The economic benefits of rainwater-runoff reduction by urban green spaces: A case study in Beijing, China

Journal of Environmental Management 100 (2012) 65e71

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The economic benefits of rainwater-runoff reduction by urban green spaces: A case study in Beijing, China Biao Zhang a, *, Gaodi Xie a, Canqiang Zhang a, Jing Zhang b a b

Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Science, Beijing 100101, China Institute of Agricultural Resources and Agricultural Regional Planning, Chinese Academy of Agricultural Science, Beijing 100081, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 4 May 2011 Received in revised form 30 November 2011 Accepted 17 January 2012 Available online 24 February 2012

Urbanization involves the replacement of vegetated surfaces with impervious built surfaces, and it often results in an increase in the rate and volume of rainwater surface runoff. Urban green spaces play a positive role in rainwater-runoff reduction. However, few studies have explored the benefits of rainwater-runoff reduction by urban green spaces. Based on inventory data of urban green spaces in Beijing, the paper evaluated the economic benefits of rainwater-runoff reduction by urban green spaces, using the rainwater-runoff-coefficient method as well as the economic valuation methods. The results showed that, 2494 cubic meters of potential runoff was reduced per hectare of green area and a total volume of 154 million cubic meters rainwater was stored in these urban green spaces, which almost corresponds to the annual water needs of the urban ecological landscape in Beijing. The total economic benefit was 1.34 billion RMB in 2009 (RMB: Chinese currency, US$1 ¼ RMB6.83), which is equivalent to three-quarters of the maintenance cost of Beijing’s green spaces; the value of rainwater-runoff reduction was 21.77 thousand RMB per hectare. In addition, the benefits in different districts and counties were ranked in the same order as urban green areas, and the average benefits per hectare of green space showed different trends, which may be related to the impervious surface index in different regions. This research will contribute to an understanding of the role that Beijing’s green spaces play in rainwater regulation and in the creation and scientific management of urban green spaces. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Urbanization Urban green spaces Rainwater-runoff reduction Beijing

1. Introduction Between 2009 and 2050, the world population is expected to increase by 2.3 billion, passing from 6.8 billion to 9.1 billion (United Nations, 2009). At the same time, the world urban population is expected to increase by 84 percent by 2050, from 3.4 billion in 2009 to 6.3 billion in 2050 (United Nations, 2010). Furthermore, the trend towards urbanization will appear more serious in developing countries (Montgomery, 2008; UN-Habitat, 2009). Rapid urban expansion leads to the replacement of native vegetation areas, which provide rainwater interception, storage, and infiltration functions, with impervious surfaces, which often results in an increase in the rate and volume of surface runoff of rainwater (Whitford et al., 2001; Mansell, 2003). Climate change may further increase these fluctuations and the flood risk (Villarreal et al., 2004). However, urban green spaces have positive effects on water infiltration and storage in the soil (Beard and Green, 1994; * Corresponding author. Tel.: þ86 10 64888157; fax: þ86 10 64888202. E-mail addresses: [email protected] (B. Zhang), [email protected] (G. Xie), [email protected] (C. Zhang), [email protected] (J. Zhang). 0301-4797/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2012.01.015

Roy et al., 2000), runoff reductions (Bernatzky, 1983; Shepherd, 2006; Cheng et al., 2008), nutrient and pollutant removal (Barret et al., 1998; Shuman, 2004; Deletic, 2005, Hou et al., 2006), and groundwater quality (Gross et al., 1990; Carpenter et al., 1998; Connellan, 2007). Therefore, the creation of more green areas has been forwarded as an answer to the recent calls for a more ecological and greener urbanization (Onmura et al., 2001; White, 2002; Van Herzele and Wiedemann, 2003; Dunnett and Kingsbury, 2004). As the capital of China, Beijing has undergone rapid urbanization (Chai and Ta, 2009), the built-up area having spread from 109 km2 in 1949 to 1350 km2 in 2009 (National Bureau of Statistics of China, 2009). The rapid urban extension has altered natural hydrological processes and led to an increase in the rate and volume of surface runoff of rainwater (Wang and Li, 2001; Liu, 2009). Reducing the high runoff during rainfall and increasing rainwater harvesting as an alternative water supply have become important tasks for city managers. Although some studies have found that the green areas in Beijing exert a positive impact on reducing stormwater runoff (Ye et al., 2001; Zhang et al., 2003; Hou et al., 2007; Tian et al., 2008), few investigations have established

