- Email: [email protected]
Carbon Reduction Effects of Sponge City Construction: A Case Study of the City of Xiamen
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Energy Procedia 152 Energy Procedia 00(2018) (2017)1145–1151 000–000 www.elsevier.com/locate/procedia
Applied Energy Symposium and Forum 2018: Low carbon cities and urban energy systems, CUE2018-Applied Energy andLow Forum 2018: Low carbon andsystems, Applied Energy Symposium andSymposium Forum 2018: carbon cities and urbancities energy CUE2018, 5–7 June 2018, Shanghai, China urban energy systems, 5–7 June Shanghai, CUE2018, 5–7 June 2018,2018, Shanghai, ChinaChina
Carbon Reduction EffectsSymposium of Sponge City Heating Construction: A Case The 15th International on District and CoolingA Case Carbon Reduction Effects of Sponge City Construction: Study of the City of Xiamen Study of the Xiamen Assessing the feasibility of City usingofthe heat demand-outdoor
Weiwei Shaoaa, Jiahong Liua,b, *, Zhiyong Yangaa, Zhaohui Yangaa, Yingdong Yuaa, Weijia temperature function a long-term districtYang heat demandYuforecast Weiwei Shao , Jiahong Liua,b,for *, Zhiyong Yang , Yingdong , Weijia Liaa* , Zhaohui Li * a c State Key Laboratorya,b,c of Simulation and Regulation of WateraCycle in River Basin,b., China of WatercResources Hydropower I. Andrić *, A. Pina , P. Ferrão , J. Fournier B. Institute Lacarrière , O. Leand Corre State Key Laboratory of Simulation and RegulationResources, of Water Cycle in100038, River Basin, Beijing ChinaChina Institute of Water Resources and Hydropower a a
a
b Resources, 100038, China of Transportation andand Civil Engineering Foshan University, Guangdong China IN+ CenterSchool for Innovation, Technology Policy Research&Beijing - Architecture, Instituto Superior Técnico, Av. Rovisco Pais 1,528000, 1049-001 Lisbon, Portugal b b School of Transportation and Civil & Architecture, Foshan University, 528000, China Veolia Recherche & Engineering Innovation, 291 Avenue Dreyfous Daniel, 78520 Guangdong Limay, France c
Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
Abstract Abstract Abstract This studyheating analyzed the effects the construction of sponge in China, recent years,effective on carbon emissionfor reduction based District networks are of commonly addressed in the cities literature as oneinof the most solutions decreasing the This study analyzed the reduction effects thebuilding construction of These sponge cities inrequire in recent years, on carbon based on the global emission targets and sector. China’s responsibility inChina, reducing carbon emissions. Sponge citiesreduction are built with greenhouse gas emissions fromofthe systems high investments which areemission returned through the heat onsales. the global reduction targets and China’s responsibility in reducing carbon cities could are built with rainwater infiltration, retention, storage, purification, reuse, and drainage facilities to emissions. promote natural Due toemission the changed climate conditions and building renovation policies, heat demand natural inSponge the accumulation, future decrease, rainwater infiltration, retention, purification, reuse,spaces. and drainage facilitiessponge to promote natural accumulation, natural infiltration, and purification of precipitation in urban In the process, city construction, by intensifying the prolonging the natural investment returnstorage, period. infiltration, and natural ofthe precipitation inarea urban spaces. the process, sponge city construction, by intensifying the treatment urban increases urban green expands the urban water surface. The increase in urban greening, The mainofscope ofsewage, thispurification paper is to assess the feasibility of and using the In heat demand – outdoor temperature function for heat demand treatment sewage, increases theand urban and expands urban Thereduction increase in consisted urbaningreening, expansion ofurban wetlands in urban rivers lakes, andarea use of rainwater resources tostudy. carbon theofcity. forecast. of The district of Alvalade, located ingreen Lisbon (Portugal), wasthe used as water a lead casesurface. district effects is 665 expansion wetlands in urban andperiod lakes, andtypology. use ofthe rainwater resources to(low, carbon reduction effects in Xiamen, thedistrict city. Considering the city of asrivers an example andand combining main measures forlead the construction of a sponge city three buildings of that vary inXiamen both construction Three weather scenarios medium, high) and Considering the city of were Xiamen as an example andintermediate, combining thedeep). main measures forthe the construction aheat sponge citythe in Xiamen, our quantitative analysis suggested that urban greening can reduce carbon emissions by error, 66,266.7 tonsofper year, and lake and renovation scenarios developed (shallow, To estimate obtained demand values were our quantitative analysis suggested that urban greening canper reduce 66,266.7 per year, and and river wetlands reduce carbon emissions 962.8 model, tons year. carbon The developed useemissions of rainwater resources in sponge citythe canlake reduce compared withcan results from a dynamic heatby demand previously andbyvalidated bytons thethis authors. river canby reduce carbon emissions bychange 962.8 per year. The use of rainwater resources in of thisChina's sponge city can reduce carbon emissions 2719.1 tonsonly per year. This showstons emission reductions from the could construction sponge cities are The wetlands results showed that when weather isthat considered, the margin of error be acceptable for some applications carbon emissions by 2719.1 tons perlower year.than This shows reductions from the construction China's sponge renovation cities are significant, resulting indemand effective responses to and mitigation of climate change.considered). (the error in annual was 20% forthat all emission weather scenarios However, of after introducing significant, effective responses and mitigation of on climate change.and renovation scenarios combination considered). scenarios, resulting the error in value increased up toto59.5% (depending the weather Copyright 2018 Elsevier Ltd. All rights reserved. The value©of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the Copyright © © 2018 Elsevier Elsevier Ltd. Ltd. All All rights rights reserved. reserved. Copyright Selection peer-review responsibility of the scientific committee Applied Energy Symposium and Forum 2018: Low decrease and in 2018 the number ofunder heating hours of 22-139h the heating of season on the combination of weather and Selection and peer-review under responsibility of the during scientific committee of the(depending CUE2018-Applied Energy Symposium and Selection andscenarios peer-review under responsibility of hand, the scientific committee of Appliedfor Energy Symposium and Forum 2018: on Low carbon cities and urban energy systems, CUE2018. renovation considered). On the other function intercept increased 7.8-12.7% per decade (depending the Forum 2018: Low carbon cities and urban energy systems. carbon cities and urban energy systems, CUE2018. coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and Keywords: City; Urban Green Land;estimations. Wetlands; Stormwater Management; Carbon Reduction Effect improve Sponge the accuracy of heat demand Keywords: Sponge City; Urban Green Land; Wetlands; Stormwater Management; Carbon Reduction Effect
© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +86-10-68781936; fax: +86-10-68483367 Cooling.
