Evaluation of water resources sustainable development in karst area based on the improved emergy ecological footprint model: A case study of Yunnan Province

The sustainable use of water resources is an important part of the construction of ecological civilization and is also the main content of the study of resources and environment (Oliveira 2017; Gleeson et al. 2020; Tian et al. 2021; Meng & Wang 2022). Sustainable development and utilization of water resources is an important prerequisite for regional economic development and is closely related to regional sustainable development, and has important strategic significance and special functions in the region (Chen et al. 2016; Larsen et al. 2016; Ali et al. 2019; Song et al. 2022). Behind the rapid economic development and population growth, the demand for water resources from industry and society has gradually increased (Flörke et al. 2018; Wang et al. 2021a; Darko et al. 2022; Mann & Gupta 2022). The uncontrolled abuse of water resources has caused ecological and environmental problems such as water depletion, water environment pollution, soil erosion, and water shortage (Liu et al. 2021; Michelle et al. 2021; Faye 2022; Hatami et al. 2022; Hojjati-Najafabadi et al. 2022; Karaman et al. 2022; Nguyen et al. 2022). The ‘2023 United Nations World Water Development Report’ jointly published by UNESCO and UN-Water pointed out that 2 billion people (approximately 25% of the world's population) currently lack access to safe drinking water, and 2–3 billion people experience water scarcity for at least one month each year. If international cooperation is not strengthened, the problem of water shortage will become more and more serious in the coming decades, with the global urban population facing water shortage expected to grow from 930 million in 2016 to 1.7 billion to 2.4 billion in 2050 (Liu 2023). The United Nations Water Conference 2023 adopted the ‘Water Action Agenda’. In the face of the increasingly severe water resources situation in the world, the participants discussed solutions and called for strengthened international cooperation to jointly promote the sustainable development of water resources (Li & Zheng 2023). China's per capita water resources are at a backward level in the world, making it one of the world's water-poor countries, and more than 60% of large- and medium-sized cities in China suffer from water shortage problems (Wang & Li 2021). With economic development and population growth, the demand for water resources and aquatic products is increasing and the discharge of wastewater is increasing, so the sustainable development of water resources is affected. How to improve the current situation of water resources, maintain the sustainable utilization of water resources, and ensure the sustainable development of water resources have become an important link to promote the coordinated development of population, resources, economy, and ecological environment.

The sustainable development of water resources is a current research hotspot (Ishaque et al. 2023; Islam et al. 2023; Mikulčić et al. 2023; Rahmani et al. 2023; Zhang et al. 2023). Many scholars have carried out research work on the sustainable development of water resources. Farrokhzadeh et al. (2020) used a multi-objective optimization model linked with the Water Evaluation and Planning (WEAP) software to optimize water allocation decisions over multiple years and make optimal planning in water resources necessary for sustainable socio-economic development in the Sistan region and its Hamoun wetland, located in southeast Iran. Ezzeldin et al. (2022) put forward a rainwater harvesting technique that combines geographic information systems (GIS), remote sensing (RS), multi-criteria analysis, and hydrological modeling in a case study in Wadi Watir in the Sinai Peninsula, Egypt. This research addresses the challenges of water scarcity along with socio-economic and environmental pressures while achieving sustainable development goals. Abedzadeh et al. (2020) used Fuzzy Fault Tree Analysis to assess risk-based assessment of water resources development plans (WRDPs) in Homozgan province in the South of Iran, under the sustainable development framework. The proposed approach not only addresses the risk of WRDPs in compliance with sustainable development objectives but also facilitates decision-making for risk management by prioritizing the factors in the failure of plans. Ifediegwu (2022) used an integrated method to assess the groundwater potential zones in the Lafia district utilizing RS, GIS, and the analytic hierarchy process (AHP). The results can aid sustainable groundwater resource management in this area. Shams & Muhammad (2022) proposed a novel framework for a critical assessment of the implementation of integrated water resources management and water–energy–food nexus in Afghanistan toward sustainable water resources management. The above-mentioned studies have carried out the sustainable development of water resources in different regions from different perspectives, and certain research results have been achieved. However, water resources not only have ecological attributes but also have socio-economic attributes. The evaluation of sustainable development of regional water resources is a composite system that organically combines socio-economic, resource, and environmental factors. The above methods cannot better reflect the complexity and comprehensiveness of the regional water resources sustainable development system.