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the economic or ecological benefits of rainwater-runoff reduction by urban green spaces (Cheng et al., 2008). Since the positive roles of urban green spaces in the hydrological cycle have been underestimated, greater attention has been paid by city managers to the construction of drainage facilities, which has resulted in an increased financial burden and reduced water resources. The quantification and valuation of ecosystem services can permit a direct comparison between alternative land-use options and facilitate a cost-benefit analysis of related policies (McPherson et al., 1997; Tyrväinen and Miettinen, 2000; Jim and Chen, 2009). The main purpose of the paper is to assess the economic benefits of rainwater-runoff reduction by urban green spaces and to provide a reference point for public and government organizations. This study had the following objectives: (1) to evaluate the functionality and value of rainwater-runoff reduction by the green spaces in Beijing’s built-up areas, and (2) to analyze the spatial variation of rainwater-runoff reduction benefits in different regions. This work will contribute to an understanding of the role that Beijing’s green spaces play in rainwater regulation and to the creation and scientific management of urban green spaces. 2. Materials and methods 2.1. Study area Beijing is located in the north of China at 39 380 e41050 N. It is in the temperate climatic zone, with a mean annual temperature of 12  C (Li et al., 2005). The city has an average precipitation of 554.5 mm, about 80% of which is concentrated in JuneeSeptember (Sun et al., 2007). Under the scenario of global climate change, Beijing has been suffering from a gradual decrease in annual precipitation since 1950 (Yue, 2007). In addition, Beijing has a total area of 16,807 km2 and a population of about 16.95 million, with an average population density of 1033 people/km2 (Beijing Municipal Statistical Bureau, 2010). Its administrative area comprises 14 districts and 2 counties. The city is divided into three zones: the city center (Dongcheng and Xicheng districts), main urban area (Chaoyang, Fengtai, Haidian, and Shijingshan districts), and suburban area (Changping, Daxing, Fangshan, Huairou, Mentougou, Pinggu, Shunyi, and Tongzhou districts and Miyun and Yanqing counties). Since the Reforms and Opening-up policy1 were implemented, Beijing has undergone rapid urbanization. Mu et al. (2007) reported that, the urban area of Beijing was 183.84 km2 in 1973, and it increased to 1209.97 km2 in 2005; the built-up area has increased by 1026.13 km2 during the past 32 years, having expanded at a rate of 32.07 km2 per year. Owing to the fast urbanization, natural ecosystems are being increasingly replaced by an impervious urban surface. The spatial distribution patterns of the impervious surface exhibit a spatial gradient, increasing from the city outskirts to the inner urban areas (Xiao et al., 2007). Impervious surfaces increase the speed and volume of water running off a site, while decreasing the quality of that water and highly modifying the hydrology of urban areas (Shepherd, 2006). A greater proportion of rainfall becomes surface-water runoff, which results in increased peak flood discharges and degraded water quality through the picking up of urban street pollutants (Haughton and Hunter, 1994). In addition, the impervious surfaces and high extraction of water often cause the groundwater levels of many cities to fall (Bolund and Hunhammar, 1999). Rain-runoff coefficient is the percentage of precipitation that appears as runoff. Fig. 1

70 65 60 55 50 45 40

150

200

250

300

350

400

Fig. 1. The runoff coefficient in Beijing before and after the 1970s. Source: Liu (2009).

shows that there was a significant rise (4e8%) in the runoff coefficient before and after the 1970s in Beijing. The quality of runoff from road surfaces is lower than that of natural rainwater (Hou et al., 2006), and the groundwater table declined greatly from 16.42 m in 2001 to 24.07 m in 2009 because of excessive water withdrawal (see Fig. 2). To reduce the high runoff during rainfall, the urbanized areas need to build more and more rainwater-drainage systems, which lead to a greater financial burden. As seen in Fig. 2, there was a significant increase in the total length of rainwater drainage pipes in Beijing, from 2999 km in 2001 to 4849 km in 2009. Vegetated areas have positive benefits on water infiltration and storage in the soil, runoff reduction, nutrient and pollutant removal, and groundwater quality. The total area of green space was 61,695 ha in 2009, of which 29.3% was represented by public green space, 13% by affiliated green space, 24% by protective forest, 12% by residential green space, and 19.7% by roadside green space; that amounts to a total green space area of 60,472 ha. The remaining 2% consisted of productive green space. Fig. 3 shows the distribution of the different green-space types in Beijing. 2.2. Data The present study adopted the seventh survey data of green spaces of Beijing, which was produced by the Beijing Municipal Bureau of Landscape and Forestry applying 3S technologies 5000

