Energy consumption and water use are inextricably linked. Combining research on energy consumption and water use in an urban context provides a scientific basis for the integrated planning of energy and water supply systems. Domestic energy and water are among the most consumed resources in urban environments. Furthermore, domestic resources represent an increasing proportion of the total resources consumed. This paper explores four key indicators of urban energy consumption (UEC) and water use in Beijing and Shanghai for the period of 2000 to 2011. Using correlation analysis, this study establishes the intrinsic relationship between UEC and water use. It also offers an analysis of the consumption trends of these two resources as well as their interactive relationship. The results show that urban domestic energy consumption (UDEC) and water use have a significant linear correlation: UDEC is positively correlated with water use, and the correlation coefficients of Beijing and Shanghai are 0.81 and 0.97, respectively. In Beijing, urban domestic energy and water use per capita are negatively correlated, with the high correlation coefficient of 0.93. In Shanghai, urban domestic energy and water use per capita are positively correlated, with the correlation coefficient of 0.90.

Nomenclature

  • UP

    urban population

  • UEC

    urban energy consumption

  • UWU

    urban water use

  • UDEC

    urban domestic energy consumption

  • UDWU

    urban domestic water use

  • UDECPC

    urban domestic energy consumption per capita

  • UDWUPC

    urban domestic water use per capita

Introduction

In recent years, urbanization has become a major global trend. The increasing population in urban environments as well as quality-of-life improvements have escalated both energy consumption and water use. Urban energy consumption (UEC) is closely related to transportation systems, building systems, and infrastructure (Yao & Pan, 2009; de Casas Castro Marins & de Andrade Roméro, 2013). Urbanization and high-density urban development have a significant impact on energy consumption and, therefore, a nation's energy structure (Parikh & Shukla, 1995; Al-mulali et al., 2013). Urban life, with its demand for transportation and services such as housing and water, is bound to require significant amounts of energy (Salim & Shafiei, 2014). In Chinese urban households, energy consumption is growing rapidly. As a result, the energy consumption structure of China is changing (Yan & Minjun, 2009; Sun et al., 2000). A similar trajectory is visible in the urban water system, which has also been affected by urbanization. The increasing number of water users has led to a growing demand for city water, especially domestic water, adding pressure to urban water supply systems (Wu & Tan, 2012). The vulnerability of water resources in rapidly growing cities has caused concern among many researchers (Vörösmarty et al., 2000; Srinivasan et al., 2013).

The previous research on urban systems has largely focused on a single aspect, such as UEC or water use calculation and analysis. However, the integration of energy and water usage has attracted the attention of many researchers who are involved in city planning and operation (Kahrl & Roland-Holst, 2008; Mohammadi et al., 2008; Khan et al., 2009; Dale et al., 2011). The ‘energy–water nexus’ concept has been investigated extensively and, therefore, increasingly highlighted as an important issue (Siddiqi & Anadon, 2011; Ackerman & Fisher, 2013; Lubega & Farid, 2014; Santhosh et al., 2014a, 2014b; Santhosh et al., 2014a, 2014b). Studies have been carried out to examine the role of energy consumption in urban water supplies, water distribution, and wastewater treatment processes (Kenway et al., 2008; Miller et al., 2012; Nowak et al., 2015). In addition, research has been done on the impacts of water and energy on industry (Schornagel et al., 2012; Kermani et al., 2014) and agriculture (Jackson et al., 2011; Cheng et al., 2013; García et al., 2014). Currently, the improvement of energy and water efficiency is a major concern. The energy used to heat water makes up a large portion of the energy consumed in daily life. Furthermore, water-related energy is used in filters, pumps, dishwashers, and washing machines. Energy consumption in the urban water cycle can be reduced through using water more efficiently (Wolff et al., 2004). Thus, research that considers the consumption of energy and water from an integrated perspective represents a vital emerging trend. Such research can provide a scientific basis for optimizing both energy and water resources.

A number of studies have investigated the relationship between energy and water, but few have analyzed the relationship between urban domestic energy consumption (UDEC) and water use. The aim of this paper is to establish the intrinsic link between domestic energy consumption and water use. Energy consumption can be used to estimate water use, and vice versa. Understanding this link can help optimize residential energy and water supplies. Finding a balance between energy and water use is a vital part of minimizing total resource consumption.