The ecological footprint method proposed by Rees (1992) and Wackernagel et al. (1999) can make up for the shortcomings of the above methods. However, the information covered by the data accounts collected by the ecological footprint model of water resources is not comprehensive, and there is a lack of water pollutant accounts and aquatic product accounts. Most of the selected parameters are global equilibrium factors and yield factors, without considering regional and time differences, which can cause errors between the calculation results and the actual situation, and cannot accurately reflect the utilization of water resources in the region. In view of the above reasons, firstly, the water ecological footprint account is supplemented with a water pollution account and a water product account in addition to a water consumption account (including agricultural water account, industrial water account, domestic water account, and ecological environment water account), which further improves the water ecological footprint account and more accurately reflects the impact of regional water pollution on the ecosystem and the pressure of economic development on the ecosystem. Secondly, this paper improves it with the help of emergy theory (Odum 1996), converting different kinds of energy in each account into unified solar emergy through solar emergy transformity. After unification, various forms of energy can be quantitatively analyzed and studied, which truly reflects the relationship between the water environment and economic and social development. Then, in the emergy ecological footprint model of water resources, the emergy ecological footprint of water resources is calculated by using the regional emergy density of water resources in the current year, and the emergy ecological carrying capacity of water resources is calculated by using the regional average emergy density of water resources. The calculation results are more in line with the actual situation of regional water resources ecological sustainable development, and the evaluation results are more reasonable. The water ecological footprint assessment method based on the emergy theory has the characteristics of more scientific, perfect, operational, and practical value, and it comprehensively considers the influence of social and environmental factors. It is one of the most important ways to study the status of regional water resource utilization, judge the carrying capacity of water resources, and evaluate the sustainable development capacity of regional water resources.

This paper combines the emergy theory and water ecological footprint to take advantage of the strengths of these two theoretical models. The emergy ecological footprint model of water resources is composed of the emergy ecological footprint of water consumption, the emergy ecological footprint of water pollution, and the emergy ecological footprint of aquatic products. The emergy ecological carrying capacity of water resources is composed of surface water chemical energy, groundwater chemical energy, and rainwater potential energy. Then, according to the regional water resources' emergy ecological carrying capacity, emergy ecological footprint, and other related data, five water resources sustainable development evaluation indexes were calculated, namely emergy ecological deficit/surplus of per capita water resources, ecological pressure index of water resources, sustainable utilization index of water resources, eco-economic coordination index of water resources, and emergy ecological footprint of water resource of 10,000 Yuan GDP. The current situation of sustainable utilization of water resources in Yunnan Province from 2012 to 2021 was analyzed and evaluated, and the internal driving factors were analyzed from natural ecological factors and social factors, and the optimization paths of water resources sustainable development were proposed to improve the current situation. The research results can provide new ideas for the evaluation and analysis of sustainable development of water resources in the karst region, which is valuable for alleviating the contradiction between water supply and demand of water resources and promoting the sustainable development of regional society and economy and the virtuous cycle of water ecological environment.