4500

The length of rain drainge (a) The level of ground water (b)

-15

-17

4000

-19

3500

-21

3000

-23

2500 1 China’s reform and opening up policy was launched in December 1978, and it aimed, on the one hand, at promoting exports and, on the other, at protecting the domestic market (Srivastava, 2008). The policy has fostered China’s economic modernization.

100

2001 2002 2003 2004 2005 2006 2007 2008 2009

-25

Fig. 2. The length of rain-drainage pipes and the groundwater level from 2001 to 2009 in Beijing. Sources: (a) Beijing Statistical Bureau (2010); (b) Beijing Municipal Water Conservancy Bureau (2003-2009).

B. Zhang et al. / Journal of Environmental Management 100 (2012) 65e71

67

Fig. 3. The spatial distribution of green spaces in Beijing.

(Geographic Information System, Remote Sensing, and Global Positioning System) and employing field investigation in 2009. There are 28,425 green-space patches, including 2226 public green-space patches, 1456 protective forest patches, 5563 roadside green-space patches, 80 productive green-space patches, and 10,932 affiliated green-space patches. The spatial location (latitude and longitude), area, green coverage, plant growth and species composition of each green-space patch were collected. The Beijing Forestry Survey and Design Institute assessed the survey data quality and certificated a pass rate of 98%. These spatial and attribute data are stored in the green-land resource database on the Web-based Geographic Information System (GIS), and managed by the Beijing Forestry Survey and Design Institute. This study mainly focuses on the rainwater regulation function of 28,425 green-space patches, and the spatial distribution of these green-space patches was generated using ArcGis 9.0 software (see Fig. 3). 2.3. Amount of rainwater-runoff reduction The soft ground of vegetated areas allows water to seep through, and the vegetation takes up water and releases it into the air through evapotranspiration (Bolund and Hunhammar, 1999). Rainwater-runoff reduction is the benefit whereby green spaces can store more rainfall runoff than hard surfaces, and this lowers the risk of flooding and improves the quality of water in the environment. The retention capacity of rainwater runoff in green spaces has a close correlation with the soil’s physical properties, soil moisture,

saturated hydraulic conductivity, and precipitation characteristics (Yu, 2004). The runoff coefficient is often considered a constant value (Sen and Altunkaynak, 2006). In the Beijing region of China, the rainwater runoff coefficient of green spaces was often 10%, and the hard surface was 80% (Yin, 2009). However, soil type is very important in the runoff-reduction role of green spaces. Fasterinfiltrating soils, such as sandy soils, have lower runoff coefficients than slower-infiltrating ones, such as clays. Ma (2007) measured the soil permeability of different green-land types in Beijing and found greater differences, using the ring-sampling method and multiple variance analysis method. Therefore, we can determine the runoff coefficients of different green space types in Beijing based on their soil infiltration rates.

ggi ¼

rs  gs ri

(1)

where ggi is the adjust runoff coefficient of the ith green-space type (%), ri is the soil-infiltration rate of the ith green-space type (mm/ min), rs is the standard value of soil-infiltration rate in Beijing (rs ¼ 10 mm/min), ggi is the standard runoff coefficient of green space (gs ¼ 10%), i is the number of green-space types (i ¼ 6). In addition, with an increase in expected precipitation, there will be increased surface runoff (Gill et al., 2007). According to the statistical data of the Beijing Municipal Water Conservancy Bureau (2009), Beijing had 448 mm of precipitation in 2009, with the Pinggu district having the highest (562 mm) and Yanqing County the lowest rainfall (351 mm). The rainfall of the remaining districts or counties was obtained from the Beijing Water Resources Bullet in

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2009. Thus, the amount of rainfall-runoff reduction of the green space can be shown as follows:

DW ¼

n X

  0:001 ghi  ggi Ri Ai

(2)

i¼1

where DW is the amount of runoff reduction (m3/yr), n is the number of green-space patches (n ¼ 28,425), ghi , and ggi are the runoff coefficients of the hard surface and green space, respectively. Ri is the average annual precipitation in different green-space patches (mm), and Ai is the area of the ith green-space patch (m2). 2.4. Value of rainwater-runoff reduction In urban areas, the displacement of open land by the impervious surfaces of streets, driveways, and buildings intensifies the rainfall peak discharge, thereby increasing the risk of flooding. Strategies for reducing the high runoff during rainfall and increasing retention include storage reservoirs and ponds, in which water can be temporarily stored (Ferguson, 1998; White, 2002), and green areas, where water can infiltrate and evaporate (Mentens et al., 2006). Therefore, we assume that the service of rainwater storage by green spaces could be replaced with a reservoir, the economic benefit of rainwater storage could be viewed as the replacement cost2 of the reservoir, and its value can be calculated by the volume and unit cost of the reservoir (P1). In recent years, the unit cost for reservoirs in Beijing has risen to 7.73 RMB/ m3 (Zhang et al., 2010). In addition, grassed areas are effective in removing sediment and nitrogen bound to the sediment (Deletic, 2005). Barret et al. (1998) determined the reduction effect in suspended solid matter of two grassed strips alongside a highway to be 85%, and they found a 31e61% decrease in total phosphorus (P), total lead (Pb), and total nitrogen (N). Given continuous urban expansion and increased road use leading to more pollutants entering the stormwater system, this form of green space should be viewed as a valuable resource (Fam et al., 2008). In Beijing, the water quality in green areas is superior to the runoff from roofs and roads (Hou et al., 2006), and it is often used as reclaimed water for green-land irrigation and vehicle washing. Therefore, the urban society avoids the cost of runoff purification in absence of the service of rainfall-runoff reduction by green spaces, we can view the benefit of reclaimed water as the avoided cost3 of runoff purification, and its value can be estimated by the volume and price of reclaimed water (P2). It has been reported recently that the price of reclaimed water was 1 RMB/m3 in Beijing (Liu and Chu, 2007). Since the green spaces in Beijing can provide these services of rainwater storage and runoff purification, their economic benefits can be multiplied by the additive prices of reservoir and reclaimed water, and the valuation method of runoff reduction by green spaces can be described by the following equation:

V ¼

n X

DWi *ðP1 þ P2 Þ

(3)

patch (m3/yr), P1 and P2 are the unit prices of reservoir and reclaimed water in Beijing (RMB/m3), respectively. 3. Results and discussion 3.1. The amount of rainwater-runoff reduction Beijing is located on the eastern rim of the Eurasian land mass, and has a green spaces area of 61,695 ha in built-up area. Fig. 3 shows that, Beijing’s green spaces are mainly distributed in such inner-city area as Dongcheng district, Xicheng district, Shijingshan district, Chaoyang district, and Haidian district and Fengtai district. The protective forest is scattered outside the main urban area, and the public green space concentrated in the northern regions. The residential green space and affiliated green space represent mosaic distribution characteristics in the built-up areas. The vegetated area could store more rainwater than hard surface in a heavy rainstorm, which reducing runoff loss and the risk of flooding. Based on equation (1), the rainwater-runoff coefficients of every green-space type were determined and showed in Table 1. The residential green space shows the lowest runoff coefficient and the roadside green space the highest, other types of green spaces have the lower runoff coefficients. According to equation (2), we estimated the total volume of rainwater runoff reduced by Beijing’s urban green spaces was to be 154 million cubic meters, and the amount of reduced runoff per hectare green space was 2494 cubic meters. The retention capacity of vegetation largely depends on a combination of such factors as land-cover type, soil, and precipitation. The water-conservation capacities of urban forests in China overall and in Beijing have been estimated to be about 3000 m3/ha (Wu and Su, 2002) and 1373 m3/ha (Zhang et al., 2009), respectively. However, there is higher evapotranspiration in the Beijing area than in China as a whole. If we take into account the water loss from evapotranspiration by vegetation (evapotranspiration rate 50e75%) (Li, 1997), the water-storage capacity of urban green spaces in Beijing ranges from 624 to 1247 m3/ha. In addition, the simpler community structure of urban green spaces maybe also confine the retention capacity; accordingly, we conclude the result of 2494 m3/ha is more accurate. Moreover, Beijing suffers from a severe shortage of water resources (Zhang, 2004). The annual demand for water in the ecological landscape of Beijing has been reported as 161 million cubic meters (Wei and Wang, 2009), which means that the amount of rainfall storage of the green spaces is almost equal to the water demand. Therefore, the results suggest that the green spaces in Beijing can make a great contribution to the saving of water resources and maintenance of the city landscape. It is also necessary to analyze the spatial variations in the runoff regulation function of green spaces in different areas. The amount of rainwater runoff reduced by grass spaces in different districts or counties can be seen in Fig. 4. The grass space of Chaoyang district had the highest contribution, at approximately 31.3 million cubic meters of rainwater runoff, accounting for 20% of the total amount of reduced runoff. The next were the green spaces of Haidian and