* Corresponding Tel.: +86-10-68781936; fax: +86-10-68483367 E-mail address:author. [email protected] E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the Applied Energy Symposium and Forum 2018: Low carbon cities Selection and peer-review under responsibility the scientific Selection peer-review responsibility of the scientific committee of the Applied Energy Symposium and Forum 2018: Low carbon cities and urbanand energy systems, under CUE2018. and urban energy systems, CUE2018. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the CUE2018-Applied Energy Symposium and Forum 2018: Low carbon cities and urban energy systems. 10.1016/j.egypro.2018.09.145
Weiwei Shao et al. / Energy Procedia 152 (2018) 1145–1151 Weiwei Shao et al./ Energy Procedia 00 (2018) 000–000
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1. Introduction From a global perspective, the rapid economic development, urbanization, and industrialization of any country is based on the massive consumption of energy. However, unlike in the past, the current problems are not restricted to rapid economic development; environmental problems, such as climate change, are serious global concerns. Because of global warming, extreme weather, such as high temperatures, droughts, and heavy rains, has occurred in many cities. The frequency and intensity of such extreme weather has increased significantly. These changes have made it difficult to sustain resource-consumption-style development, which leads to environmental harm. If we cannot effectively control greenhouse gas emissions, the global warming trend will continue, and humanity will be exposed to unpredictable risks. Therefore, effective actions should be taken to balance economic development with environmental protection. China is a major greenhouse gas emitter in the world. The pressure to reduce carbon emissions worldwide is severe. China’s share of global carbon emissions has increased from 20.9% in 2005 to 27.5% in 2014 [1]. Although the growth rate of carbon emissions has slowed in the past two years owing to low energy consumption, changing the global trend in carbon emissions will be difficult. As a responsible, developing country, China has been actively responding to climate change (Table 1). The 2014 China-U.S. Joint Statement on Climate Change included a clear plan for achieving a peak in CO2 emissions by approximately 2030 [2]. With this agreement, the goal is to reach an early peak in CO2 emissions with plans to increase the share of non-fossil energy sources in primary energy consumption to approximately 20% by 2030. In 2016, China politically supported the signing of the Paris Agreement, which opened a new phase of global cooperation to address climate change. When developing its Thirteenth Five-Year Plan, China adhered to concepts regarding innovation, coordination, green initiatives, openness, and shared development. The plan vigorously promotes low-carbon development and effective actions to address climate change. Table 1. China's responses to global warming Year
Response
2005
CO2 emission reduction targets were proposed in the National Eleventh Five-Year Plan.
2007
The National Plan for Addressing Climate Change was announced.
2009
The National People's Congress passed the Resolution on Actively Addressing Climate Change.
2009
The State Council proposed that the carbon intensity in 2020 be 40%–45% lower than the carbon intensity in 2005.
2012
A greenhouse gas control program was introduced that required a 17% lower carbon intensity in 2015 than in 2010.
2014
The China-U.S. Joint Statement on Climate Change was released in which a 2030 emission peak and non-fossil fuel energy targets were proposed.
2015
China submitted the National Indigenous Emissions Reduction Contribution plan, which proposed to lower carbon intensity by 60% in 2030, based on levels of 2005.
2016
The Paris Agreement was signed and ratified by the Standing Committee of China’s National People’s Congress in September, and China became the 23rd Party to complete the ratification agreement.
China is developing “sponge cities” as a new urban construction mode. A sponge city is a city that acts like a sponge to absorb storm water runoff from impervious surfaces and has good elasticity with regards to adapting to environmental changes and responding to natural disasters. When it rains, a sponge city absorbs, stores, and purifies the water. When required, the stored water is released and added to the urban water supply. Since the launch of China's national strategy for sponge cities in late 2013, the construction of sponge cities has become an important factor in environment friendly construction and economic development. Based on the first group of 16 pilot cities in 2015 and the second group of 14 pilot cities in 2016, provinces have issued guidance on promoting the construction of sponge cities. Cities around China have also developed plans for sponge cities. A sponge city accumulates rainfall in original landforms and uses the ecological background of rainwater and the natural underlying surface of the land, allowing the water to be naturally purified by vegetation, soil, and wetlands. Sponge cities can be flexible, adapt to changes in the environment, and respond to natural disasters. The construction of sponge cities in urban
Weiwei Shao et al. / Energy Procedia 152 (2018) 1145–1151 Weiwei Shao et al. / Energy Procedia 00 (2018) 000–000
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development and construction will strengthen planning in, improve management of, and increase control over urban construction; will lead to the adoption of measures such as source abatement, process control, and system governance to cope with the urban non-point source pollution; and involve the use of techniques such as roof greening, permeable paving, swales, rainwater storage ponds, and river and lake wetlands. Sponge cities are constructed to address drought, erosion, water pollution, and the urban heat island effect. The relationship between China's sponge cities and low-carbon development has not been thoroughly explored. The carbon emissions from the construction of sponge cities and the question of whether sponge cities contribute to the reduction of urban emissions require further study. Therefore, an analysis of carbon reductions from the construction of sponge cities can provide in-depth information, which may promote construction of sponge cities to improve a city’s ability to adapt to climate change in China. 