Canadian ecological economist Rees (1992) pioneered the concept of ecological footprint and proposed the calculation method of the ecological footprint model in 1996 in collaboration with his doctoral student Wackernagel et al. (1999) to determine whether the area was sustainable by comparing regional ecological footprint and ecological carrying capacity. Odum (1996) proposed a new theory and method of emergy analysis, which can convert different types of energy into a unified unit of solar emergy through the solar emergy transformity, and then quantitatively analyze and study it to truly reflect the relationship between the ecological environment and economic and social development. Later, some scholars introduced the emergy theory into the ecological footprint model, and through continuous practice and application, it developed into a more systematic emergy ecological footprint model to determine the sustainable development of the region (Zadgaonkar & Mandavgane 2020; Liu et al. 2022). According to the above theory, this paper tried to combine the solar emergy in the emergy theory with the ecological carrying capacity and ecological footprint in the ecological footprint model to maximize the advantages of these two theoretical models. Ecosystems provide renewable and non-renewable resources. Non-renewable resources are gradually consumed, while renewable resources can be used continuously. Therefore, this paper selects water resources as the renewable resources of Yunnan Province in the study area. The emergy ecological carrying capacity indicators of water resources include surface water chemical energy, groundwater chemical energy, and rainwater potential energy. The emergy ecological footprint indicators of water resources include water consumption account, water pollutant account, and aquatic product account. Meanwhile, with the solar emergy transformity as a parameter, different types of energy in each account can be converted into the same form of solar emergy. Combined with five evaluation indexes of sustainable development of water resources, the current situation of sustainable utilization of water resources in the region can be analyzed and evaluated, which will more accurately simulate the dynamic change trend of sustainable development of regional water resources.

Since there are differences among regions in terms of water resources, climate conditions, land area, population size, and economic level, it is not comprehensive enough to evaluate the sustainable development status of regions by only relying on two basic indicators (emergy ecological carrying capacity and emergy ecological footprint). In order to more objectively evaluate the regional sustainable development, on the basis of the original, five sustainable evaluation indicators (emergy ecological deficit/surplus of per capita water resources, ecological pressure index of water resources, sustainable utilization index of water resources, eco-economic coordination index of water resources, and emergy ecological footprint of water resource of 10,000 Yuan GDP) are comprehensively considered in order to make a more accurate evaluation of the ecological status of the region, so as to put forward more reasonable suggestions.

When Wec = Wef, the supply and demand of water resources are in balance, indicating that the emergy ecological carrying capacity of regional water resources can meet the demand of urban and rural residents for production and living water. When Wef < Wec, there is an ecological surplus of water resources, indicating that the regional water resources supply can meet the demand, which is conducive to the sustainable development of the region. When Wef > Wec, there is an ecological deficit of water resources, indicating that the regional socio-economic development exceeds its ecological load on water resource utilization, which is not conducive to the sustainable development of the region.

When WEPI is close to 1, it indicates that the regional water resources supply and consumption are basically equal and are in the critical state of sustainable development of water resources. When 0 < WEPI < 1, it indicates that the regional water resources supply can support its consumption status and level. When WEPI > 1, it indicates that the regional water resources are in an unsustainable state, and the larger the value, the greater the regional water resources' ecological pressure. At this time, measures should be taken to improve the water's ecological carrying capacity.

The value range of WECI is (1, 1.414). The closer the WECI is to 1, the worse the ecological and economic coordination of water resources; the closer the WECI is to 1.414, the better the ecological and economic coordination of water resources. When WECI = 1.414, it means that the water resources are in the best ecological and economic coordination state.

The distribution area of karst in the world is nearly 2.2 × 10⁷ km², and the karst area in China is 3.4 × 10⁶ km², accounting for about one-third of the land area, mostly distributed in the southern regions with a warm and humid climate, involving many provinces such as Sichuan, Chongqing, Hunan, Guangdong, Guizhou, Guangxi, and Yunnan. The southwestern karst area with Guizhou, Guangxi, and Yunnan as the main body is one of the largest contiguous exposed carbonate rock distribution areas in the world. The area of Yunnan Province is 3.941 × 10⁵ km², of which 1.1 × 10⁵ km² is covered by karst landforms, accounting for 28.15% of the total area. Counties with karst landform area, which accounts for over 30% of the total area, are called karst-developed counties, while counties with karst area accounting for over 70% of the total area are called severe karst counties. There are 116 karst-developed counties and 65 severe karst counties in Yunnan Province (Chang 2023).

