Research on Management Index System of Low-Carbon Community Open-space under Dual-Carbon Goal

: This paper selects the theory of "carbon source, carbon sink and carbon neutralization" witch has high applicability in the "dual-carbon" target theory, to clarify the construction of low-carbon community open space under the "dual-carbon" target. Discuss the realization of low-carbon community open space under this theory, and build the target layer and secondary indicator layer of low-carbon open space construction management indicators based on this theory. Fifty representative indicators related to the open space in low-carbon communities are selected from the eight widely used evaluation index systems in the world. According to the implementation path of the "double carbon" goal of the open space in low-carbon communities, these indicators are divided into six categories: "energy utilization", "resource utilization", "transportation", "carbon pool", "carbon absorption" and "low-carbon community management and culture”. Take the six categories as framework, combined with current condition and research status in China, the relevant indicators of "carbon absorption" are supplemented, and a low-carbon community open space management index system including three first-class indicators, six secondary indicators and twenty-eight tertiary indicators is constructed.


Introduction
Striving to "peak carbon" in 2030 and achieve "carbon neutrality" by 2060 is China's solemn commitment to the international community. In 2020, China's total carbon emissions reached 10.251 billion tons, accounting for about 25% of the world's total emissions, of which urban carbon emissions accounted for about 60%, according to the seventh population census data in 2021. China's urbanization rate is only 63.89%, while the average urbanization rate of developed countries worldwide is 81.30%. Urban sprawl and urban carbon emission reduction will coexist long [1]. As a collection of multiple urban elements, including buildings, green spaces, squares, and other urban elements [2], the community affects not only the emission of urban carbon but also the absorption of carbon dioxide. Therefore, China attaches great importance to the construction of low-carbon communities. Over 400 Low-carbon communities have been constructed in over 20 provinces [3]. The natural open space in the community, dominated by green space and water bodies, is the main carbon sink space of the community. Therefore, community open space plays a critical role in constructing low-carbon communities. Foreign low-carbon communities developed earlier and maturely, forming a series of mature and widely used lowcarbon community evaluation index systems [4]. However, evaluating "low carbon" in community-scale open spaces is not yet systematic. Therefore, the research on the community evaluation index system and the screening and analysis of the indicators on community open space play a critical role in constructing the low-carbon community open space management index system and construction strategy under the dual carbon goal.

