Driving factors for decoupling water resources ecological footprint and economic growth in water-deficient cities dominated by agriculture

Nowadays, the depletion of natural resources and environmental pollution have affected the stability of the human living environment and restricted economic development (Phan 2022). Urban sprawl increases the incomes of residents while further exacerbating the destruction of resources and the environment (Kambu et al. 2022). Economic growth without deterioration of environmental quality is considered to be the best relationship between the economy and the environment. That means the decoupling between economic growth and the water environment. China is one of the 13 water-scarce countries in the world. Therefore, it is important to study the harmonious development of urban economic growth and the water resources environment to solve the contradiction between China's sustainable economic development and the water resources crisis. To explore effective ways to solve this issue, a series of studies have been conducted by relevant institutions and research scholars around the world, including water resource quantification and evaluation systems, water resource and economic development relationships, and their impact mechanisms.

The Ecological Footprint was first proposed by a Canadian ecological economist Willam Rees (1992) in 1992 and refined by his student Wackernagel (1999) as a measure of the extent to which humans use natural resources and the function of life support services provided by nature to humans. This method measures the sustainability of a region by estimating the size of the ecologically productive space required to sustain human consumption of natural resources and assimilate human-generated waste. Comparing this with the ecological carrying capacity of a given population area provides a new way of thinking about the quantitative evaluation of sustainable water resource use. Marti used data envelopment analysis to calculate the environmental efficiency of 45 African countries using the ecological footprint and population as inputs and Gross Domestic Products as outputs (Marti & Puertas 2020). Huang et al. (2008) proposed an ecological footprint model for water resources based on the ecological footprint model, which provides a new approach to quantitatively evaluate the sustainable use of water resources. Su et al. (2022) investigated the characteristics of Japan's water ecological footprint, and compared it with the water ecological footprint of China. The results showed that Japan's agricultural water ecological footprint efficiency was the lowest, and the domestic water ecological footprint efficiency was the highest.

Quantitative evaluation methods for water resources and economic development generally use methods such as the Gini coefficient, Environmental Kuznets curves (EKCs), and decoupling analysis. The Gini coefficients reflect the overall match between regional water resources and socioeconomic status but do not reflect spatial variation (Han et al. 2020). The EKC hypothesis has been the most common and widely studied, but some scholars argue that in some countries or regions, the EKC does not exist (Akbostancı et al. 2009). Some scholars argue that current studies of EKC only describe the phenomena of changes to environmental quality and economic development without analysing the mechanisms that exist between them. Decoupling analysis is the dominant research method in the environmental field because it is simple to determine and does not require much data. The decoupling theory was originally proposed by the OECD in 2002 (OECD 2002), the core principle of this method is that decoupling occurs when the interrelationship between two (or more) physical quantities that have a relationship is weakened (or non-existent). Tapio (2005) defined the critical value of the decoupling state, which is the ratio of the growth rate of environmental stress to the growth rate of socioeconomic growth, as 1, and classified the decoupling state as strong decoupling, strong negative decoupling, weak decoupling, weak negative decoupling, expansive negative decoupling, expansive coupling, recursive decoupling, and recursive coupling. When decoupling analysis is applied to the field of resources and the environment, this method can quantify the relationship between resources, environmental loads, and economic growth. Firstly, the decoupling theory has been used extensively in studies on energy consumption, Wang identified decoupling states for 186 countries in the world, high-income countries initially realized the most desirable strong decoupling, while decoupling states of upper-middle-income and lower-middle-income countries were rather not ideal enough (Wang & Wang 2020). Then, because of the characteristics of the Tapio decoupling model, it is considered the best way to study the relationship between water resources and economic development. Chang applied the Tapio decoupling model to examine the relationship between policy implementation and the performance of water utilization and treatment from 2008 to 2017, and the results showed that policy implementation improved water utilization and treatment efficiency (Chang & Zhu 2021).

