The study of water security evaluation indices under climate change impact

With the rapid development of global climate change and urbanization and the rapid development of economic construction, the demand for water resource development and utilization has greatly increased. Since the 1980s, global freshwater use has continued to grow at a rate of about 1% annually, but there are still more than 1 billion people with insufficient water (UNESCO 2021). Climate change is one of the most pressing global challenges, with profound impacts on natural and human systems. Among the various sectors affected by climate change, water resources are particularly vulnerable. The availability, quality, and distribution of water resources are critical for ecosystem health, human survival, agriculture, industry, and energy production. Therefore, understanding and assessing the impacts of climate change on water security is essential for developing adaptive strategies to ensure sustainable water management. The traditional water security studies under climate change impact mainly include the following aspects: ① Watershed water balance (Cramer et al. 2018; Alimohammadi et al. 2020; Fiorillo et al. 2021; Ranjan & Mishra 2023). ② Regional available water supply and water demand (Gorguner & Kavvas 2020; Huang et al. 2020; Granados et al. 2021; Gomez-Gomez et al. 2022). ③ Flood and drought frequency (Iglesias et al. 2012; Her et al. 2019; Suman & Maity 2021). ④ Agricultural irrigation water supply (Joseph et al. 2018; Jose & Dwarakish 2020; Sun et al. 2021). ⑤ Water supply system reliability, resilience, and vulnerability (Lespinas et al. 2014; Van Vuuren et al. 2014; Lehner et al. 2020). ⑥ Water quality (Marx et al. 2018; Ortiz-Bobea et al. 2021). Noto et al. (2023) carried out climate change in the Mediterranean Basin (Part II), in which an overview of recent works relevant to climate change indicators in the Mediterranean basin was put forward, mainly focusing on the last ten years of research. Pastén-Zapata et al. (2022) put forward a more robust evaluation of the climate model and hydrological impact uncertainties. Pourmokhtarian et al. (2016) studied the effects of the climate downscaling technique and observational dataset on modeled ecological responses. Schilling et al. (2020) analyzed Climate change vulnerability, water resources, and social implications in North Africa. Smid & Costa (2018) proposed climate projections and downscaling techniques. Stephens et al. (2018) studied the implications of future climate change for event-based hydrologic models. Yao et al. (2020) studied the identification of regional water security issues in China, using a novel water security comprehensive evaluation model. In his study, the flood control security index, resource security index, and ecological security index were proposed according to the construction principle of the human development index. Xiao et al. (2008) studied the comprehensive assessment of water security for inland watersheds in the Hexi Corridor, Northwest China, in which, the water resource security of three watersheds in the Hexi Corridor (Northwest China) was assessed using a multi-level, multi-target analytical hierarchy process approach.

Since the 21st century, the climate change impact on water security has gradually become a research hot spot in the field of water resources, attracting the attention of various governments and non-governmental organizations, including the United Nations, the World Bank, and the Asian Development Bank (Cook & Bakke 2012; Gerlak & Mukhtarov 2015). On World Water Day 2013, the United Nations Water Organization released a Water Security Analysis Summary, in which the possibility of putting a water-related sustainable development objective into the United Nations Sustainable Development Goal was discussed (UN Water 2013). Water security issues under climate change impact would also have a profound impact on national security. Water security, as a key goal for governments and non-governmental institutions in management sectors, can reduce political conflict risk and promote sustainable development, which has been included in the global political agenda and won the high-level attention of various countries (Kelly 2009).

However, in the previous studies, the number of quantitative indices is limited. Most indices cannot be characterized by quantitative data. Some indices cannot be obtained from public sources, and the data quality and consistency cannot be guaranteed, which results in problems such as incomplete evaluation results, incomparable evaluation results between different years and regions. Moreover, the existing research reports and literature are short of classification indices for adaptation to climate change impact. Therefore, in order to fully understand the potential threat and actual climate change impact on water security, it is necessary to establish a set of indices that can integrate climate change adaptation works and professional evaluation indices.