Objectives and approaches for the construction of open spaces in lowcarbon communities under the dual carbon goals
"Double carbon" means carbon peak and carbon neutrality, and global scholars have carried out extensive research on this goal, mainly in three categories: 1) From the perspective of technology and system, Unruh proposed the theory of "carbon lock" and "carbon unlocks" [5,6]. "Carbon lock" means that the world's industrial economy currently links to the use of fossil energy in terms of technology and system. The pursuit of rapid economic development will inevitably bring high carbon emissions. Reducing carbon emissions means economic development is stagnant due to the "technology-system locking" effect. On the contrary, there are three ways to "carbon unlock": (1) Do not change the existing technical system and system and control the terminal exhaust emissions, (2) maintain the overall framework of existing technical systems and systems, optimize some of their processes or adopt new technologies; (3) Completely abandon existing technical systems and systems, and adopt new low-carbon technologies to build low-emission technology systems and systems; 2) Some scholars have put forward the theory of "carbon emission decoupling" from the perspective of economics, that is, economic growth is separated from material consumption [7]. It can be divided into "relative decoupling" and "absolute decoupling." "Relative decoupling" means that under the premise of ensuring economic growth, pollution, waste, and resource consumption growth rate is lower than the economic growth rate. "Absolute decoupling" refers to reducing pollution, waste, and resource consumption under the premise of economic growth [8]. "Decoupling" can be further divided into "strong decoupling," "weak decoupling," "invisible decoupling," and "negative decoupling" [9]. 3) The most widely used and recognized is the "carbon source, carbon sink, and carbon neutrality theory, " proposed from the perspective of the natural carbon cycle. Carbon source refers to the source of greenhouse gases such as carbon dioxide produced by nature and human activities. Carbon sink refers to the absorption and storage of carbon dioxide by nature. Carbon neutrality refers to anthropogenic emissions of carbon dioxide (fossil fuel use and soil use) absorbed by human efforts (wood stocks, soil organic carbon, engineering storage, Etc.) and natural processes. Natural carbon sources mainly include soil and water, but soil and water are also essential carbon reservoirs. The assessment of CO2 emissions from human activities usually uses a full life cycle assessment. From the whole life cycle perspective, the assessment includes raw material mining, production and processing, transportation, product manufacturing, and production, use, and maintenance, dismantling, and recycling. From this point of view, the use of primary and secondary energy in human activities, the use of materials and products, and the treatment of waste (solid, water, gas) can all regard as carbon sources. Carbon sinks use natural vegetation, soil, water bodies, and engineering measures to absorb and store carbon dioxide.
Low-carbon community is a human production and living area built to reduce greenhouse gas emissions and energy consumption and increase carbon sinks, including community buildings, outdoor community environment, and residents living and production behaviors. According to the construction content, including community buildings, community transportation systems, community energy systems, community greening systems, community waste recycling systems, community management systems, and community low-carbon culture, Open space refers to the public external space in the city, including natural scenery, squares, roads, public green spaces, and recreational spaces. The definition of open space varies slightly from study to study, but these definitions all include the openness, publicity, and leisure of open space. Low-carbon community open space is a low-carbon community's open, public, and leisure part. Its main body comprises the community greening system, the central community transportation system, the community waste recycling system, and some community buildings and energy systems. Based on the current research results, the specific construction elements of low-carbon community open space can be summarized: (1) Low-carbon community layout and construction standards: relevant standards for low-carbon community construction, such as energy consumption standards, building materials standards, Etc., as well as overall planning including buildings making full use of renewable energy such as solar, wind, and geothermal energy or using local topography and climate to reduce energy consumption. (2) Green building roof and wall: use the building roof and wall space to grow plants; (3) Low-carbon outdoor infrastructure: low-carbon community open spaces include infrastructure such as lighting, traffic signals, and irrigation; (4) Low-carbon community transportation system: a road network or facility built to guide residents to adopt low-carbon transportation modes (walking, bicycle, public transportation, and new energy vehicles); (5) Low-carbon community carbon sink: low-carbon community vegetation, water construction, and biodiversity conservation; (6) Low-carbon community resource utilization and recycling: low-carbon community materials, water and waste utilization, and recycling; (7) Low-carbon community management and culture: lowcarbon community open space management measures, programs and cultural construction to guide low-carbon life.
This paper uses the "carbon source, carbon sink, and carbon neutrality" theory to construct the relationship between macro-scale dual carbon goals and communityscale construction elements. The macro goals are to reduce greenhouse gas emissions (carbon sources) and increase carbon dioxide absorption and storage (carbon sinks). "Carbon sources" include energy consumption, water consumption, material use, and waste disposal. In the open space of low-carbon communities, energy consumption mainly includes the electric energy consumption of various facilities and the fossil energy consumption of transportation. In order to facilitate research, energy consumption is decomposed into energy consumption based on electricity consumption and transportation consumption based on fossil energy. Water consumption, material use, and waste disposal are classified as resource utilization. Therefore, the implementation of carbon source targets in low-carbon community open spaces can be divided into three aspects: energy utilization, resource utilization, and transportation. The carbon sink goal is mainly to increase carbon dioxide absorption and increase carbon dioxide storage. Low-carbon communities generally do not have carbon dioxide engineering storage conditions, mainly natural systems, vegetation, soil, and water absorption and storage, which can be divided into carbon pool and carbon absorption two aspects. In addition, low-carbon awareness, low-carbon education, and low-carbon management of community residents are some essential goals of low-carbon community open space, which can be achieved by low-carbon community management and cultural approaches. The details are shown in Table 1. The way to achieve the "dual carbon" goal of lowcarbon community open space is related to the construction factors. Raising community energy consumption standards and using community spatial layout to improve the thermal environment of buildings is related to the elements of "low-carbon community layout and construction standards" and "low-carbon outdoor infrastructure." Renewable energy utilization targets can be achieved through solar energy, wind energy utilization, Etc., and solar energy and other utilization devices in the community are generally on the roof or wall, related to the "green building roof and wall." "Resource utilization" involves using water resources, building materials, and waste. Water resources involve community water conservation standards, while building materials and waste involve community resource utilization and recycling. Therefore, it is related to "low-carbon community layout and construction standards" and "lowcarbon community resource utilization and recycling" among the construction elements. The "transport" aspect relates to the carbon of "low-carbon community transportation." "Carbon sequestration" and "carbon pool" are both related to "low-carbon community carbon sinks." Low-carbon community management and culture are the elements of low-carbon community open space construction, and it is also the way to achieve the dual carbon goal. The correlation between the realization of the dual carbon goal and the elements of low-carbon community open space construction is shown in Figure 1.