Laspeyres and Divisia decomposition are the two most commonly used methods for index decomposition analysis. LMDI, a branch of Divisia, is valued among the many decomposition techniques owing to its full decomposition, lack of residuals, ease of use, consistency of multiplicative and additive decomposition, uniqueness of results, and ease of understanding, and is now widely used in many fields (Ang & Zhang 2000). Tian used the LMDI method to clarify that total water use intensity and the level of development of the water treatment industry were the main factors in wastewater discharge reduction (Tian et al. 2023).

The city's total multi-year average water resources in Zhangjiakou were 1.390 billion m³ (2006–2015), with a per capita water resource of approximately 322 m³, which is below the 500 m³ severe water scarcity line established by the United Nations Commission on Sustainable Development study, making it an area of severe water scarcity. Using the Lorenz Gini coefficient and the imbalance index model, Han et al. (2020) showed that Zhangjiakou's water resources and economic development have gradually changed from a ‘complete mismatch’ to a ‘relative mismatch’, the faster the economic growth rate in counties with approximately scarce water resources. Deng et al. (2020) used a grey correlation model to calculate the drivers of water use structure evolution. This suggests that population growth, urban expansion, and ecological changes are important drivers of water use structures. In summary, previous studies have lacked continuous analysis of time trends between water resources and environmental quality. Most scholars analysed the relationship between water resources and the economy at the macro level, with little research on specific parameters and their critical ranges, which led to unclear approaches in policy recommendations. Therefore, it is difficult to apply the results of these studies to specific plans. This study breaks away from the traditional broad policy recommendations and clearly indicates the critical factors and specific values to solve the problem.

In this study, we aim to analyze the spatial and temporal patterns of water resources and economic growth based on basic data from 16 districts (counties) of Zhangjiakou City between 2006 and 2015, using the Tapio decoupling model to quantitatively evaluate the decoupling relationship between water resources and economic growth. We used the LMDI model and mathematical and statistical analysis methods to identify the key factors affecting the decoupling relationship between water resources and economic growth. Finally, in order to address water resources that limit economic growth, we can increase mechanized agricultural inputs.

Zhangjiakou has a temperate continental monsoon climate, with an average altitude of approximately 1,200 m above sea level, a total multi-year average water resource of approximately 1.390 billion m³, and a multi-year average per capita water resource of 321.69 m³/person, which classifies the region as a severe water shortage area according to the 500 m³ severe water shortage line established by the United Nations Commission on Sustainable Development. At the same time, Zhangjiakou is also a base for the protection of green agricultural and sideline products in Beijing and Tianjin. More than half of Beijing's vegetable supply comes from Zhangjiakou in summer. There is a total of 4.69 million people, with an annual GDP of 136.3 billion yuan and a per capita GDP of 30,840 yuan, compared to national and Beijing GDP per capita of 49,229 and 106,497 yuan, respectively, in the same period, almost two-thirds of the national average and one-thirds of the Beijing average. According to the income grouping criteria published by the World Bank, Zhangjiakou City was classified as an upper-middle-income region in 2015. The extreme scarcity of water resources and economic laxity are the main characteristics of Zhangjiakou, which is dominated by agriculture.

This study used water resources ecological footprint, LMDI, and mathematical statistics method. The water resources ecological footprint model was applied to analyse and evaluate the status of water resources in Zhangjiakou. Meanwhile, economic data of Zhangjiakou districts and counties were collected, and the Tapio decoupling model was applied to evaluate the association between water resources and the economy in Zhangjiakou. The LMDI model and mathematical statistics model were used to identify the key factors. The data for this study were obtained from the Zhangjiakou City Water Resources Bulletin and the Zhangjiakou City Economic Yearbook from 2006 to 2015. To avoid data errors caused by inflation, the economic yearbook data were processed using the deflator method to eliminate errors.

ψ is the ratio of the average production capacity of water resources in a region to the average production capacity of world water resources. ⁠. ν is water volume per unit area in Zhangjiakou, ν_g is the global water per unit area. Based on the calculations, Zhangjiakou City's yield factor of water was 0.12.

