems. In the third stage of exploration, green infrastructure assessment tools mainly implemented in Stockholm in Sweden, Melbourne in Australia, etc., gradually focused on the assessment of ecosystem service performance.By combing and comparing 12 typical UGI policy tools, this research obtains the following findings. 1) UGI policy tools have gradually become a powerful means to deal with urban challenges, with their target orientation shifting from solving a single stormwater problem to assessing multiple benefits of ecosystem services. 2) The research unifies the indicator terms involved in UGI policy tools and encode and classify them with reference to the standard NbS terms and classification methods described in Nature4Cities (N4C) issued by the United Nations Environment Programme. Policy indicators range from the integration of greening, water system and soil elements to a hierarchical system that includes project elements such as surface cladding vegetation, surface blue and green facilities, vertical greening of buildings, and green roofs of buildings, as well as management elements of direct intervention and animal intervention. 3) The tools can be divided into the “conformative” mode of mandatory land use restriction or the “performative” mode of indirect encouragement, combining the two complementary urban development project screening mechanisms of standard weight and performance threshold, covering the whole process from planning, construction to control and monitoring. 4) It has become an urgent need to calibrate the performance of UGI policy tools according to ecosystem service demand, and to develop tools to assess the effectiveness of regulatory services (carbon sequestration and climate regulation), provision services and cultural services of UGI. Therefore, in the future, synergies and trade-offs between ecosystem services can be incorporated into the weighted basis, and a UGI policy tool covering a multi-objective evaluation system may be developed to examine the potential ecological, social and economic benefits of different green infrastructure solutions.
Conclusion The development of UGI policy tools will become a powerful weapon to deal with global issues and urban challenges. It is recommended to, in alignment with the interntional general classification standard for NbS, unify the UGI discourse system involving UGI type definition, dimension and scale to provide policy guidance and technical support for the optimization and improvement of UGI.
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