A complete theoretical system and management indicators for constructing low-carbon community open-spaces in
China have yet to be completed. By analyzing the lowcarbon community evaluation index system widely used at home and abroad, this paper analyzes the indicators related to the open space of low-carbon communities, screens the indicators, and constructs the low-carbon community open-space construction management index system according to the actual situation in China.

Evaluation indicators of low-carbon communities at home and abroad
The development of the foreign community evaluation index system is relatively mature, generally developed from the green building evaluation index system. The indicators of each division of the same system have the characteristics of unity and relevance, so it has been widely used.

Analysis of indicators related to open space in low-carbon communities
In order to screen out the indicators related to the open space of low-carbon communities in the index system, the indicators in the selected index system are divided into two categories: related to and not related to the open space of low-carbon communities, and the results are as follows: The number of indicators of the six low-carbon community evaluation index systems, such as BREEAM, LEED-ND, CASBEE, DGNB, GM, and the Guide, is between 36~52, and the number of indicators related to open space in low-carbon communities accounts for more than 50%. Compared with other low-carbon community evaluation indicators, Singapore's GM community evaluation index system pays more attention to community open space construction, accounting for 80.56%, and the others are 51.22%~65.12%. SITES was specially developed for the built environment outside the site building, and the proportion of "relevant" indicators is as high as 85.07%. However, China's ASGB index system is a green building evaluation index, and the number of internal evaluation indicators of buildings is large. The number of "related" indicators accounts for only 39.18%.
The indicators related to the open-spaces of lowcarbon communities are further classified according to construction elements. In general, low-carbon community resource utilization and recycling and low-carbon community transportation system are the two points to which all index systems pay the most attention, accounting for 32% and 23% of the indicators, respectively. The carbon sink index of low-carbon communities accounts for about 13%, of which more than 60% is distributed in SITES and CASBEE and less in other index systems. Low-carbon community layout and construction standards account for about 12%, mainly concentrated in ASGB standards. Green building roofs and walls, low-carbon outdoor infrastructure, and low-carbon community management and culture accounted for 3%, 7%, and 10%, respectively.
After screening the indicators related to low-carbon community open space in each index system, 50 indicators were summarized according to the construction path of low-carbon community open space under the theory of "carbon source, carbon sink, and carbon neutrality" and classified by "energy utilization," "resource utilization," "transportation," "carbon pool," "carbon absorption" and "low-carbon community management and culture."