In summary, on the time scale, the number of water-saving irrigation machines, the total power of agricultural machinery, agricultural water pumps, agricultural plastic film use, mulch use, total industrialized operation, industrialization rate, and tourism numbers all show a significant upward trend concerning water resource ecological footprint and an opposite trend to GDP.

As shown in Table 2, the decoupling states of Zhangjiakou districts and counties during the study period were significantly different: (1) Guyuan, Zhangbei, Shangyi, Huai'an, Huailai, Chicheng, Wanquan District, and Kangbao counties showed strong decoupling in general; specifically, five districts and counties, namely Zhangbei, Shangyi, Huailai, Chicheng counties, and Wanquan District, showed strong decoupling from 2006 to 2009, from 2010 to 2012, and from 2013 to 2015. The decoupling states of Zhangbei, Shangyi, Huailai, Chicheng, and Wanquan counties from 2006 to 2009, 2010 to 2012, and 2013 to 2015 are all strongly decoupled, which shows a decrease in the ecological footprint of water resources but an increase in socioeconomic development. In Guyuan and Huai'an counties, there was only one weak decoupling from 2010 to 2012, which was a strong–weak–strong decoupling in that order. Kangbao County experienced expansive negative decoupling from 2006 to 2009, and then quickly adjusted to strong decoupling from 2010 to 2012 and 2013 to 2015. (2) The decoupling states of Zhuolu, YangYuan, and Kangbao counties vary between strong, weak, and weak decoupling. Zhuolu, YangYuan, and Kangbao counties changed from strong to weak decoupling. Kangbao County was in expansive negative decoupling from 2006 to 2009 and strong decoupling from 2010 to 2015, while Zhuolu County was in strong decoupling from 2006 to 2009 and weak decoupling from 2010 to 2015. (3) Six districts, namely Yuxian, Qiaodong, Qiaoxi, Xuanhua, Xiahuayuan, and Chongli, showed strong decoupling and weak decoupling from 2006 to 2012, and recessive decoupling and strong negative decoupling from 2013 to 2015. Specifically, after two strong decouplings, Xuanhua District experienced a strong negative decoupling from 2013 to 2015, showing an increase in the ecological footprint of water resources but a regression in socioeconomics, which is the worst of all decouplings. Weak decoupling and strong decoupling are consistent, with weak decoupling and strong decoupling followed by a ‘Recessive’ state from 2013 to 2015. The recessive decoupling shows that the ecological footprint of water resources decreases at a faster rate than socioeconomic decline. Recessive coupling means that the ecological footprint of water resources is decreasing at a rate approximately equal to the rate of socioeconomic decline. Qiaodong and Qiaoxi Districts have undergone strong decoupling–expansive negative decoupling–strong decoupling, and the decoupling state was worse from 2010 to 2012, showing that the ecological footprint of water resources is increasing faster than the socioeconomic increase. The ecological footprint of water resources is increasing faster than the socioeconomic growth rate, which is a rough development mode of exchanging resources for development.

Comparing the four factors, in order of the contribution of the water-saving effect: technology effect > structure effect > population effect > economic effect. The total effect of the water resource ecological footprint in Zhangjiakou from 2006 to 2015 showed a negative value, as the inhibiting effect of the technological and structural effects on the increase in the water resource ecological footprint was greater than the contributing effect of the economic and population effects.

Table 3 shows the results of the correlation analysis of the specific factors influencing the water resource ecological footprint and technology efficiency effects in each district and county of Zhangjiakou during the study period: the total power of agricultural machinery, agricultural water pumps, water-saving irrigation machinery, number of electromechanical wells at the end of the year, the total number of industrialized operations, industrialization rate, and number of tourist arrivals in the city had a significant negative correlation with the water resource ecological footprint and contributed to the reduction of the water resource ecological footprint. The light industry and machinery are positively correlated with the water resource ecological footprint, while tobacco and textiles are significantly positively correlated with the water resource ecological footprint, indicating that the light industry, machinery, tobacco, and textile sectors have a dampening effect on the reduction of the water resource ecological footprint in Zhangjiakou.