2. Overview of carbon reductions from sponge city construction Currently, more than 50% of the world's population is concentrated in cities, with these city dwellers consuming approximately 75% of the world’s energy and producing 80% of its greenhouse gas emissions [3]. Carbon emission sources for cities include the burning of fossil fuels, the oxidation and corrosion of organic materials, and human and biological resources (respiration, tree felling, etc.). Many cities now have their own low-carbon development indicator systems in place to limit carbon emissions in fields such as industry, construction, and transportation. However, the planning and construction of low-carbon cities cannot rely solely on reducing carbon emission sources; an increase in carbon sinks in cities is also needed. Sponge cities, through the combinations of artificial and natural infrastructure, ecological and engineering measures, and surface water and groundwater, can help resolve problems of carbon emissions in urban areas, address malodorous black and odor issues in water, and improve water ecology. At the same time, sponge cities can form urban carbon sinks, regulate the microclimate, and ease the heat island effect. Therefore, the construction of sponge cities can transform urban development concepts and construction methods. Carbon emission reduction in sponge city construction is mainly achieved through processes such as, direct carbon fixation in urban green systems, fossil fuel energy and emission reductions and carbon reduction on hardened ground. 2.1. Direct carbon fixation in urban green systems Urban green systems are the most important carbon sinks in cities. The scattered plants in urban areas that fix CO2 from the air in the plants or soil via photosynthesis form the carbon sinks in urban green systems. Sponge city construction will increase the urban afforested area and the growth of grassland biomass through green roofs, rainwater gardens, sunken green spaces, planted trenches, wetlands, and other green systems. This will increase the absorption of carbon. The enhanced role of carbon sinks will result in direct emission reductions. This can effectively curb and mitigate the urban heat island effect and global climate change, to a certain extent, and at the same time, beautify and improve the living environment, and provide ecological, social, economic, and cultural benefits. 2.2. Fossil fuel energy and emission reduction A sponge city construction includes green roofs, rainwater storage tanks, river and lake wetlands, and grassed swales, as well as ecological reconstruction of roads and communities. Through the construction of sponge cities, the urban heat island effect will be greatly reduced, the community’s ecological environment will be optimized, residents’ use of air conditioners and other electrical appliances will be reduced, and residential and commercial power consumption will decrease. According to relevant results, the community’s energy consumption will be directly reduced by more than 30% [4].
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2.3. Carbon reduction via permeable pavement In the construction of sponge cities, the large amount of impervious surface needs to be reduced through the construction of pervious paving or green spaces. Thus, the amount of cement used will be reduced. The carbon footprint in cement production is high and includes raw material production, raw material transportation, and cement production and processing. The carbon emissions from cement production and processing are mainly from fuel combustion, chemical reactions, and electricity consumption in production. For all types of cement, the carbon emissions from the decomposition of carbonate minerals account for the largest proportion of the total carbon emissions (ranging from 47–56%). According to relevant research results, approximately 100 tons of limestone produced from the decomposition of 100 tons of raw materials for cement will produce approximately 44 tons of CO2 [5]. 2.4. Reduced consumption and emission reduction in sewage treatment Low concentration and low loads will affect the effective operation of the sewage treatment plant, cause unnecessary energy consumption, and reduce efficiency of the sewage treatment system [6]. In their construction, sponge cities can increase the efficiency of waste water facilities through the improvement of the drainage network, increase in the sewage collection rate, optimization of collection systems for sewage treatment facilities (such as the addition of adjustment pools), enhancement of water-saving management, and improvement of the water use efficiency. The amount of clean water ensures that the sewage treatment facilities are operating under optimal design conditions, which improves the efficiency of pollutant emission reduction. 2.5. Carbon reduction through rainwater use Sponge city construction will increase the use of rainwater resources and reduce the consumption of tap water, which will reduce carbon emissions from the production and supply of tap water. Therefore, sponge city construction can change the carbon footprint of the original urban construction methods, and this carbon reduction can be significant. From the above analysis, we can see that through protection and restoration of the ecological environment, the construction of sponge cities can contribute to reduced carbon emissions and consumption. 3. Study area Located in the southeastern part of Fujian Province, China, the city of Xiamen has a land area of 1,699 km2. The average annual precipitation is 1,530 mm, decreasing from northwest to southeast. Xiamen was in the first batch of pilot cities for sponge city construction approved by the state in 2015. Sponge city construction in Xiamen included six aspects: pollution prevention and control, construction of ecological water systems, construction of drainage and flood control systems, construction of garden spaces, construction of roads, and construction of sponge residential communities. Measures and indicators of sponge city construction in Xiamen were divided into 16 units. Through the construction of various management and control units, the construction goals of the entire sponge city were achieved, including control of 70% of the total annual runoff, making the city more green, natural, and flexible. 4. Methods and results
4.1. Estimating the urban carbon reduction effect In 2014, Xiamen had 11,172 ha of green space. According to the construction plan of the sponge city, Xiamen plans to establish 18647.79 ha of green land by 2020, including 5161.09 ha of city parks, 1373.33 ha of regional parks, 1246.41 ha of special parks, 2831.71 ha of linear parks, 508.85 ha of community parks, 1971.15 ha of greenery along streets, and 5543.25 ha of protection zone green space. According to a relevant scholar’s calculations
Weiwei Shao et al. / Energy Procedia 152 (2018) 1145–1151 Weiwei Shao et al. / Energy Procedia 00 (2018) 000–000
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[5], green coverage is closely related to the CO2 concentration in the air, and 100 m2 of urban green space can absorb approximately 325 kg CO2 per day. According to this method, we roughly estimated that through the construction of planned green land in the sponge city, the city of Xiamen would achieve a carbon reduction of 66266.70 tons per year.