This paper collates and collects relevant data on Yunnan Province from 2012 to 2021. The data on annual rainfall, agricultural water consumption, industrial water consumption, domestic water consumption, ecological and environmental water consumption, water consumption of 10,000 Yuan GDP, surface water resources, and underground water resources are obtained from ‘Yunnan Water Resources Bulletin’ (2012–2021), and the data of GDP, sewage discharge, aquatic products production, sewage discharge, aquatic products production, and year-end resident population are obtained from ‘Yunnan Statistical Yearbook’ (2013–2022). See Supplementary material for the specific collated categories.

As a renewable resource, water resources mainly come from rainwater, surface water, and groundwater. In 2012–2021, the fluctuation range of water resources emergy in Yunnan Province was 8.51 × 10²² ∼ 1.15 × 10²³ sej, and the emergy ecological carrying capacity of water resources showed a fluctuating upward trend, with an overall increase rate of about 2.08%. Among them, the emergy ecological carrying capacity of water resources was the highest in 2017, which was 1.80 × 10⁷ hm², corresponding to an average annual precipitation of 1,351.5 mm. The lowest value was 1.33 × 10⁷ hm² in 2019, corresponding to an average annual precipitation of 1,008 mm. The emergy ecological carrying capacity of rainwater was the main contributor to the emergy ecological carrying capacity of water resources, accounting for 81.36% on average. The emergy ecological carrying capacity of surface water was 1.83 × 10⁶ ∼ 2.63 × 10⁶ hm², accounting for 13.93% on average. The emergy ecological carrying capacity of groundwater was the smallest, and the annual variation range was not large. The average annual value was 7.44 × 10⁵ hm², accounting for 4.72% on average. The annual variation of the emergy ecological carrying capacity of water resources in Yunnan Province was closely related to the annual variation of the average annual precipitation. The emergy ecological carrying capacity of water resources increased with the increase of rainfall. It showed that the average annual precipitation in Yunnan Province played a decisive role in the emergy ecological carrying capacity of water resources. On the one hand, this reflects the weak self-regulation ability of water resources carrying capacity in Yunnan Province, which relies heavily on atmospheric precipitation. On the other hand, the intensity of human activities has increased with the continuous development of society, such as the rapid development of tourism, accelerated urbanization, and rapid economic development, which have caused excessive use of water resources and water pollution, resulting in the reduction of human available water resources and further affecting the emergy ecological carrying capacity of water resources.

During the study period, the emergy ecological footprint of water resources decreased from 1.72 × 10⁷ hm² to 1.68 × 10⁷ hm², with an overall decrease rate of about 2.31%. Among the ecological footprint accounts, the water consumption account had the greatest impact on the ecological footprint of water resources, with an average contribution rate of 59.59%. The aquatic product account and the water pollution account had a relatively small impact on the ecological footprint of water resources, with an average contribution rate of 20.29 and 20.12%, respectively. The water consumption account was divided into four types of water accounts: agricultural, industrial, domestic, and eco-environment. The agricultural water consumption account (WR1) accounted for 41.46%, the industrial water consumption account (WR2) accounted for 12.46%, the domestic water consumption account (WR3) accounted for 4.73%, and the ecological environment water consumption account (WR4) accounted for 0.94%. The emergy ecological footprint of agricultural water consumption accounted for the largest proportion, indicating that the water resources in Yunnan Province were mainly invested in agriculture, and the agricultural water use footprint showed a fluctuating upward trend in general, with an increased rate of 6.20%. The overall emergy ecological footprint of industrial water consumption showed a fluctuating downward trend, with a decline rate of 47.05%. The reason was that large enterprises or factories attach importance to the use of reused water and the recycling of recycled water, and the phenomenon of wasteful water resources was decreasing day by day. The overall emergy ecological footprint of domestic water consumption showed a fluctuating upward trend, with an increase rate of 50.79%. The reason for this was that the population in Yunnan Province is increasing, human activities need to consume a large amount of surface water or groundwater resources, and the domestic water consumption of residents has increased significantly. The emergy ecological footprint of ecological environment water consumption had the smallest proportion, but increased year by year, from 5.61 × 10⁴ hm² in 2012 to 2.67 × 10⁵ hm² in 2021. It reflected that Yunnan Province was striving to improve the urban and rural water ecological environment and green sustainable development. The emergy ecological footprint of water pollution increased from 3.25 × 10⁶ hm² in 2012 to 3.39 × 10⁶ hm² in 2021, with a growth rate of 4.03%, indicating that the discharge of wastewater in Yunnan Province showed an increasing trend, and water pollution management should be paid high attention. The emergy ecological footprint of aquatic products showed a fluctuating upward trend, with an increase rate of 4.96%. This was mainly due to the increase in regional population and the demand for aquatic products.