i¼1

where V is the economic value of rainwater-runoff reduction (RMB/ yr), DWi is the amount of runoff reduction in the ith green space

2 Replacement Cost: ecosystem services could be replaced with human-made systems; an example is natural waste treatment by marshes which can be (partly) replaced with costly artificial treatment systems (de Groot et al., 2002). 3 Avoided Cost: ecosystem services allow society to avoid costs that would have been incurred in the absence of those services. Examples are flood control (which avoids property damages) and waste treatment (which avoids health costs) by wetlands (de Groot et al., 2002).

Table 1 Adjusted coefficients of rainwater runoff of different green-space types in Beijing. Green-space type

Soil infiltration ratea (mm/min)

Rainwater runoff coefficient (%)

Public green space Roadside green space Residential green space Affiliated green space Defensive forestry Productive green space

8.25 3.95 10.09 8.23 7.38 8.7

12.1 25.3 9.9 12.2 13.6 11.5

a

Source: the average value of infiltration rates in different soil depth (Ma, 2007).

B. Zhang et al. / Journal of Environmental Management 100 (2012) 65e71

69

Fig. 4. The amount and value of rainwater runoff reduction by the green spaces in different areas of Beijing.

Shunyi, which could reduce 26.4 million and 18.4 million cubic meters rainwater runoff, respectively, which corresponding to 17% and 12% of the total. The grass spaces in Fengtai district and Tongzhou district could store 13.1 million and 10.2 million cubic meters of runoff, respectively. The green spaces in other districts and counties made less of a contribution to runoff reduction. The grass space of Mentougou district was a relatively minor contributor to rainwater runoff reduction (only 1.37 million cubic meters). Therefore, the grass spaces of Chaoyang, Haidian, Shunyi, Fengtai and Tongzhou were the main contributors of rainwater runoff reduction, and their cumulative ratio reached 65%. In Beijing, the green spaces in the districts of Chaoyang, Haidian, and Shunyi constituted 45.7% of the total green-space area. Thus, the area of green space has a great influence on the benefits of rainwaterrunoff reduction in different regions of Beijing. However, in terms of per hectare of green space, the greatest rainwater-storage capacity was in the districts of Xicheng and Dongcheng, followed by Shijingshan, Fengtai, Chaoyang, and Haidian; the lowest was the green spaces in Yanqing county and Huairou district (see Fig. 4). The runoff regulation capacities of different regions could be affected by the areas of green vegetation and hard surface. Xiao et al. (2007) found that the distribution patterns of urban impervious surfaces in Beijing exhibit a spatial gradient, which increases in value from the city outskirts to the inner urban areas. Perhaps there is a relation between the rainwater-storage capacity of green spaces and the spatial distribution patterns of urban impervious surfaces. 3.2. The value of rainwater-runoff reduction In the last decade, extreme climate events and meteorological disasters, such as droughts, floods, and high temperatures, have frequently occurred in Beijing (Zheng et al., 2000). The role of green spaces in reducing the risk of floods and the heat island effect has attracted public attention. Pricing the service of rainwater runoff reduction by urban green spaces can improve public awareness of ecosystem services and the sustainable utilization of the green spaces in Beijing. We estimated the economic value of runoff