As shown in Table 4, the water resource ecological footprints in Shangyi County and Chongli District showed a significant negative correlation with the number of tourists, agricultural water pumps, water-saving irrigation machinery, and year-end electromechanical wells. The water resource ecological footprint in the Qiaodong District showed a significant positive correlation with agricultural water pumps.

In summary, analysing the trends of different indicators for agriculture, industry, and services, and incorporating the decoupling of the water resources ecological footprint from the economy in Zhangjiakou. Calculating and identifying the key factors affecting the ecological footprint of water resources and the economy in Zhangjiakou. The results show that the total power of agricultural machinery, agricultural water pumps, water-saving irrigation machinery, number of electromechanical wells at the end of the year, total industrialized operations, industrialization rate, and number of urban tourists are significantly negatively correlated with the water resources ecological footprint. The total power of agricultural machinery and water-saving irrigation machinery have a linear regression relationship with the water resources ecological footprint, and this equation is water resource ecological footprint = −0.003 water-saving irrigation machinery −0.132 total power of agricultural machinery +221.79.

This paper aims to address the constraints of water scarcity on economic development, and finds that Zhangjiakou as a whole is strongly decoupled most of the time. The technology effect is the main factor that reduces the ecological footprint of water resources, and also is a key factor influencing the decoupling of the ecological footprint of water resources and economic growth in Zhangjiakou. The relationship between the total power of agricultural machinery, water-saving irrigation machinery, and the ecological footprint of water resources is linear. With the increase in the quantity of water-saving irrigation machinery and the total power of agricultural machinery, the ecological footprint of water resources decreased significantly.

Chang used the Tapio model to examine the performance of water utilization in 30 provinces of China. The result shows that the Northeastern provinces have largely increased the efficiency but the southwestern provinces have the efficiency declined (Chang & Zhu 2021). In regions such as Northwest China and along the Great Wall, machinery density is significantly negatively correlated with agroecological efficiency, while in Northeast China, machinery density is positively correlated with agroecological efficiency. Considering the characteristics of agricultural production in China and referring to previous research results, it illustrates that there is significant regional heterogeneity in the drivers of the evolution of agroecological efficiency in China. It is suggested that the Northwest and Great Wall regions should continue to strengthen agricultural infrastructure, improve agricultural water supply and drainage systems, and increase agricultural mechanization in the Northeast (Wang & Lin 2021). Also strengthening urban infrastructure can help improve regional economic development (Junaidi et al. 2022). The development of agricultural machinery and water-saving technology is the main method to improve agricultural water efficiency. Using agricultural machinery such as staggered vibratory subsoilers can loosen the soil, increase rainwater infiltration rates, and reduce runoff and water evaporation losses (Wang et al. 2019). Fang et al. (2017) applied the principal component analysis method to study irrigation water efficiency in different provinces of China, which showed that sophisticated irrigation management and water conservation measures influence irrigation water efficiency in highly developed agricultural provinces, making those factors strongly positive drivers. However, changes in irrigation water efficiency are mainly driven by economic development and structural adjustment in highly industrialized provinces, weakening those drivers. Zhai et al. (2021) conducted field trials from 2012 to 2015 and found that three 90 mm micro-sprinklers and four 120 mm water micro-sprinklers increased water use efficiency by 22.5 and 16.2%, respectively, compared to traditional flood irrigation. Solgi et al. (2022) in Iran used the AquaCrop model to study the effect of different surface deficit irrigation strategies on water use efficiency and wheat yield under five different climate scenarios. When irrigation water was reduced by 30%, agricultural water productivity (WP) increased by 0–18% during different growing seasons. Furthermore, sprinkler irrigation increased agricultural WP and maintained yields only in normal and wet years. Otherwise, sprinkler irrigation reduces agricultural WP and increases the pressure on the water sources. Therefore, synchronizing irrigation strategies with rainfall characteristics in areas with erratic rainfall will increase WP and maintain crop production. The Israeli government has invested heavily in research and development to make its agricultural water-saving irrigation technology and equipment superior while optimizing water allocation techniques and emphasizing agronomic and biological water-saving techniques (Trifonov et al. 2017).