Water security refers to the availability of sufficient and safe water to sustain livelihoods, human health, economic development, and ecosystem integrity. Generally speaking, it encompasses four main dimensions: availability, accessibility, utilization, and sustainability. Given the complexity of these dimensions and their interdependencies, it is crucial to develop comprehensive evaluation indices that can effectively monitor and assess the state of water security under changing climatic conditions. Therefore, the main study objectives and contents in this paper include: ① The definition, connotation, and evaluation dimensions of water security under climate change impact, as well as relevant data acquisition or application methods, are studied. ② Through investigation and analysis, the national adaptation to climate change indices is proposed. ③ Considering the discipline background of water security under climate change impact, a series of water security evaluation indices that include quantity adequacy, water quality suitability, sustainability, cost affordability, and flood control guarantee are constructed. ④ The weights of water security evaluation indices are quantified using the experts' decision-making, cluster, and hierarchical analysis methods. ⑤ The regional water security evaluation indices are applied to water security evaluation in the provinces (regions) of China, and the water security classification and grades in China under the climate change impact are obtained.

Water security under climate change impact is a composite concept system, which involves a multidisciplinary background. It is a systematic judgement of the overall situation of the water system from the comprehensive perspective of water resource utilization, ecological environment protection, and disaster prevention (Gerlak et al. 2018). According to the definition of water security issued by international authoritative organizations (Table 1), in this paper, water security under climate change impact is defined as follows: ① to cope with the future climate change impact; ② to sustainably supply sufficient water; ③ to guarantee standard quality water and cost-affordable water and to ensure the needs of human life; ④ to meet the requirement of social economy and ecological health; and ⑤ to reduce flood hazards and droughts.

Water resource security is a core content of water security. Considering water resources security, the essence of water security under climate change impact is whether the water resource quantity supply can meet the various reasonable water demands. Considering the water needs of living and production, water security under climate change impact should meet all household water use and sanitation requirements and ensure that everyone has the right to get secure drinking water. At the same time, the steady development of agriculture, industry, and energy economies should be guaranteed. Considering ecological water demand, water security under climate change should ensure the minimum water demand of the ecosystem, and human beings should not occupy too much ecological water to worsen the ecosystem.

Water resource quantity guarantee is the primary factor to measure water security under climate change impact. It was very often that the regional water resources evaluation took the per capita average water resource index to reflect the status of regional water resources, without considering the difficulty of water resource exploitation, water quality, and ecological water demand, which cannot truly reflect the available water resource in this region. Concerning water security, it is impossible to measure whether the water resources in this region can meet the needs of all parties.

In addition to ensuring a sufficient and stable water supply at the present stage, the water supply and demand should also consider the long-term water security under the climate change impact and meet the long-term needs of human society, economy, and ecology, i.e. sustainability guarantee. When explaining the concept of water security, some international organizations consider sustainability as an indispensable key connotation to measure water security (Xiao et al. 2008). In previous studies, few works took sustainability as a separate evaluation dimension; in most cases, the sustainability concept was dispersed in the water resources, ecological environment, or other dimensions. The sustainability connotation for water security under climate change impact should include the long-term guarantee of water resource endowment, development and utilization, and ecological water demand. They are closely related and mutually influenced. Therefore, it is the best way to take sustainability as an independent evaluation dimension.

Water resource quality guarantee is that water quality should meet the quality requirements of ecology, life, and production water use. The ecological water use quality guarantee, namely the water environment security, should focus on the key natural water quality problems (Kimy & Park 2018). Generally, the selected indices for water environment evaluation are easily overlapped. If we put all of the unscreened indices into the evaluation index system without screening, it is easy to result in index redundancy, and the relevant indices would be repeated. In order to guarantee life and production water quality, we should evaluate the water quality at the end of the pipe networks.