Water and energy resources are critical to the stability and sustainable development of cities, and their availability is affected by global change and climate change. This paper establishes the intrinsic relationship between UEC and water use through correlation analysis. Using energy and water use data from Beijing and Shanghai between 2000 and 2011, we show the interaction relationship between urban energy and water use in the context of rapid urbanization. The findings of this quantitative study provide insight into urban resource consumption and can aid cities in making an effective plan for resource utilization, which is an important part of sustainable urban development.

Methods

The study uses three basic categories of data: urban population (UP), UEC, and urban water use (UWU). We investigate the following four key indicators: derivative calculated, including total UDEC; total urban domestic water use (UDWU); urban domestic energy consumption per capita (UDECPC); and urban domestic water use per capita (UDWUPC). These four indicators are divided into two groups: UDEC–UDWU and UDECPC–UDWUPC. A correlation analysis is carried out for each group. Figure 1 represents the technology roadmap.
Fig. 1.

Technology roadmap.

Fig. 1.

Technology roadmap.

Three categories of data

UP

The UP indicator refers to the current population living in urban areas, including those residing on a temporary basis. The UP data are obtained from China's economic and social statistics database (China's economic and social statistics database, 2011).

UEC

The UEC indicator (China's economic and social statistics database, 2011) refers to the annual energy consumption of all social sectors, including residential life, in urban areas.

A city's total energy consumption comprises its annual energy consumption from all social sectors, or its end-use energy consumption. This measure accounts for the loss of energy incurred during processing, converting, transporting, and managing energy resources. The total energy consumption data (China's economic and social statistics database, 2011) for each city are used to determine the UEC of the study period. Some data conversion was necessary when UEC data were unobtainable. Specifically, we select a typical year and calculate the proportion of UEC among the city's total energy consumption in that year. The proportions for other years are assumed to be the same as that of the typical year. Each year's UEC is calculated as the total energy consumption multiplied by this proportion. This conversion formula is calculated as: 
formula
1
 
formula
2
where is the proportion of UEC accounting for the city's total energy consumption; is the urban energy consumption of the typical year; is the city's total energy consumption in a typical year; is the urban energy consumption of year i; and is the city's total energy consumption in year i.

UWU

The UWU indicator (China's economic and social statistics database, 2011) refers to annual water use in the urban areas. Statistical data for UWU can be found in each city's water resources bulletin (Beijing Water Resources Bulletin, 2011; Shanghai Water Resources Bulletin, 2010). This includes information about annual water supply, water use, and water consumption. In addition, detailed data are available for industry, agriculture, life, and other classifications.

Four key indicators and their calculation methods

UDEC

The UDEC indicator (China's economic and social statistics database, 2011) refers to all types of energy consumed in a year as a result of residential life in urban areas. The city's total domestic energy consumption data (China's economic and social statistics database, 2011) are used to determine the UDEC of the study period when UDEC data are unobtainable. The conversion formula is calculated as: 
formula
3
where is the proportion of UEC among the city's total energy consumption; is the urban domestic energy consumption during year i; and is the city's total domestic energy consumption during year i.

UDECPC

The UDECPC indicator refers to urban residential energy consumption per person per year, and is calculated as follows: 
formula
4
where is the urban domestic energy consumption per capita during year i; is the urban domestic energy consumption of year ; and is the urban population during year .

UDWU

The UDWU indicator refers to urban residential water use per year. The data are taken from China's economic and social statistics database (China's economic and social statistics database, 2011) and each city's water resources bulletin (Beijing Water Resources Bulletin, 2011; Shanghai Water Resources Bulletin, 2010).

UDWUPC

The UDWUPC indicator refers to urban residential water use per person per year, and is calculated as follows: 
formula
5
where is the urban domestic water use per capita during year i; is the urban domestic water use during year i; and is the urban population during year i.

Case study

Study site

Both Beijing and Shanghai have experienced rapid urbanization and population growth over the past decade. Due to the increasing development of these two major cities, the demand for and consumption of energy and water are very high. This is a typical effect of urbanization. Among cities in China, Beijing and Shanghai are the leaders in energy and water efficiency. However, compared with cities in developed countries, they have significant room for improvement. Increases in resource efficiency are expected throughout China in the coming years.

The main data

Basic indicators

  • (1) UP

Figure 2 indicates that the UP of Beijing and Shanghai (China's economic and social statistics database, 2011) has increased rapidly, peaking in 2011. In the 21st century, China has reached the rapid development stage of urbanization. The expanded UP requires additional water and energy to meet its transportation, operation, and household needs.
  • (2) UEC

Fig. 2.