From 2012 to 2021, the sustainable utilization index of water resources increased in fluctuation, and the change trend was negatively correlated with the trend of the ecological pressure index of water resources. The water resources in 2016, 2017, 2018, and 2020 were in surplus and weakly sustainable utilization. The ecological pressure index of water resources was 0.9164, 0.7837, 0.7946, and 0.9764, respectively. The sustainable utilization index of water resources was 0.0836, 0.2163, 0.2054, and 0.0236, respectively, indicating that the regional water resources supply in that year can support its consumption status and level, and the emergy ecological carrying capacity of water resources can support the future emergy ecological footprint of water resource growth, and there is no damage to the ability to sustain water resources use in the future. For the rest of the years, the water resources were in an unsustainable state of utilization, and the water resources used were in a dangerous state of ecological deficit. The ecological pressure index of water resources was greater than 1, indicating that the emergy ecological carrying capacity of water resources in that year was not enough to support the emergy ecological footprint of water resources, which has caused damage to the ability to continuously utilize water resources in the future. Among them, 2019 was the year with the largest deficit, with a value of − 0.1201, and it was also the year with the lowest sustainable utilization index, with a value of −0.4387. Because the annual average rainfall in this year was the smallest, the total amount of water resources was significantly smaller than in other years, and the emergy ecological carrying capacity of water resources decreased, but the emergy ecological footprint of water resources was the largest, leading to an increase in ecological pressure on the water resource. As a side reflection of the ecological pressure index of water resources, the sustainable utilization index of water resources and the emergy ecological carrying capacity of water resources are affected by the average annual rainfall. If the average annual rainfall becomes smaller, there may be a water ecological deficit or a low ecological surplus of water resources, which will lead to an increase in the ecological pressure of water resources, thus affecting the sustainable use of water resources in the future.

The eco-economic coordination index of water resources showed a fluctuating up-and-down trend. The fluctuation range of WECI was 1.392–1.414, and the multi-year average was 1.409, which indicated that the coordination between the water resources ecosystem and the socio-economic system was relatively stable. The WECI values for 2013, 2015, and 2020 were 1.414, indicating that the water resources were in the best ecological and economic coordination. The year 2019 had the lowest value of 1.392, which meant that the ecological and economic coordination of water resources was relatively poor. Due to the industrial restructuring and technological progress in Yunnan Province in recent years, the utilization efficiency of water resources has been improved. However, it is still necessary to pay attention to the sustainable utilization state of water resources, improve the ecological and social coordination level of water resources, and avoid the decline of the ecological coordination index.