Selection of low-carbon community open space management indicators and target setting
According to the theory of "carbon source, carbon sink, and carbon neutralization," "Carbon source," "carbon sink," and "low-carbon community lifestyle construction" as the target indicators (primary indicators). "Energy utilization," "resource utilization," "transportation," "carbon pool," "carbon absorption," and "low-carbon community management and culture" are secondary indicators. The third-level indicator is the management indicator for constructing low-carbon community open space under the theory of "carbon source, carbon sink, and carbon neutrality." There is a phenomenon of homogeneity in urban development, and urban communities in various countries are also homogeneous to a certain extent. Therefore, the index values in this paper refer to the recommended values given by similar indicators in the "Guidelines for the Pilot Construction of Low-carbon Communities" and "Green Building Evaluation Standards" if there are no similar indicators, they are selected from other index systems. If there are no similar indicators in each index system, the recommended values are given by reference research and practice. This paper sets the reference value of the lowcarbon community open space management index system about the similar index values in these index systems. The specific reference values and interpretations are shown in Table 4.
The existing indicators are related to the carbon pool. However, the indicators are not pertinent, so the carbon pool and absorption indicators are selected based on the current research results.
Carbon absorption is directly related to the carbon pool, which also means increasing the carbon pool. However, for soil and water bodies, the stability of preserving their stock carbon is more critical due to the simultaneous process of carbon sequestration and carbon decomposition within them. The carbon pool index is mainly used to maintain the stability of carbon in soil and water stocks. The carbon absorption index focuses on increasing the ability of vegetation to absorb carbon dioxide per unit of time. According to relevant studies, soil organic carbon storage in green garden space directly impacts upper soil vegetation and vegetation maintenance. Good vegetation cover can increase soil organic carbon content [10,11,12]. Therefore, the "soil vegetation cover" is set to 100%. The carbon content of the soil under paving is related to whether the paving is permeable. The carbon content of the soil under permeable paving is higher than that under impervious paving. According to practical experience, the "permeable paving rate" is 80%. Water carbon reservoirs in low-carbon community open spaces are related to water pollution, and reducing non-point source pollution is conducive to the stability of water carbon pools [13,14,15]. According to practical experience, "water quality in the community reaches Class III. and above," and "ecological barge rate" is not less than 80% as indicators and reference values.
In terms of "carbon sequestration," there is a lack of indicators to measure the ability of vegetation to absorb carbon dioxide. Studies have shown that different plants have different abilities to absorb carbon dioxide, and applying tree species with solid carbon dioxide absorption capacity in stable plant species can significantly increase the carbon sequestration capacity of vegetation communities. Considerable research on the configuration of high carbon sequestration tree species and high carbon sequestration plants in different regions, and the combination of deciduous trees and evergreen shrubs, evergreen and deciduous trees, and slow growth and fast growth can effectively increase the carbon sequestration capacity of vegetation communities. Some scholars have studied the impact of the overall configuration of plant communities on the carbon sequestration capacity of plant communities. The carbon sequestration capacity of green space has increased by 20%~30% compared with before optimization [16]. So the indicator of "increase rate of carbon sequestration per unit of green space compared with the regional average" is not less than 20%, and the "proportion of local high-carbon sequestration plant community area" is not less than 40% regarding the SITES index system.
The construction of a low-carbon community lifestyle needs to be realized through community low-carbon management norms and low-carbon awareness cultivation. Low-carbon community management can be achieved through carbon emission monitoring schemes. The carbon emissions of all aspects of low-carbon community open space through the monitoring plan are released to urge residents and community managers, so the "Community carbon emission monitoring plan" is included in the index. Regarding the international mature index system, cultivating low-carbon awareness is equally important. Low-carbon lifestyle guides, knowledge and popular science, and other community low-carbon life publicity and education are needed. Therefore, the "community low-carbon life publicity and education program" will be included in the index.

Conclusion
Based on the "carbon source, carbon sink, and carbon neutrality" theory, this paper constructs a low-carbon community open space management index system with three first-level, six second-level, and 29 third-level indicators. The low-carbon community open space management index system is constructed as follows: In order to make the management index system better guide the construction and management of open space in low-carbon communities, the following points should be emphasized: (1) The index system of low-carbon community open space management guides planning and design. The management index system is used to guide the planning and design. Furthermore, the pre-assessment of the open space of low-carbon communities is carried out according to the design objectives at the design stage, and the "carbon source" and "carbon sink" of the open space of low-carbon communities are considered as a whole. Improve the scientific and quantifiable construction of open space in low-carbon communities.
(2) The low-carbon community open space management index system standardizes the management and operation. After the low-carbon community open space completes the management index assessment, the various plans in the indicator are implemented. In particular, the "Community Carbon Emission Monitoring Program," long-term monitoring of carbon emissions in low-carbon community open space, is conducive to further improving the index system, guiding the construction of low-carbon community open space, and timely discovering various problems in the operation process.
(3) Pay attention to the update and development of the community open space management index system. With the development of science and technology and the times, the only timely update is the management index system and the development of community open space construction matching; there is no lag and disconnection, and the update of the index system includes the update of specific indicators and reference values.
(4) Focus on "low-carbon lifestyle construction." The construction of low-carbon community open space focuses on guiding residents' lifestyles to shift to lowcarbon. Although it accounts for a small proportion of the management index system, it is the fundamental guarantee and goal of constructing open space in low-carbon communities.