UP of Beijing and Shanghai, 2000–2011.

Fig. 2.

UP of Beijing and Shanghai, 2000–2011.

Because of the absence of statistical UEC data for Beijing, the UEC of Beijing is calculated based on its total energy consumption from 2000 to 2011 (China's economic and social statistics database, 2011). Currently, the Beijing statistical information network (Beijing statistical information network, 2011) only provides comprehensive energy consumption data for the districts and counties in Beijing for 2007, as shown in Table 1. Thus, this research uses the year 2007 as a typical year in order to determine and to estimate the detailed data for other years.

Table 1.

Energy consumption data of Beijing's districts and counties in 2007.

 Energy consumption (million t standard coal)  Energy consumption (million t standard coal) 
The Core Area of Capital Functions 5.93 The Expandable Area of Urban Functions 29.88 
 Dongcheng District 1.83  Chaoyang District 11.85 
 Xicheng District 2.38  Fengtai District 3.42 
 Chongwen District 0.60  Shijingshan District 8.08 
 Xuanwu District 1.12  Haidian District 6.53 
New Urban Developmental Area 19.37 Ecological Conservation Development Area 3.91 
 Fangshan District 8.41  Mentougou District 0.76 
 Tongzhou District 2.12  Huairou District 0.91 
 Shunyi District 3.00  Pinggu District 0.90 
 Changping District 2.67  Miyun County 0.89 
 Daxing District 2.48  Yanqing County 045 
 Economic and technological development zone 0.70  The city's total energy consumption 62.85 
 Energy consumption (million t standard coal)  Energy consumption (million t standard coal) 
The Core Area of Capital Functions 5.93 The Expandable Area of Urban Functions 29.88 
 Dongcheng District 1.83  Chaoyang District 11.85 
 Xicheng District 2.38  Fengtai District 3.42 
 Chongwen District 0.60  Shijingshan District 8.08 
 Xuanwu District 1.12  Haidian District 6.53 
New Urban Developmental Area 19.37 Ecological Conservation Development Area 3.91 
 Fangshan District 8.41  Mentougou District 0.76 
 Tongzhou District 2.12  Huairou District 0.91 
 Shunyi District 3.00  Pinggu District 0.90 
 Changping District 2.67  Miyun County 0.89 
 Daxing District 2.48  Yanqing County 045 
 Economic and technological development zone 0.70  The city's total energy consumption 62.85 

The UEC of Beijing only considers the energy consumption of the Core Area and the Expandable Area. Therefore, to determine the UEC, the energy consumption of the New Urban Developmental Area and Ecological Conservation Development Area are subtracted from the total energy consumption. The result is 35.8 million tons of standard coal. Using formula (1), is calculated as 0.57. The UEC of Beijing can be calculated using formula (2). The UEC of Shanghai is also calculated using this method. The results are shown in Figure 3.
Fig. 3.

UEC of Beijing and Shanghai, 2000–2011.

Fig. 3.

UEC of Beijing and Shanghai, 2000–2011.

The UEC of Beijing shows an increasing trend with a steady growth rate. In Beijing, energy consumption has risen tremendously along with total economic output. It has also experienced significant increases in industrial infrastructure and energy efficiency, triggered by technological advances. Currently, the impact of Beijing's secondary industry on energy consumption is declining, while tertiary industry and residential life have become major factors affecting Beijing's energy consumption. To effectively control energy consumption, tertiary industry and residential energy consumption should be examined closely (Fan & Chen, 2010).

The UEC of Shanghai also shows an increasing trend, but its growth rate is much larger than that of Beijing. With the continuous optimization and adjustment of industrial structure in Shanghai, the proportion of its secondary industry in the economy continues to decline, while the proportion of its tertiary industry is rising. However, compared to the tertiary industry, the secondary industry still has relatively high energy consumption and low energy efficiency (Jin, 2013). In 2006, Shanghai further adjusted its industrial structure, promoting the production-oriented economy to the service-oriented economy. Although the UEC of Shanghai is still increasing, there is a decreasing growth rate.

During the study period, in Beijing, the proportion of tertiary industry in gross domestic product (GDP) increased from 64.8 to 76.1%, and the proportion of secondary industry in GDP decreased from 32.7 to 23.4%. In Shanghai, the proportion of tertiary industry in GDP increased from 52.1 to 58.1%, and the proportion of secondary industry in GDP decreased from 46.3 to 41.5% (China's economic and social statistics database, 2011). In Shanghai, steel, metallurgy, and other industries still accounted for a large share of the economy. As a result, energy consumption is higher in Shanghai than in Beijing.