The emergy ecological footprint of water resources of 10,000 Yuan GDP showed a decreasing trend, from 0.1528 hm²/10,000 Yuan in 2012 to 0.0587 hm²/10,000 Yuan in 2021, with a decrease of about 61.60%. The reason for the decline was that, on the one hand, the GDP of Yunnan Province has been increasing year by year with rapid economic development, rising from 1.03 × 10⁸ million Yuan in 2012 to 2.71 × 10⁸ million Yuan in 2021. On the other hand, with technological progress, the water consumption per 10,000 Yuan of GDP has decreased year by year, from 144 m³/10,000 Yuan in 2012 to 59 m³/10,000 Yuan in 2021. During the period from 2012 to 2019, the emergy ecological footprint of water resources of 10,000 Yuan GDP decreased rapidly. Because of the rapid economic development and population growth in Yunnan Province, the demand for water consumption in each account increased. The stable stage from 2020 to 2021 was due to the progress of science and technology, the efficiency of water resources development and utilization was improved, resulting in a decrease in water consumption per 10,000 Yuan of added value produced. It also benefits from the government's development of a green economy and people's increased awareness of water conservation, thus improving the efficiency of water resources development and utilization. From the side, it reflects that water resources are constrained by internal factors and have limited space for sustainable utilization.

Through the analysis of the current situation of sustainable development of water resources in Yunnan Province during the study period, it can be seen that water resources are generally in an ecological deficit and unsustainable utilization state. However, the changing trend of the comprehensive evaluation index of water resources sustainability shows that the sustainability of water resources is constrained by rainfall and internal factors, and the future ecological carrying capacity of water resources may not be able to support the social development needs. Therefore, this paper analyzes the internal driving factors of sustainable development of water resources from two aspects, namely natural ecological factors and social factors, and puts forward relevant optimization paths.

Natural ecology mainly affects the sustainability of water resources in three main ways. From the perspective of natural geographical conditions, Yunnan is a mountainous province, which belongs to the mountainous plateau terrain. The landform is complex and diverse. The terrain is characterized by high peaks in the north and low peaks in the south, ranging from the highest point of 6,740 m, the main peak of Meili Snow Mountain, Kawagbo Peak, fell to the lowest point of 76.4 m in Hekou County, showing its significant changes in height. The transition from plateau to mountain gradually becomes gentle, the river valleys are deeply embedded under the plateau surface and developed, and the basins are intertwined and coexist among the mountains, which together constitute a complex and diverse landform. On the one hand, the high mountains and steep gorges are deep, the construction of reservoirs is extremely difficult, and the development and utilization of water resources is difficult, resulting in engineering water shortage. On the other hand, under the effect of gravity, the soil matrix of the mountain system loses a lot, the soil water content decreases rapidly, and the ecological environment is extremely fragile, which affects the carrying capacity of water resources. From the perspective of geological structure conditions, karst vulnerability in karst areas consists of mountain system vulnerability and topographic vulnerability. Due to the extremely rapid loss of surface water in karst areas, it is easy to cause frequent flooding and drought disasters in karst mountainous areas, resulting in seasonal water shortages. Therefore, the unique geological structure also affects the sustainable development of water resources.

From the perspective of the hydrological system, Yunnan Province is a typical karst mountainous terrain, which has a dual hydrogeological structure of surface and underground due to special geological and climatic conditions. Surface water infiltration is severe, making it difficult to form a sustainable water surface and having poor water storage capacity. Yunnan has a large difference in terrain height, which makes the exploitation of surface water resources difficult, and the underground water is deeply buried and extremely unevenly distributed in space. This is an important reason for the difficulty of obtaining water and surface drought in karst mountains. In summary, natural ecology mainly controls the sustainable development of water resources by affecting the strength of water resources carrying capacity.