• Economic security. Economic security emphasizes that water resources can ensure the economy's smooth operation. The local competitive industries should not lose their market competitiveness because of unreasonable water prices. For enterprises, it is necessary to pay special attention to the local economic structure and development degree to avoid excessive water expenditure and ensure the local enterprise's steady development. For individuals, water security under climate change impact refers to the ability to obtain affordable water to meet drinking, washing, and livelihood needs (Holding & Allen 2016). Water security under climate change impacts emphasizes that domestic water use is a basic human right. The water cost affordability is the key to affecting whether the water users can obtain sufficient water, especially in areas with low economic development levels and low per capita income. Some researchers considered the economic security evaluation content, they put the indices, such as gross domestic product (GDP), social, and economic data indices or industrial water consumption's added value index, into the water security evaluation, but such kinds of indices are not closely related to water resources, it really does not reflect the real connotation of economic security in water security evaluation, but it reduces the sensitivity of water security diagnosis.

• Flood disaster prevention. Flood disaster prevention under climate change impact is related to social stability, economic development, and the safety of people's lives and property, which is an important connotation of water security. Most studies consider flood and drought disasters and affordability as one dimension in evaluating water security and neglect the duplication between them (Octavianti & Staddon 2021). Flood and drought disasters contain the connotation of water resource quantity. It is an important index to measure the satisfaction degree of different water use sectors.

• Grain security. Some studies take grain security as a dimension of water security evaluation and put indices such as grain output into the water security evaluation (Falkenmark 1992). It is necessary to consider water security from the standpoint of grain security. But it should be integrated into water resources. Grain security evaluation should start from the supporting role of water to grain, that is, whether agricultural water supply meets the demand of agricultural water use, rather than directly integrating grain output into the water security evaluation under climate change impact.

Considering that climate change's impact on water security has both strong professional and policy aspects, this study establishes a set of indices to assess water security under the impact of climate change, including both the national policy level and the professional technical level.

In order to objectively conduct comprehensive statistics, assessment, monitoring, and evaluation of the progress of national adaptation to climate change, this study constructed a set of national indices for climate change, including nine first-level indices and 36 second-level indices; see Table 2.

The criterion layer includes quantity adequacy, water quality suitability, sustainability, cost affordability, flood control security, reliability criteria. Water security evaluation involves different scales, such as macro-, medium-, and micro-scale. Taking into account the available data acquisition and an appropriate regional scale, the water security evaluation indices under the impact of climate change were established by investigation and by referencing the previous research findings; see Table 3.

In Table 3, ① the numbers in the brackets are the index weights; ② the rural drinking water safety standard is a comprehensive index reflecting water quantity, water quality, and convenience. In order to avoid repetition among the indices, the water quality suitability no longer includes the rural drinking water index; ③ according to expert consultation, there are obvious differences in the surface water and groundwater water supply in different regions, and subjective empowerment is not appropriate. The proportion of surface water and groundwater in different regions was chosen as the objective weight.

The above-studied indices effectively incorporate the notion of water security and its associated fields within the context of climate change impacts, thereby enhancing the scientific validity and rationality of water security assessments to some extent.

The expert decision-making method (Octavianti & Staddon 2021) is to gather experts to carry out decision-making, quantify decision results, and make consistency tests using mathematical-statistical methods.

The Cluster analysis method is an ideal multivariate statistical technique, mainly including the hierarchical clustering method and the iterative clustering method.

In this paper, the conjunctive use of the expert decision-making method and the hierarchical clustering method was adopted to determine the index weights and to standardize the threshold for the indices.

• (1) Index weight quantification. The cluster hierarchical analysis method was used to construct the pairwise discriminant matrix between various dimensions and indices. Two rounds of index formulation and weight scoring and questionnaire consultation were conducted with 28 authoritative experts in global water security research and management departments. According to the first round of expert consultation opinions, the evaluation indices were adjusted and then the revised scoring and data analysis results were returned to the relevant experts and a second round of scoring was carried out. Based on the experts' quantitative scores for the criterion layers, sub-criterion layers, and different indices, the weight coefficients of the indices were calculated using the discrimination matrix. Then, the non-parametric test method – Kendall coordination coefficient (W) was used to test the consistency of the results, in which, w = 0.583 and significance level P = 0. The significance test shows that the experts’ decision-making results have good consistency and the indices weights are relatively reliable (Table 4).