  • (3) UWU

UWU data (China's economic and social statistics database, 2011) are shown in Figure 4. The UWU of Shanghai was larger than that of Beijing. In 2000, Shanghai began promulgating a water conservation plan and established a water-saving index system (Guoping & Huifeng, 2004). This may help control the amount water consumed from 2000. But, the UWU of Shanghai increased from 2006, and then declined from 2009. Shanghai, as China's economic, financial, and trade center, is in the construction process of an international metropolis. Thus, the urban demand for water quantity and quality is increasing. On the other hand, as the capital of China, Beijing implements strict water management to ensure water security. The UWU of Beijing increased much more slowly, and remained at around 2.5 billion (109) m3.
Fig. 4.

UWU of Beijing and Shanghai, 2000–2011.

Fig. 4.

UWU of Beijing and Shanghai, 2000–2011.

Four key indicators

  • (1) UDEC

In order to calculate the UDEC of Beijing, the domestic energy consumption of the New Urban Developmental Area and Ecological Conservation Development Area are subtracted from the total consumption. We assume that the UDEC accounts for the same proportion (0.57) of Beijing's total domestic energy consumption found for the typical year. The UDEC of each year is calculated using formula (3). The UDEC of Shanghai is calculated using the same method. As shown in Figure 5, both UDECs showed an increasing trend from 2000 to 2011. The UDEC can fit a linear assumption well with a steady growth rate. The UDEC of Shanghai is slightly higher than that of Beijing.
  • (2) UDECPC

Fig. 5.

UDEC in Beijing and Shanghai, 2000–2011.

Fig. 5.

UDEC in Beijing and Shanghai, 2000–2011.

The UDECPC of Beijing and Shanghai are calculated using formula (4). As shown in Figure 6, the UDECPC of both cities show an overall upward trend. This trend is mainly due to quality-of-life improvements resulting from urbanization and economic growth. Therefore, this trend implies an intensification in the per capita demand. The usage of various types of household appliances amplifies energy consumption. Increased use of heating in the winter and air conditioning in the summer has also caused energy consumption to rise. In addition, the number of privately owned cars has increased annually at a rate of more than 1,000 vehicles per day for many years (Songli, 2010), resulting in an increased need for transportation fuel. The UDECPC of Beijing increased by 57.6%, from 283.67 kg of standard coal in 2000 to 427.60 kg of standard coal in 2011. The UDECPC of Shanghai increased by 57.6%, from 243.00 kg of standard coal in 2000 to 424.74 kg of standard coal in 2012. The UDECPC of Shanghai is slightly higher than that of Beijing.
Fig. 6.

UDECPC in Beijing and Shanghai, 2000–2011.

Fig. 6.

UDECPC in Beijing and Shanghai, 2000–2011.

  • (3) UDWU

The UDWU is directly related to urban water supply, water management conditions, and water-saving levels. In addition, the economic conditions, housing quality, and general living standards of residents have an impact on domestic water use. With the development of urban water utilities, expansion of the water supply, and improvement in residents' living standards, the UDWU has continued to increase.

The UDWU of Beijing fell during 2000–2002 (Figure 7) due to three consecutive years of drought. In 2002, the city's annual average rainfall was 413 mm, which is 30.6% less than the average annual rainfall (595 mm) (Beijing Water Resources Bulletin, 2011). The decreased rainfall led directly to decreases in the water supply, from 4.04 × 109 m3 in 2000 to 3.46 × 109 m3 in 2002 (Beijing Water Resources Bulletin, 2011). Simultaneously, industrial water use was still large, resulting in a corresponding reduction in UDWU. In 2003, Beijing's annual rainfall increased, and Beijing's water resources were replenished.
Fig. 7.

UDWU in Beijing and Shanghai, 2000–2011.

Fig. 7.

UDWU in Beijing and Shanghai, 2000–2011.

The UDWU of Shanghai increased from 2000 to 2009 and then began to decline. One of the reasons for this is that the price of water increased in Shanghai in 2009 (Jinglun, 2009). In addition, in 2007, Shanghai endeavored to improve water efficiency by imposing 617 water-saving measures (Wenhui News, 2008). Beijing is located in northern China, where water resources are much scarcer than in Shanghai. Water supply provisions and restrictions implemented in Beijing may explain why its water use is lower than that of Shanghai. In terms of residential water conservation, Beijing has made more progress.