4.2. Estimation of the carbon reduction from river and lake wetlands Owing to their structural composition, wetland ecosystems play an important role in absorbing atmospheric greenhouse gases and slowing down global warming. The wetland carbon sink formula is [7][8]: (1) where Cs is the amount of carbon fixed in the wetland per year, Si is the area of the wetland (m2), and Pi is the rate of carbon sequestration in the wetland per unit area (g-C m-2 a-1). Some scholars have consolidated sedimentary data from lake and marsh wetlands in China over the past 100 years by consulting wetland surveys and the literature. Table 2 shows the estimated carbon fixation rates for wetlands across China that have been calculated based on their sedimentation rates and sediment composition. Table 2. Rates of carbon sequestration for lake wetlands in China Location
Carbon fixation rate, Pi (g-C m-2 a-1)
Eastern Plain Lake Wetlands
56.67
Mengxin Plateau Lake Wetlands
30.26
Yunnan-Guizhou Plateau Lake Wetlands
20.08
Qinghai-Tibet Plateau Lake Wetlands
12.57
Northeast Plains and Mountain Lake Wetlands
4.49
Through the construction of a sponge city in the city of Xiamen, the areal proportion of Xiamen's rivers, lakes, and wetlands will increase from 6% in 2014 to 7% by 2020, with an increase in area of approximately 16.99 km2 (using the carbon sequestration rate of lake wetlands in the eastern plains). It is estimated that 962.8 tons per year of carbon reduction will be achieved through the construction of river and lake wetlands.
4.3. Estimation of the carbon reduction from the use of rainwater resources Sponge city construction will increase the use of rainwater resources and reduce the consumption of tap water. According to scholars' analyses, producing 1 m3 of tap water requires approximately 0.194 kg of carbon [5][9]. According to the plans for construction of the sponge city in Xiamen, the utilization rate of rainwater resources will increase from 0.5% (approximately 3.163 million m3) of the total water use in 2014 to 2% (17.18 million m3) of the total water consumption by 2020, leading to savings in tap water usage. The use of approximately 14.016 million m3 of rainwater will reduce carbon emissions by approximately 2719.1 tons per year. 5. Discussion Owing to imperfect data, empirical methods were used in this study for the calculations and analysis. In the future, it will be necessary to refine the analysis of the carbon reduction of various sponge city construction measures. For example, urban green spaces can be divided into common planting types. Based on the amount of fixed carbon per unit area of each planting type (pi) (see Table 3), the area (Ai) or area ratio corresponding to different planting types can be determined and calculated. The amount of fixed CO2 in each planting type can be weighted to give the total urban vegetation carbon sequestration:
Weiwei Shao et al. / Energy Procedia 152 (2018) 1145–1151 Weiwei Shao et al./ Energy Procedia 00 (2018) 000–000
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,
(2)
where Ai is the planting area of different types of green spaces in urban areas, Pi is the planting method, Cpi is the total amount of fixed carbon corresponding to the planting method (kg m-2), and C is the total amount of fixed carbon (kg or t). The parameters used in this method are from relevant scholars’ observational studies of the Taiwan region [7][10]. We will use this method in the future to further analyze urban green space carbon sinks because the Taiwan region is near Xiamen and has a similar climate. Table 3. Amount of fixed CO2 based on the 40-year statistics for different planting methods Planting code
Planting method
Amount of fixed CO2 (kg/m3)
p1
Large and small trees, shrubs, flowers, and plants
1200
p2
Large broad-leaved trees
900
p3
Small broad-leaved trees, coniferous trees, and leafless trees
600
p4
Palms
400
p5
Dense shrubs
300
p6
Perennial vines
100
p7
Ornamental grasses, natural grasses, lawns, and aquatic plants
20
In this study, a preliminarily analysis of carbon reduction caused by the construction of a sponge city, using urban afforestation, the creation of river and lake wetlands, and rainwater resource, was conducted. Carbon reduction from measures such as reduced household electricity consumption, increased pervious surfaces, and drainage pipe network transformation needs to be further quantified. Carbon reduction from the transformation of the drainage network is relatively complex. The improved and increased rate of sewage collection will increase the emission reduction efficiency of pollutant treatment and is planned for use in sponge city design. Upgrading sewage treatment systems will lead to an increase in energy consumption and an increase in carbon emissions. Therefore, the effect of reducing emissions from the wastewater treatment process needs further analysis. 6. Conclusion In China, sponge cities are being promoted nationwide. Sponge city construction has followed the concept of ecological civilization. It will cause direct or indirect emission reductions and alleviate the regional heat island effect. In this study, the city of Xiamen was used as an example to analyze the carbon reduction from increased plant cover in urban areas, the construction of river and lake wetlands, and the use of rainwater resources. The results showed that the carbon reduction from sponge city construction is significant. This supports China’s continued promotion of the construction of sponge cities and the construction of low-carbon cities. Acknowledgments This work was financially supported by the Chinese National Key Research and Development Program (2016YFC0401401), the Chinese National Natural Science Foundation (No. 51522907), and the Research Fund of the China Institute of Water Resources and Hydropower Research (No. 2017ZY02, No. WR0145B502016). References [1] Bai W., Du Q., LV J., Peng C., Liu K. Research on the carbon footprint in the production of common portland cement. Journal of Xi’an polytechnic university, 2013, 27(4), 472-476. [2] Lou W. Study on measurement methods of city carbon emissions: Beijing as a case. Journal of Huazhong University of Science and Technology, 2011, 25(3), 104-110. [3] Gan Y., Yang L., Fu X. Study on the calculation method of carbon footprint for cement manufactures. Shanxi Architecutres, 2012, 38(4), 231232. [4] Zhao C., Liu X. The role of urban green space system in low-carbon city. Chinese Landscape Architecture, 2010, 26 (6) :23-26.
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[5] Carbon emissions trading website. What are the ways of carbon emission reduction in the construction of spongy cities. www.tanpaifang.com, 2016. [6] Fu X., Zhong L. An analysis of energy efficiency and emissions reduction potential of Chengdu’s municipal wastewater treatment plants. World Resources Institute Report, 2015. [7] Zhu K., Zhang Q., Wu P., Feng L. Progression in the methods of accounting carbon sequestration of urban green space. Shaanxi Forest Science and Technology, 2015, 4, 42-47. [8] Duan H., Fan Y. Energy System Integrated Modeling Decarbonization Policy Driven. Beijing: Science Press, 2017. [9] Lin X. Green building commentary assessment handbook. Ministry of the Interior architectural studies, Taipei，2007. [10] Duan X., Wang X., Lu F., Ouyang Z. Carbon sequestration and its potential by wetland ecosystems in China. Acta Ecologica Sinica, 2008, 28(2), 463-469.