regulation based on equation (3). The result showed that, the total economic benefit of rainwater-runoff reduction in Beijing’s green spaces was equal to 1.34 billion RMB in 2009, and the monetary value provided by per hectare of green spaces was 21.77 thousand RMB. However, there were great variances in the relative economic contributions of different types of green spaces. The public green space had the highest contribution, at approximately 41.86 million RMB, accounting for 31% of the total value. The next was defensive forestry and residential green space, which provided about 29.53 million and 27.67 million RMB, respectively. The affiliated green space and roadside green space had the minor proportion of the total value (19.06 million and 13.49 million RMB), and the economic benefit of runoff reduction provided by the productive green space was only 2.78 million RMB. The economic contributions of six types of urban green space were closely related to the proportions of their areas. According to the code for management of landscape greening in Beijing (Beijing Municipal Bureau of Landscape and Forestry, 2008), the per year maintenance cost of grass space in first grade is 9 RMB/ m2, and the maintenance cost per year in second and third grade is 6 and 4 RMB/m2, respectively. If we refer to the middle standard of green-space maintenance (6 RMB/m2), the total maintenance cost of the green spaces in Beijing was 1.78 billion RMB/a, which corresponds to just 1.3 times the economic value of rainfall-runoff reduction. However, it is worth noting that a green-space system can provide a variety of ecosystem services except rainwater runoff reduction, there are also significant direct and indirect benefits (Jim and Chen, 2009). Thus, the value of rainwater-runoff reduction can almost offset the maintenance cost of green spaces, which underlines the great importance and necessity of creating green spaces in urban areas. Moreover, specific knowledge about the economic benefits of urban green spaces in different regions can contribute to the policy design for urban environmental management and ecocompensation. Therefore, it is important to analyze the economic benefits of green spaces in different areas regarding the rainwater runoff regulation. The total and average values of

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rainwater runoff reduction in different districts or counties were showed in Fig. 4. From a regional perspective, the districts of Chaoyang, Haidian, Shunyi and Fengtai constituted the largest proportion (together nearly 58%) of the total value, and the green spaces in Tongzhou, Changping, Shijingshan and Fangshan districts provided a larger portion of the total benefits. The green spaces in other areas, including Yanqing, Pinggu, Dongcheng, Xicheng, Miyun, Huairou and Mentougou together generated less than 11% of the runoff regulation value (see Fig. 4). However, the average value per unit area did not follow the same order. The highest was the green spaces in Dongcheng and Xicheng districts, which was larger than 24 thousand RMB/ha. The economic benefits of runoff reduction of per unit area in Chaoyang, Haidian, Shunyi, Fengtai and Shijingshan ranged from 20 thousand to 24 thousand RMB/ha. And the green spaces in Changping, Daxing, Yanqing, Huairou and Mentougou had the minor economic value of runoff reduction (lower than 20 thousand RMB/ha). We concluded therefore that, there may be a relationship between the increase in average value of runoff reduction from the city outskirts to the inner urban areas and the spatial gradient of urban impervious surfaces in Beijing. 4. Conclusions Under the scenario of global climate change and rapid urbanization, clear guidance is needed for local authorities and the public on how best to recognize and manage urban green spaces. A suitable green-space system can provide a variety of ecosystem services. Especially such ecosystem services as infiltrating stormwater and purifying water are important for the urbanized areas to reduce flood and drought impacts. However, the lack of information on the magnitude and value of these services has hindered the recognition and management of urban green spaces. The present study showed, the volume of rainwater stored by the urban green spaces in Beijing was to be 154 million cubic meters or 2494 m3/ha. The total economic benefit was equal to 1.34 billion RMB in 2009, and the value provided by per hectare of green space was 21.77 thousand RMB. In addition, we found that the benefits of rainwaterrunoff reduction produced by urban green spaces varied in different districts or counties. The green spaces could provide significant economic value of rainwater-runoff reduction. Therefore, Beijing could profit from improved rainwater drainage through soft ground since the building and maintenance of a stormwater-drainage system involve large costs. In addition, the present study provides several lessons for policy, practice, and research in developing new urban green spaces. Policies could be used to encourage the optimal structure and composition of urban green spaces through green-space strategies. Urban green spaces should be multifunctional, and their value has to be properly appreciated. We should give adequate attention to urban green spaces that offer important services and build up mechanisms of economic compensation for the people who conserve those spaces. Therefore, climate change and urban sprawl provide opportunities as well as threats for urban green spaces, city managers should pay more attention to the role of urban green spaces in rainwater regulation and the scientific management of urban green spaces. Acknowledgments This research was funded by the Beijing Municipal Bureau of Landscape and Forestry and Major State Basic Research Development Program of China (No. 2009CB421106). We thank the Beijing Forestry Survey and Design Institute for allowing the use of Beijing’s green spaces inventory data.

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