  • (4) UDWUPC

The UDWUPC is calculated using formula (5). Although the UDWU of Beijing increased during the study period, Figure 8 indicates that the UDWUPC declined in most years. The UDWUPC of Beijing declined by 24.3%, from 47.87 m3 in 2000 to 36.23 m3 in 2011. The sudden increase of the UDWUPC in 2003 was caused by the end of the drought in Beijing. The water supply increased, providing for more opportunities for domestic water use. The declining UDWUPC of Beijing has two possible explanations. First, water conservation was better accepted and performed in daily life. For example, the water-saving features of new appliances were more effective. Second, the growth rate of the UP exceeded the growth rate of UDWU. With the total domestic water use divided among a larger population, the domestic water use per capita gradually decreased.
Fig. 8.

UDWUPC in Beijing and Shanghai, 2000–2011.

Fig. 8.

UDWUPC in Beijing and Shanghai, 2000–2011.

Figure 8 shows a comparison of the UDWUPCs of Shanghai and Beijing during the study period. Overall, the UDWUPC of Shanghai increased from 2000 to 2009, and then decreased from 2009 to 2011. The UDWUPC of Shanghai showed an increasing trend overall. Similar to its UDWU, Shanghai's UDWUPC started declining in 2009. In Shanghai, water conservation measures achieved certain results. Individual water-conserving actions may have helped to reduce the UDWUPC, with the effect being reflected as of 2009.

Correlation analysis of energy consumption and water use

The scatterplots in Figures 9 and 10 have the UDEC as the horizontal axis and the UDWU as the vertical axis. The scatterplots in Figures 11 and 12 have the UDECPC as the horizontal axis and the UDWUPC as the vertical axis.
Fig. 9.

Correlation graph of Beijing's UDEC and water use.

Fig. 9.

Correlation graph of Beijing's UDEC and water use.

Fig. 10.

Correlation graph of Shanghai's UDEC and water use.

Fig. 10.

Correlation graph of Shanghai's UDEC and water use.

Fig. 11.

Correlation graph of Beijing's UDEC and water use per capita.

Fig. 11.

Correlation graph of Beijing's UDEC and water use per capita.

Fig. 12.

Correlation graph of Shanghai's UDEC and water use per capita.

Fig. 12.

Correlation graph of Shanghai's UDEC and water use per capita.

Because the UDWU and UDWUPC of Shanghai started decreasing in 2009, correlation analysis was carried out using Shanghai data from 2000 to 2009.

As shown in Figure 11, because the 2002 data (297.75, 38.36) deviate from the overall trend, they were rejected.

Discussion

The UDEC of both Beijing and Shanghai are positively correlated with their UDWUs. The correlation coefficient of Beijing is 0.81, and the correlation coefficient of Shanghai is even higher at 0.97. This indicates that UEC and water use in Beijing and Shanghai shared a similar increasing trend. UEC and water use have certain similarities, and so trends are expected to be linear. Beijing and Shanghai are both major cities where domestic resource consumption is tremendous. In daily life, various correlations can be found between energy consumption and water use, including family cooking, which results in both energy consumption and water use, and the use of air conditioning in the summer, which requires energy as well as water. A clear understanding of the positive correlation between energy consumption and water use is conducive to the planning and design of urban water supply systems, as well as the management of the energy and water supplies. Further measures must be taken to improve urban energy and water efficiency. Energy development as well as water conservation plans have been introduced and implemented in Beijing and Shanghai. When conceiving energy development plans and water conservation plans, it is necessary to consider the planning, control, and supply of energy and water from an integrated perspective.

This research revealed a significant negative relationship between the UDECPC and the UDWUPC of Beijing, with the high correlation coefficient of 0.93. This indicates that cities achieve water conservation at the expense of additional energy consumption. In other words, in water-deficient cities, cities tends to use additional energy in order to save the more precious water resources.