This study uses LMDI and mathematical statistical analysis to find that the increase in water-saving irrigation machinery and the total power of farm machinery in Zhangjiakou led to a decrease in agricultural water use, similar to the results of Wang & Lin (2021). It could be that with the implementation of water conservation policies and the mechanization of agriculture to achieve large-scale agricultural operations, water-saving irrigation techniques are applied and popularized, increasing agricultural production while reducing the amount of water used for irrigation. By referring to the development experience of Israel, it is also important to focus on agronomic research and the development of more advanced water-saving techniques when increasing the number of water-saving irrigation machinery and the total power of agricultural machinery parameters.

To address water scarcity constraints on economic development. This study focuses on the decoupling relationship between water resources and economic development and its impact mechanisms in Zhangjiakou City. The analysis led to the following conclusions:

1. The water resources ecological footprint in Zhangjiakou showed a significant decreasing trend, and there are obvious spatial differences in both the water resources ecological footprint and the economy. The agricultural ecological footprint was dominant in all districts and counties (77.54 ± 14.35%). The ecological footprint of water resources decreased by 17.31% from 2006 to 2015, Xuanhua District has the largest average annual water resources ecological footprint, while Xiahuayuan District has the smallest. Zhangjiakou's GDP showed a significant increasing trend (an increase of 1.32 times). Significant spatial variation in GDP. Most districts and counties were dominated by the tertiary sector, with the exception of Guyuan, Kangbao, Shangyi and Xuanhua, Qiaodong, and Chongli Districts. Meanwhile, the Xuanhua District had the largest average annual GDP and the Xiahuayuan District was the smallest.

2. There was a strong decoupling between the ecological footprint of water resources and economic growth in Zhangjiakou between 2006 and 2015, and the decoupling status of different districts and counties was significantly different during the study period. This indicates that economic growth and water resource utilization coordinate development in most districts and counties, and water shortage is no longer a constraint to economic growth. Zhangbei, Shangyi, Huailai, Chicheng, and Wanquan Districts were strongly decoupled. Yu County, and Qiaodong, Qiaoxi, Xuanhua, Xiahuayuan, and Chongli Districts have a trend towards worse decoupling. There was strong and weak decoupling from 2006 to 2012, but the decoupling status declined from 2013 to 2015 with recessive decoupling and strong negative decoupling.

3. The technology effect, which is always negative, was the key factor affecting the decoupling of the water resources ecological footprint and economic growth in Zhangjiakou, with the number of water-saving irrigation machines and the total power of agricultural machinery being the most critical influencing factors. Ranked by the contribution rate of reducing the ecological footprint of water resources: technology effect > structure effect > population effect > economic scale effect. According to the correlation analysis and multiple regression analysis, there exists a linear regression equation which is water resource ecological footprint = −0.003 water-saving irrigation machinery −0.132 total power of agricultural machinery +221.79.

Therefore, for water-scarce cities such as Zhangjiakou, which are predominantly agricultural, it is important to adjust the structure of water use, focus on agronomic research, and develop more advanced water-saving technologies. Specifically, agricultural machinery and water-saving irrigation machinery can be increased, which will effectively reduce water consumption. At the same time, the government should promote agricultural mechanization and large-scale farming, which will effectively alleviate the problem of water scarcity limiting economic development.

This research was funded by China Three Gorges Corporation (grant number HB/ZB2021156) and the National Science and Technology Major Project of Water Pollution Control and Treatment (grant number 2017ZX07101003-008).

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.