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Available onlineatat www.sciencedirect.com Available www.sciencedirect.com Energyonline Procedia 00 (2018) 000–000 Energy Procedia 00 (2018) 000–000
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www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy Procedia 152 Energy Procedia 00(2018) (2017)1145–1151 000–000 www.elsevier.com/locate/procedia
Applied Energy Symposium and Forum 2018: Low carbon cities and urban energy systems, CUE2018-Applied Energy andLow Forum 2018: Low carbon andsystems, Applied Energy Symposium andSymposium Forum 2018: carbon cities and urbancities energy CUE2018, 5–7 June 2018, Shanghai, China urban energy systems, 5–7 June Shanghai, CUE2018, 5–7 June 2018,2018, Shanghai, ChinaChina
Carbon Reduction EffectsSymposium of Sponge City Heating Construction: A Case The 15th International on District and CoolingA Case Carbon Reduction Effects of Sponge City Construction: Study of the City of Xiamen Study of the Xiamen Assessing the feasibility of City usingofthe heat demand-outdoor
Weiwei Shaoaa, Jiahong Liua,b, *, Zhiyong Yangaa, Zhaohui Yangaa, Yingdong Yuaa, Weijia temperature function a long-term districtYang heat demandYuforecast Weiwei Shao , Jiahong Liua,b,for *, Zhiyong Yang , Yingdong , Weijia Liaa* , Zhaohui Li * a c State Key Laboratorya,b,c of Simulation and Regulation of WateraCycle in River Basin,b., China of WatercResources Hydropower I. Andrić *, A. Pina , P. Ferrão , J. Fournier B. Institute Lacarrière , O. Leand Corre State Key Laboratory of Simulation and RegulationResources, of Water Cycle in100038, River Basin, Beijing ChinaChina Institute of Water Resources and Hydropower a a
a
b Resources, 100038, China of Transportation andand Civil Engineering Foshan University, Guangdong China IN+ CenterSchool for Innovation, Technology Policy Research&Beijing - Architecture, Instituto Superior Técnico, Av. Rovisco Pais 1,528000, 1049-001 Lisbon, Portugal b b School of Transportation and Civil & Architecture, Foshan University, 528000, China Veolia Recherche & Engineering Innovation, 291 Avenue Dreyfous Daniel, 78520 Guangdong Limay, France c
Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
Abstract Abstract Abstract This studyheating analyzed the effects the construction of sponge in China, recent years,effective on carbon emissionfor reduction based District networks are of commonly addressed in the cities literature as oneinof the most solutions decreasing the This study analyzed the reduction effects thebuilding construction of These sponge cities inrequire in recent years, on carbon based on the global emission targets and sector. China’s responsibility inChina, reducing carbon emissions. Sponge citiesreduction are built with greenhouse gas emissions fromofthe systems high investments which areemission returned through the heat onsales. the global reduction targets and China’s responsibility in reducing carbon cities could are built with rainwater infiltration, retention, storage, purification, reuse, and drainage facilities to emissions. promote natural Due toemission the changed climate conditions and building renovation policies, heat demand natural inSponge the accumulation, future decrease, rainwater infiltration, retention, purification, reuse,spaces. and drainage facilitiessponge to promote natural accumulation, natural infiltration, and purification of precipitation in urban In the process, city construction, by intensifying the prolonging the natural investment returnstorage, period. infiltration, and natural ofthe precipitation inarea urban spaces. the process, sponge city construction, by intensifying the treatment urban increases urban green expands the urban water surface. The increase in urban greening, The mainofscope ofsewage, thispurification paper is to assess the feasibility of and using the In heat demand – outdoor temperature function for heat demand treatment sewage, increases theand urban and expands urban Thereduction increase in consisted urbaningreening, expansion ofurban wetlands in urban rivers lakes, andarea use of rainwater resources tostudy. carbon theofcity. forecast. of The district of Alvalade, located ingreen Lisbon (Portugal), wasthe used as water a lead casesurface. district effects is 665 expansion wetlands in urban andperiod lakes, andtypology. use ofthe rainwater resources to(low, carbon reduction effects in Xiamen, thedistrict city. Considering the city of asrivers an example andand combining main measures forlead the construction of a sponge city three buildings of that vary inXiamen both construction Three weather scenarios medium, high) and Considering the city of were Xiamen as an example andintermediate, combining thedeep). main measures forthe the construction aheat sponge citythe in Xiamen, our quantitative analysis suggested that urban greening can reduce carbon emissions by error, 66,266.7 tonsofper year, and lake and renovation scenarios developed (shallow, To estimate obtained demand values were our quantitative analysis suggested that urban greening canper reduce 66,266.7 per year, and and river wetlands reduce carbon emissions 962.8 model, tons year. carbon The developed useemissions of rainwater resources in sponge citythe canlake reduce compared withcan results from a dynamic heatby demand previously andbyvalidated bytons thethis authors. river canby reduce carbon emissions bychange 962.8 per year. The use of rainwater resources in of thisChina's sponge city can reduce carbon emissions 2719.1 tonsonly per year. This showstons emission reductions from the could construction sponge cities are The wetlands results showed that when weather isthat considered, the margin of error be acceptable for some applications carbon emissions by 2719.1 tons perlower year.than This shows reductions from the construction China's sponge renovation cities are significant, resulting indemand effective responses to and mitigation of climate change.considered). (the error in annual was 20% forthat all emission weather scenarios However, of after introducing significant, effective responses and mitigation of on climate change.and renovation scenarios combination considered). scenarios, resulting the error in value increased up toto59.5% (depending the weather Copyright 2018 Elsevier Ltd. All rights reserved. The value©of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the Copyright © © 2018 Elsevier Elsevier Ltd. Ltd. All All rights rights reserved. reserved. Copyright Selection peer-review responsibility of the scientific committee Applied Energy Symposium and Forum 2018: Low decrease and in 2018 the number ofunder heating hours of 22-139h the heating of season on the combination of weather and Selection and peer-review under responsibility of the during scientific committee of the(depending CUE2018-Applied Energy Symposium and Selection andscenarios peer-review under responsibility of hand, the scientific committee of Appliedfor Energy Symposium and Forum 2018: on Low carbon cities and urban energy systems, CUE2018. renovation considered). On the other function intercept increased 7.8-12.7% per decade (depending the Forum 2018: Low carbon cities and urban energy systems. carbon cities and urban energy systems, CUE2018. coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and Keywords: City; Urban Green Land;estimations. Wetlands; Stormwater Management; Carbon Reduction Effect improve Sponge the accuracy of heat demand Keywords: Sponge City; Urban Green Land; Wetlands; Stormwater Management; Carbon Reduction Effect
© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +86-10-68781936; fax: +86-10-68483367 Cooling.