• (2) Data timescale and normalization. There are differences in the attributes of water security evaluation indices under climate change impact. The evaluation for a certain year may be unreasonable. It is necessary to analyze and judge the characterization ability of the evaluation indices according to the time scale.

• • ① Present status indices. These kinds of indices are affected by national construction, management, and other measures. The data in the latest year were used to characterize the current situation.

  • ② Multi-annual averaged indices. Flood disasters under climate change impact have contingency and uncertainty. Therefore, the flood and drought disaster data were multi-annually averaged.

  • ③ Evaluation indices for long sequence comparison. Due to the differences in the data availability of different indices and provinces (regions), the selected latest evaluation year is 2020. The data sources mainly include the China Water Resources Statistical Yearbook; the China Flood and Drought Disaster Bulletin; the Ecological Environment Status Bulletin; the Water Resources Bulletin; the Investigation and Evaluation of Water Resources and its Development and Utilization in China; and the Statistical Yearbook of Urban and Rural Construction.

The scoring results are based on the percentage score system. x represents the scores; then, x ≥ 90, excellent; 80 ≤ x < 90, good; 70 ≤ x < 80, moderate; 60 ≤ x < 70, passed; x < 60, failed.

In order to eliminate the dimensional difference between the indices, a 100% system was adopted for the scores of different indices. The reasonable thresholds need to be set to standardize the data. Different indices are standardized according to the different evaluation purposes and index connotations (Table 4).

• ① Original data. The original data can reflect the real conditions and can be used as a criterion for the evaluation system.

• ② Historical extreme data mainly include the flood disaster index. The evaluation purpose is to reflect the impact severity of the current flood disaster relative to the historical extreme event, in which 100 points are for the historical maximum value and 0 points are for the historical minimum value.

• ③ Expert decision-making. We invite international experts to evaluate the scoring threshold of indices according to the current situation in China.

• ④ Previous research. The index threshold was determined according to the relevant domestic and foreign studies.

The water security evaluation grades for all of the provinces were passed or overpassed, in which the proportion of excellent grades was 3.23%, only 1 province. The good grades accounted for the largest proportion, (67.74%), which are 21 provinces. The medium proportion accounted for 25.80% of the eight provinces. The passed proportion was 3.23%, only one province. As far as spatial distribution is concerned, the water security level under climate change impact in all provinces of northern China is significantly lower than that in southern China. Provinces with medium or lower water security scores are all located in northern China. The main reason is that the scores of both sustainability and water quality evaluations are lower than those in the southern regions of China. The lowest water security scores were concentrated in the Huang-Huai-Hai River Basins, including Hebei, Beijing, Tianjin, Shanxi, Shandong, and other provinces (regions).

The water security influencing factors are different in the different provinces. In order to find the main factors, and based on the evaluation scores of different dimensions, the cluster analysis method was used to classify the water security types of the relevant provinces. The entire water security series could be classified as different similar groups using the cluster analysis method. The significance test could determine if the property differences between classifications would be. Water security type classification and spatial distribution under climate change impact are shown in Figure 2.

• Class A. Sustainability vulnerable type. The most prominent water security problem of this type is low sustainability. The evaluation average scores were only 41.63. These kinds of provinces are mainly located in North China, with dense populations, developed industries and agriculture, and high economic development. However, the local water resources are relatively scarce, and the degree of water resource development and utilization is relatively high, Beijing, Hebei, and Tianjin in the Haihe River basin have serious problems with groundwater over-exploitation. In addition, the water quality in these provinces (regions) is not optimistic. The evaluation score is 74.49. The water quality standard rate in the rivers and lakes in these provinces (regions) is relatively low.