The decrease of Beijing's UDWUPC is partly due to rapid population growth since 2000. The population growth rate exceeded the growth rate of domestic water use. On the other hand, since the 1990s, Beijing has established a number of sewage-treatment and water-recycling facilities. This has enabled Beijing to use recycled water and conserve additional fresh water. Moreover, in preparation for hosting the Olympic Games, Beijing developed a recycled water project in 2001 and eventually began operating a recycled water network. In 2003, the city used 210 million m3 of recycled water, and since then, the use of recycled water has increased annually. In 2012, Beijing used 750 million m3 of recycled water (China's economic and social statistics database, 2011). In terms of domestic water use, recycled water can be used for toilet flushing, cooling, washing, and so on, which can reduce UDWU to a large extent. In addition, Beijing vigorously promoted the development of new water-saving technologies and products. The penetration rate of household water-saving appliances reached more than 85%. From 2001 to 2008, the implementation of water-saving technologies conserved up to 53 million m3 of water (Beijing Municipal Commission of Development and Reform, 2009). Water conservation has become a concern of the whole of society, and is becoming a social custom in Beijing.

The decreasing UDWUPC of Beijing is a beneficial trend. However, during the same period, Beijing's UDECPC increased annually. The use of recycled water led to a reduction in domestic water use; however, in the process of treating and transporting recycled water, energy consumption increased. In addition, certain household appliances are becoming much more common as living standards are improving. Their increasing usage, especially air conditioning systems, has led to a significant increase in domestic energy consumption per capita. Beijing has taken numerous approaches to supplying clean energy, aiming to diversify the energy supply and build an adequate, stable energy infrastructure. A secure and reliable energy supply is crucial to improving the efficiency of energy use. As Beijing strived to achieve energy diversification, its energy demand management efforts shifted to the tertiary industry and domestic consumption.

The UDECPC and the UDWUPC of Shanghai are positively correlated from 2000 to 2009, with a correlation coefficient of 0.90. This means that both of the indicators are showing an increasing trend. Although Shanghai has been committed to improving the efficiency of energy and water usage, as well as to controlling energy consumption and water use in all regards, its energy consumption and water use per capita are still increasing. Cities, such as Shanghai, which do not suffer from water shortage would use more water as well as energy. The UDWU and UDWUPC of Shanghai both started to decline in 2009. This indicates that Shanghai's municipal water conservation measures, such as Shanghai Water Conservation Plan, have gradually paid off. Shanghai is the economic center of China. With its economic development and increasing personal income, the quality of life in Shanghai has greatly improved. Electrification is now widespread, and entertainment options are diverse. The consumption of domestic energy, especially electricity and gas, will certainly be greatly increased (Shurong, 1995).

Considering energy consumption, both Beijing and Shanghai show an increasing trend. Previous work has mainly focused on industrial energy conservation, thus, insufficient attention has been paid to domestic energy conservation. For example, the energy efficiency of some gas and some electric water heaters, which are old products introduced from foreign countries, needs to be improved. If the efficiency of UDEC is improved, the total energy consumption will increase much more slowly. In the aspect of water use, the UDWUPC of Beijing started to decline during the study period, indicating that Beijing has achieved remarkable results in water conservation. Furthermore, the UDWUPC of Shanghai began to decline in 2009, revealing a beneficial trend.

However, further research on the coupling of UEC and water use is still required. Case studies should be carried out for different cities. There are many challenges to generating standardized comparable estimates regarding UWU and energy consumption. The need to make assumptions about water use and energy consumption further complicates such research. Therefore, an annual survey of urban water and energy consumption is needed in order to obtain more accurate data.

Conclusion

In Beijing and Shanghai, urban energy and water use gradually increased over the study period. Analysis of the available urban data revealed that rapid population growth intensified the consumption of both energy and water. Quality-of-life improvements and the use of modern equipment and appliances have led to substantial increases in energy consumption and water use.

This article contributes to previous research on a correlation analysis of UDEC and water use, based on multiple data sources. In Beijing, UDEC is positively correlated with water use, with a correlation coefficient of 0.81; UDEC and water use per capita are negatively correlated, with a high correlation coefficient of 0.93. In Shanghai, UDEC is positively correlated with water use, with a correlation coefficient of 0.97; UDEC and water use per capita are also positively correlated, with a high correlation coefficient of 0.90.

The energy consumption and water use of both cities have a linear relationship. Energy consumption and water use has an even closer interaction in the urbanization process. These findings may provide a scientific basis for urban planning and resources management. Decision makers are recommended to consider energy and water supplies from a comprehensive, integrated perspective.

Acknowledgements

This research work is funded by the Chinese National Natural Science Foundation (No. 51279208 & 51522907). The study was also supported by the Open Research Fund of the State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research.

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