* Corresponding Tel.: +86-10-68781936; fax: +86-10-68483367 E-mail address:author. [email protected] E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the Applied Energy Symposium and Forum 2018: Low carbon cities Selection and peer-review under responsibility the scientific Selection peer-review responsibility of the scientific committee of the Applied Energy Symposium and Forum 2018: Low carbon cities and urbanand energy systems, under CUE2018. and urban energy systems, CUE2018. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the CUE2018-Applied Energy Symposium and Forum 2018: Low carbon cities and urban energy systems. 10.1016/j.egypro.2018.09.145
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1. Introduction From a global perspective, the rapid economic development, urbanization, and industrialization of any country is based on the massive consumption of energy. However, unlike in the past, the current problems are not restricted to rapid economic development; environmental problems, such as climate change, are serious global concerns. Because of global warming, extreme weather, such as high temperatures, droughts, and heavy rains, has occurred in many cities. The frequency and intensity of such extreme weather has increased significantly. These changes have made it difficult to sustain resource-consumption-style development, which leads to environmental harm. If we cannot effectively control greenhouse gas emissions, the global warming trend will continue, and humanity will be exposed to unpredictable risks. Therefore, effective actions should be taken to balance economic development with environmental protection. China is a major greenhouse gas emitter in the world. The pressure to reduce carbon emissions worldwide is severe. China’s share of global carbon emissions has increased from 20.9% in 2005 to 27.5% in 2014 [1]. Although the growth rate of carbon emissions has slowed in the past two years owing to low energy consumption, changing the global trend in carbon emissions will be difficult. As a responsible, developing country, China has been actively responding to climate change (Table 1). The 2014 China-U.S. Joint Statement on Climate Change included a clear plan for achieving a peak in CO2 emissions by approximately 2030 [2]. With this agreement, the goal is to reach an early peak in CO2 emissions with plans to increase the share of non-fossil energy sources in primary energy consumption to approximately 20% by 2030. In 2016, China politically supported the signing of the Paris Agreement, which opened a new phase of global cooperation to address climate change. When developing its Thirteenth Five-Year Plan, China adhered to concepts regarding innovation, coordination, green initiatives, openness, and shared development. The plan vigorously promotes low-carbon development and effective actions to address climate change. Table 1. China's responses to global warming Year
Response
2005
CO2 emission reduction targets were proposed in the National Eleventh Five-Year Plan.
2007
The National Plan for Addressing Climate Change was announced.
2009
The National People's Congress passed the Resolution on Actively Addressing Climate Change.
2009
The State Council proposed that the carbon intensity in 2020 be 40%–45% lower than the carbon intensity in 2005.
2012
A greenhouse gas control program was introduced that required a 17% lower carbon intensity in 2015 than in 2010.
2014
The China-U.S. Joint Statement on Climate Change was released in which a 2030 emission peak and non-fossil fuel energy targets were proposed.
2015
China submitted the National Indigenous Emissions Reduction Contribution plan, which proposed to lower carbon intensity by 60% in 2030, based on levels of 2005.
2016
The Paris Agreement was signed and ratified by the Standing Committee of China’s National People’s Congress in September, and China became the 23rd Party to complete the ratification agreement.
China is developing “sponge cities” as a new urban construction mode. A sponge city is a city that acts like a sponge to absorb storm water runoff from impervious surfaces and has good elasticity with regards to adapting to environmental changes and responding to natural disasters. When it rains, a sponge city absorbs, stores, and purifies the water. When required, the stored water is released and added to the urban water supply. Since the launch of China's national strategy for sponge cities in late 2013, the construction of sponge cities has become an important factor in environment friendly construction and economic development. Based on the first group of 16 pilot cities in 2015 and the second group of 14 pilot cities in 2016, provinces have issued guidance on promoting the construction of sponge cities. Cities around China have also developed plans for sponge cities. A sponge city accumulates rainfall in original landforms and uses the ecological background of rainwater and the natural underlying surface of the land, allowing the water to be naturally purified by vegetation, soil, and wetlands. Sponge cities can be flexible, adapt to changes in the environment, and respond to natural disasters. The construction of sponge cities in urban
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development and construction will strengthen planning in, improve management of, and increase control over urban construction; will lead to the adoption of measures such as source abatement, process control, and system governance to cope with the urban non-point source pollution; and involve the use of techniques such as roof greening, permeable paving, swales, rainwater storage ponds, and river and lake wetlands. Sponge cities are constructed to address drought, erosion, water pollution, and the urban heat island effect. The relationship between China's sponge cities and low-carbon development has not been thoroughly explored. The carbon emissions from the construction of sponge cities and the question of whether sponge cities contribute to the reduction of urban emissions require further study. Therefore, an analysis of carbon reductions from the construction of sponge cities can provide in-depth information, which may promote construction of sponge cities to improve a city’s ability to adapt to climate change in China. 