• Class B. Comprehensive vulnerability. Such kinds of provinces are mainly located in the northern part of China, including Xinjiang, Gansu, Ningxia, and Shaanxi, as well as Henan, Inner Mongolia, and Liaoning provinces. The main feature in these kinds of provinces is that water security dimension scores are relatively moderate, in which the mean value of quantity adequacy is the lowest in all of the classifications, only 79.65. The main reasons are the relatively low degree of water supply guarantee, the high drought rate, and the low proportion of the population with safe drinking water in rural areas. Sustainability evaluation scores were also low, only 74.33. The main reason is that these types of provinces are mainly located in northwest China, where the water resources are relatively poor, economic development is backward, the ecological environment is fragile, the evaporation is large, the river water loss is serious, and the exit discharge is low. At the same time, with the development of the social economy, there is an excessive development of water resources in some areas.

• Class C. Frail water quality. A small part of provinces belong to this kind of water security, including Jiangsu, Fujian, and Shanghai, which are located in eastern China. The comprehensive scores of water security and all dimensions in these provinces are very high, and the quantity adequacy, sustainability, and flood control safety guarantee have all reached excellent levels. However, the average score of water quality suitability is relatively low, only 78.51, which belongs to a moderate level. The water quality problem in Shanghai is particularly serious, all the river and lake water quality problems are not optimistic.

• Class D and Class E. Both belong to the frail flood control safety type. The flood control safety guarantee score for Class D is 73.14 and the lower score for Class E is 61.23. The overall water security scores for such kinds of provinces are good, sustainability is excellent. Such kinds of provinces are mainly distributed in the southern and northeastern parts of China, where precipitation is relatively abundant and the frequency of short-duration extreme rainstorms is high. Economic and human life losses caused by extreme rainstorms and floods have been relatively high in recent years.

Based on streamlining the definition, connotation, and dimensions of water security under climate change, this paper constructed the regional water security evaluation indices and applied them to water security evaluation under climate change impact in the 31 provinces (regions) of China.

• (1) Based on the concept and connotation of quantity and sustainability guarantee in water resource security, the evaluation dimensions of quantity adequacy and sustainability were put forward. The evaluation dimensions reflect the current and future water resource security situation. Compared with the single water resource endowment index, such evaluation dimensions can scientifically identify the real causes of regional water shortage, clearly explain the economic security connotation, and ensure the systematic perfection of water security connotation under climate change impact.

• (2) The relevant discipline background of water security under climate change impact was reasonably considered. Based on the hierarchical analysis and the experts' decision-making methods, and starting from the connotation of water security, the evaluation dimensions, including quantity adequacy, water quality suitability, sustainability, cost affordability, and flood control safety, were put forward.

• (3) Considering that the water security under climate change impact has both strong professional and policy requirements, the evaluation indices of water security under climate change impact were constructed both from the national policy level and professional technical level, respectively.

• (4) It is shown from the regional water security evaluation and cluster analysis that the provinces (regions) with the lowest water security evaluation scores are concentrated in the Huang-Huai-Hai (i.e. the Yellow River, the Huaihe River, and the Haihe River) River basins. The water security problems vary in different regions. There are high unsustainable risks in water resource development and ecosystems in all provinces in the North China Plain. The water quality is also not optimistic. There are certain risks in water supply and demand satisfaction, sustainability, and water quality in the northwest provinces. The water security evaluation scores in the southern provinces are relatively high, and there are mainly water quality and flood disaster risks. The water cost affordability all over the country is well and the regional difference is not significant.

The evaluation results clearly diagnosed the water security problems under climate change impact in China, which is consistent with the current situation. It shows that the evaluation indices have an important reference value in water security evaluation under climate change impact.

There are some limitations during study work, such as data spatial or temporal resolution and socioeconomic factors (population growth and urbanization, water management policies, regulations, and governance structures), as well as climate model uncertainties. Therefore, future potential studies should focus on addressing these limitations and further improving the robustness of water security evaluation indices.

The author consents to participate in the works under the Ethical Approval and Compliance with Ethical Standards.

All the data in the paper can be published without any competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

The study conception and design, material preparation, data collection, and analysis were performed by Ke Zhou.

Funding information is not applicable.

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

The authors declare there is no conflict.