The influence of social factors is mainly reflected in increasing the ecological footprint of water resources, reducing the ecological carrying capacity of water resources during the study period, leading to the decrease of water resources' ecological surplus and the increase of water resources' ecological pressure. Firstly, from 2012 to 2021, Yunnan Province was in a period of rapid urbanization, with the population increasing from 46.59 million to 46.9 million, and GDP increasing from 1,030.947 billion to 2,714.676 billion. The demand for water for living and ecological environment is constantly increasing, and the water consumption of agriculture, aquatic products, and wastewater discharge has been at a high level. Secondly, in terms of land development and utilization, Yunnan Province is located in the karst mountainous area, and the increase in population makes the phenomenon of sloping land reclamation very common, which leads to long-term indiscriminate logging and soil erosion, and the water ecological environment is deteriorating, resulting in the decrease of water resources carrying capacity.

In order to guarantee the sustainable development of water resources in Yunnan Province, based on the analysis of the driving factors and the current situation of water resources development and utilization, the following optimization paths are proposed:

• (1)

  Strengthen policy guidance, change the development concept, and improve water resource development and utilization efficiency

The emergy ecological footprint of water resources increases with socio-economic development, and economic and population growth will definitely consume a large amount of water resources and water products. A good economic development model can improve the efficiency of water resource utilization, reduce water losses, and alleviate the ecological pressure on water resources. Yunnan Province should adhere to the policy of ‘ecological priority and green development’, improve agricultural irrigation technology to reduce agricultural water use, improve wastewater treatment technology to reduce wastewater discharge; reduce the input of water resources in aquatic products production; and improve the recycling rate of water resources to form a sustainable development model of water resources.

• (2)

  Adjust the supply and demand structure of water resources, optimize the allocation of water resources, and develop a green low-carbon economy

The amount of industrial water and industrial sewage discharge plays an important role in the emergy ecological footprint of water resources. The government should adjust the structure of water resources supply and demand at the macro level, and optimize the allocation of water resources in time and space. Developing low-water consumption industries will help economic growth, upgrading or eliminating high-water consumption industries, adjusting and optimizing industrial structure, and forming a green carbon circular economy model. Through the development and utilization of surface water and groundwater, high-quality development of water conservancy projects to regulate the supply of water resources. At the same time, we should further promote the concept of water saving, implement step water price, improve the consumption structure of water resources, improve the utilization efficiency of water resources, and ensure the sustainable development of urban water resources.

• (3)

  Prevention and control of water pollution, protection of the ecological environment, and improvement of the water resources systems and policies

Government departments should speed up the establishment and improvement of urban and rural sewage and enterprise sewage treatment project implementation progress, and effectively improve the water environment, to solve the enterprise excessive discharge of sewage and urban and rural domestic sewage excessive discharge, establish and improve the accountability system for water pollution incidents, and resolutely close down enterprises or production lines that seriously exceed the discharge standards. The environmental protection department should establish and improve the legal system of water resources protection, strengthen the comprehensive management of water areas, increase the efforts of pollution control and water environmental protection of important water areas, and protect the good state of surface water and groundwater quality such as rivers, lakes, and reservoirs. We should take the biological-ecological pollution control development path, improve the water environment, and improve the ecological environment of water resources' self-cleaning and repair capabilities.

Through a series of measures and policies, we can improve the ecological environment of water resources, enhance the restoration capacity and cleaning capacity of water resources' ecological environment, and accelerate the formation of a green development pattern that matches the ecological footprint of water resources' energy value with the ecological carrying capacity of water resources, and form a situation of harmonious coexistence between human and nature.