2. Overview of carbon reductions from sponge city construction Currently, more than 50% of the world's population is concentrated in cities, with these city dwellers consuming approximately 75% of the world’s energy and producing 80% of its greenhouse gas emissions [3]. Carbon emission sources for cities include the burning of fossil fuels, the oxidation and corrosion of organic materials, and human and biological resources (respiration, tree felling, etc.). Many cities now have their own low-carbon development indicator systems in place to limit carbon emissions in fields such as industry, construction, and transportation. However, the planning and construction of low-carbon cities cannot rely solely on reducing carbon emission sources; an increase in carbon sinks in cities is also needed. Sponge cities, through the combinations of artificial and natural infrastructure, ecological and engineering measures, and surface water and groundwater, can help resolve problems of carbon emissions in urban areas, address malodorous black and odor issues in water, and improve water ecology. At the same time, sponge cities can form urban carbon sinks, regulate the microclimate, and ease the heat island effect. Therefore, the construction of sponge cities can transform urban development concepts and construction methods. Carbon emission reduction in sponge city construction is mainly achieved through processes such as, direct carbon fixation in urban green systems, fossil fuel energy and emission reductions and carbon reduction on hardened ground. 2.1. Direct carbon fixation in urban green systems Urban green systems are the most important carbon sinks in cities. The scattered plants in urban areas that fix CO2 from the air in the plants or soil via photosynthesis form the carbon sinks in urban green systems. Sponge city construction will increase the urban afforested area and the growth of grassland biomass through green roofs, rainwater gardens, sunken green spaces, planted trenches, wetlands, and other green systems. This will increase the absorption of carbon. The enhanced role of carbon sinks will result in direct emission reductions. This can effectively curb and mitigate the urban heat island effect and global climate change, to a certain extent, and at the same time, beautify and improve the living environment, and provide ecological, social, economic, and cultural benefits. 2.2. Fossil fuel energy and emission reduction A sponge city construction includes green roofs, rainwater storage tanks, river and lake wetlands, and grassed swales, as well as ecological reconstruction of roads and communities. Through the construction of sponge cities, the urban heat island effect will be greatly reduced, the community’s ecological environment will be optimized, residents’ use of air conditioners and other electrical appliances will be reduced, and residential and commercial power consumption will decrease. According to relevant results, the community’s energy consumption will be directly reduced by more than 30% [4].
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2.3. Carbon reduction via permeable pavement In the construction of sponge cities, the large amount of impervious surface needs to be reduced through the construction of pervious paving or green spaces. Thus, the amount of cement used will be reduced. The carbon footprint in cement production is high and includes raw material production, raw material transportation, and cement production and processing. The carbon emissions from cement production and processing are mainly from fuel combustion, chemical reactions, and electricity consumption in production. For all types of cement, the carbon emissions from the decomposition of carbonate minerals account for the largest proportion of the total carbon emissions (ranging from 47–56%). According to relevant research results, approximately 100 tons of limestone produced from the decomposition of 100 tons of raw materials for cement will produce approximately 44 tons of CO2 [5]. 2.4. Reduced consumption and emission reduction in sewage treatment Low concentration and low loads will affect the effective operation of the sewage treatment plant, cause unnecessary energy consumption, and reduce efficiency of the sewage treatment system [6]. In their construction, sponge cities can increase the efficiency of waste water facilities through the improvement of the drainage network, increase in the sewage collection rate, optimization of collection systems for sewage treatment facilities (such as the addition of adjustment pools), enhancement of water-saving management, and improvement of the water use efficiency. The amount of clean water ensures that the sewage treatment facilities are operating under optimal design conditions, which improves the efficiency of pollutant emission reduction. 2.5. Carbon reduction through rainwater use Sponge city construction will increase the use of rainwater resources and reduce the consumption of tap water, which will reduce carbon emissions from the production and supply of tap water. Therefore, sponge city construction can change the carbon footprint of the original urban construction methods, and this carbon reduction can be significant. From the above analysis, we can see that through protection and restoration of the ecological environment, the construction of sponge cities can contribute to reduced carbon emissions and consumption. 3. Study area Located in the southeastern part of Fujian Province, China, the city of Xiamen has a land area of 1,699 km2. The average annual precipitation is 1,530 mm, decreasing from northwest to southeast. Xiamen was in the first batch of pilot cities for sponge city construction approved by the state in 2015. Sponge city construction in Xiamen included six aspects: pollution prevention and control, construction of ecological water systems, construction of drainage and flood control systems, construction of garden spaces, construction of roads, and construction of sponge residential communities. Measures and indicators of sponge city construction in Xiamen were divided into 16 units. Through the construction of various management and control units, the construction goals of the entire sponge city were achieved, including control of 70% of the total annual runoff, making the city more green, natural, and flexible. 4. Methods and results
4.1. Estimating the urban carbon reduction effect In 2014, Xiamen had 11,172 ha of green space. According to the construction plan of the sponge city, Xiamen plans to establish 18647.79 ha of green land by 2020, including 5161.09 ha of city parks, 1373.33 ha of regional parks, 1246.41 ha of special parks, 2831.71 ha of linear parks, 508.85 ha of community parks, 1971.15 ha of greenery along streets, and 5543.25 ha of protection zone green space. According to a relevant scholar’s calculations
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[5], green coverage is closely related to the CO2 concentration in the air, and 100 m2 of urban green space can absorb approximately 325 kg CO2 per day. According to this method, we roughly estimated that through the construction of planned green land in the sponge city, the city of Xiamen would achieve a carbon reduction of 66266.70 tons per year.
4.2. Estimation of the carbon reduction from river and lake wetlands Owing to their structural composition, wetland ecosystems play an important role in absorbing atmospheric greenhouse gases and slowing down global warming. The wetland carbon sink formula is [7][8]: (1) where Cs is the amount of carbon fixed in the wetland per year, Si is the area of the wetland (m2), and Pi is the rate of carbon sequestration in the wetland per unit area (g-C m-2 a-1). Some scholars have consolidated sedimentary data from lake and marsh wetlands in China over the past 100 years by consulting wetland surveys and the literature. Table 2 shows the estimated carbon fixation rates for wetlands across China that have been calculated based on their sedimentation rates and sediment composition. Table 2. Rates of carbon sequestration for lake wetlands in China Location
Carbon fixation rate, Pi (g-C m-2 a-1)
Eastern Plain Lake Wetlands
56.67
Mengxin Plateau Lake Wetlands
30.26
Yunnan-Guizhou Plateau Lake Wetlands
20.08
Qinghai-Tibet Plateau Lake Wetlands
12.57
Northeast Plains and Mountain Lake Wetlands
4.49
Through the construction of a sponge city in the city of Xiamen, the areal proportion of Xiamen's rivers, lakes, and wetlands will increase from 6% in 2014 to 7% by 2020, with an increase in area of approximately 16.99 km2 (using the carbon sequestration rate of lake wetlands in the eastern plains). It is estimated that 962.8 tons per year of carbon reduction will be achieved through the construction of river and lake wetlands.
4.3. Estimation of the carbon reduction from the use of rainwater resources Sponge city construction will increase the use of rainwater resources and reduce the consumption of tap water. According to scholars' analyses, producing 1 m3 of tap water requires approximately 0.194 kg of carbon [5][9]. According to the plans for construction of the sponge city in Xiamen, the utilization rate of rainwater resources will increase from 0.5% (approximately 3.163 million m3) of the total water use in 2014 to 2% (17.18 million m3) of the total water consumption by 2020, leading to savings in tap water usage. The use of approximately 14.016 million m3 of rainwater will reduce carbon emissions by approximately 2719.1 tons per year. 5. Discussion Owing to imperfect data, empirical methods were used in this study for the calculations and analysis. In the future, it will be necessary to refine the analysis of the carbon reduction of various sponge city construction measures. For example, urban green spaces can be divided into common planting types. Based on the amount of fixed carbon per unit area of each planting type (pi) (see Table 3), the area (Ai) or area ratio corresponding to different planting types can be determined and calculated. The amount of fixed CO2 in each planting type can be weighted to give the total urban vegetation carbon sequestration:
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,
(2)
where Ai is the planting area of different types of green spaces in urban areas, Pi is the planting method, Cpi is the total amount of fixed carbon corresponding to the planting method (kg m-2), and C is the total amount of fixed carbon (kg or t). The parameters used in this method are from relevant scholars’ observational studies of the Taiwan region [7][10]. We will use this method in the future to further analyze urban green space carbon sinks because the Taiwan region is near Xiamen and has a similar climate. Table 3. Amount of fixed CO2 based on the 40-year statistics for different planting methods Planting code
Planting method
Amount of fixed CO2 (kg/m3)
p1
Large and small trees, shrubs, flowers, and plants
1200
p2
Large broad-leaved trees
900
p3
Small broad-leaved trees, coniferous trees, and leafless trees
600
p4
Palms
400
p5
Dense shrubs
300
p6
Perennial vines
100
p7
Ornamental grasses, natural grasses, lawns, and aquatic plants
20
In this study, a preliminarily analysis of carbon reduction caused by the construction of a sponge city, using urban afforestation, the creation of river and lake wetlands, and rainwater resource, was conducted. Carbon reduction from measures such as reduced household electricity consumption, increased pervious surfaces, and drainage pipe network transformation needs to be further quantified. Carbon reduction from the transformation of the drainage network is relatively complex. The improved and increased rate of sewage collection will increase the emission reduction efficiency of pollutant treatment and is planned for use in sponge city design. Upgrading sewage treatment systems will lead to an increase in energy consumption and an increase in carbon emissions. Therefore, the effect of reducing emissions from the wastewater treatment process needs further analysis. 6. Conclusion In China, sponge cities are being promoted nationwide. Sponge city construction has followed the concept of ecological civilization. It will cause direct or indirect emission reductions and alleviate the regional heat island effect. In this study, the city of Xiamen was used as an example to analyze the carbon reduction from increased plant cover in urban areas, the construction of river and lake wetlands, and the use of rainwater resources. The results showed that the carbon reduction from sponge city construction is significant. This supports China’s continued promotion of the construction of sponge cities and the construction of low-carbon cities. Acknowledgments This work was financially supported by the Chinese National Key Research and Development Program (2016YFC0401401), the Chinese National Natural Science Foundation (No. 51522907), and the Research Fund of the China Institute of Water Resources and Hydropower Research (No. 2017ZY02, No. WR0145B502016). References [1] Bai W., Du Q., LV J., Peng C., Liu K. Research on the carbon footprint in the production of common portland cement. Journal of Xi’an polytechnic university, 2013, 27(4), 472-476. [2] Lou W. Study on measurement methods of city carbon emissions: Beijing as a case. Journal of Huazhong University of Science and Technology, 2011, 25(3), 104-110. [3] Gan Y., Yang L., Fu X. Study on the calculation method of carbon footprint for cement manufactures. Shanxi Architecutres, 2012, 38(4), 231232. [4] Zhao C., Liu X. The role of urban green space system in low-carbon city. Chinese Landscape Architecture, 2010, 26 (6) :23-26.
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[5] Carbon emissions trading website. What are the ways of carbon emission reduction in the construction of spongy cities. www.tanpaifang.com, 2016. [6] Fu X., Zhong L. An analysis of energy efficiency and emissions reduction potential of Chengdu’s municipal wastewater treatment plants. World Resources Institute Report, 2015. [7] Zhu K., Zhang Q., Wu P., Feng L. Progression in the methods of accounting carbon sequestration of urban green space. Shaanxi Forest Science and Technology, 2015, 4, 42-47. [8] Duan H., Fan Y. Energy System Integrated Modeling Decarbonization Policy Driven. Beijing: Science Press, 2017. [9] Lin X. Green building commentary assessment handbook. Ministry of the Interior architectural studies, Taipei，2007. [10] Duan X., Wang X., Lu F., Ouyang Z. Carbon sequestration and its potential by wetland ecosystems in China. Acta Ecologica Sinica, 2008, 28(2), 463-469.