Water resources in Yunnan Province were generally in an ecological deficit and unsustainable utilization state during the study period. 2019 was the year with the largest deficit with its value of −0.1201 hm²/cap; 2019 was the year with the highest ecological pressure index of water resources with its value of 1.4387; 2019 was the year with the lowest sustainable utilization index of water resources with its value of −0.4387. In 2019, the emergy ecological carrying capacity of water resources was the lowest, the emergy ecological footprint of water resources was the highest, and the corresponding average annual rainfall was the smallest, with a value of 1,008 mm. During the study period, the ecological pressure index of water resources was relatively high, and the sustainable utilization index of water resources was relatively low. The emergy ecological carrying capacity of water resources was not enough to support the emergy ecological footprint of water resources, which has damaged the ability of sustainable utilization of water resources in the future, and the water resources were in an unsustainable state. Natural ecological factors control the level of sustainable development of water resources mainly by influencing the intensity of the carrying capacity of water resources. The influence of social factors is mainly reflected in the increase of the emergy ecological footprint of water resources in Yunnan Province during the study period, which reduces the emergy ecological carrying capacity of water resources, leading to the decrease of water resources ecological surplus and the increase of water resources ecological pressure. The sustainability of water resources is constrained by rainfall and internal factors, and the future ecological carrying capacity of water resources may not be able to support the social development needs.

During the research period, the emergy ecological carrying capacity of water resources showed a fluctuating increase, with an overall increase rate of approximately 2.08%. Overall, it was still at a relatively low level. The emergy ecological carrying capacity of rainwater was the main contributor to the emergy ecological carrying capacity of water resources, accounting for 81.36% on average. The emergy ecological carrying capacity of surface water and the emergy ecological carrying capacity of groundwater accounted for 13.93 and 4.72%, respectively. The annual change pattern of the emergy ecological carrying capacity of water resources in Yunnan Province is positively correlated with the annual change pattern of the average annual rainfall. The emergy ecological footprint of water resources decreased from 1.72 × 10⁷ to 1.68 × 10⁷ hm² during the study period, with an overall decrease rate of about 2.31%. Among the ecological footprint accounts, the water consumption account had the greatest impact on the emergy ecological footprint of water resources, with an average contribution rate of 59.59%. The aquatic products account and the water pollution account had relatively small impacts on the emergy ecological footprint of water resources, with average contribution rates of 20.29 and 20.12%, respectively. However, the emergy ecological footprint of water pollution and the emergy ecological footprint of aquatic products showed an upward change, with an upward rate of 4.03 and 4.96%, respectively. During the study period, the emergy ecological carrying capacity of water resources showed an upward trend, the emergy ecological footprint of water resources emergy showed a downward trend, the ecological pressure index of water resources decreased in fluctuation, the sustainable utilization index of water resources increased in fluctuation, and the water resources showed a sustainable development trend. The emergy ecological footprint of water resources of 10,000 Yuan GDP decreased from 0.1528 hm^2/10,000 Yuan in 2012 to 0.0587 hm^2/10,000 Yuan in 2021, with a decrease of about 61.60%. The efficiency of water resources development and utilization has improved. The eco-economic coordination index of water resources ranged from 1.392 to 1.414, with a multi-year average of 1.409, indicating that the coordination of water resources ecosystem and socio-economic system was relatively stable. In recent years, industrial structure adjustment and scientific and technological progress have continuously improved the utilization efficiency of water resources, and water resources have shown a sustainable development trend.

The sustainable development of water resources is influenced by both natural ecological factors and social factors. The natural ecological factors are mainly manifested as serious soil erosion caused by the fragility of the ecological environment in karst mountainous areas, and the highly permeable hydrogeological structure resulting in weak surface water storage capacity and lack of surface water, thus affecting the level of the ecological carrying capacity of the regional water resources. The social factors are mainly manifested by the increase in demand for water products due to the increase in population and the increase in demand for water resources due to the rapid economic development, as well as the deterioration of the water environment due to the overload discharge of wastewater, which makes the ecological footprint of water resources increase and the ecological carrying capacity of water resources decrease. The optimal path for sustainable development of water resources mainly includes strengthening policy guidance, changing development concepts, improving water resources development and utilization rate; adjusting water resources supply and demand structure, optimizing water resources allocation; developing a green low-carbon economy; preventing and control water pollution, protect ecological environment, and improve water resources system policy.

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

The authors declare there is no conflict.