Evaluation of Transboundary Water Resource Development in Mekong River Basin: The Application of Analytic Hierarchy Process in the Context of Water Cooperation

Mekong River is one of the major international freshwater sources in the world. The Lower Mekong Basin (LMB) comprised of four downstream countries, including Thailand, Lao PDR, Cambodia, and Vietnam. The utilization of the basin’s water brings not only substantial benefits to the region ranging from hydropower to navigation, but also negative impacts caused by the unbalanced water using. The essential role of Mekong River requires all member nations to cooperate effectively for the sustainable development of the region. One of the most popular methods in the field of water resource management is a trustable tool called the Analytical Hierarchy Process (AHP). AHP is much appropriate for water resource policymaking. The literature, however, points out that there is no study to both structure the water using hierarchy and employ quantitative (objective) criteria to the AHP model in LMB case. With regard to water resource management, there are no previous studies applying AHP models to evaluating sustainable development of transboundary water resource in LMB case. This paper explores the evolution of water cooperation among Mekong countries and subsequently evaluates the water development scenarios in the LMB based on the water cooperation preferences of four LMB countries This study proposes a novel approach to ana-lyzing, assessing water resource development scenarios characterized by sustainability indicators and to assisting in developing a suitable water policy in LMB according to the best cooperation scenario.


Introduction
Transboundary rivers, usually shared by two or more riparian countries, are vital to human life and global peace and security. A total of 286 transboundary rivers worldwide, accounting for 60 per cent of the world freshwater flow, are currently providing home and livelihoods for more than 40 per cent of the global population [1] [2]. Given the increasing demand for fresh water supplies due to climate change, rapid population growth and industrial development, transboundary water resource management have been widely recognised as a matter of growing concern across the globe. Therefore, water availability and usage in the international context present enormous challenges to water planners and decision-makers. Although differences in socio-economic development, political orientation, national self-interests and institutional and legal frameworks across member states are often considered potential sources of conflict, they open up opportunities for greater cooperation on technical, social and economic issues [3]. Empirical studies have indicated that riparian countries are more likely to cooperate than fight over water despite the coexistence of cooperation and conflict in the transboundary water context [4] [5]. Cooperation on shared waters is becoming more common for some reasons, including mutual interest, shared benefit and the existence of institutional arrangement [6] [7]. Many researchers have acknowledged the essential role of transboundary water cooperation in maintaining the peace and security of the region, providing substantial economic benefits to member nations through as well as increasing the balanced and equitable utilisation of the water resources [3] [8] [9] [10] [11] [12]. Scholars have identified enormous benefits from basin-wide cooperation by assessing the value of water cooperation in the international context [13] [14] [15]. In addition, the United Nations (UN) has highlighted the significant importance of transboundary cooperation in implementing integrated water resources management at all levels by 2030 by making this topic the focus of target 6.5 of Sustainable Development Goals (SDG) [8] [16]. According to Schmeier & Vogel (2018), member states tend to choose cooperation over conflict since the cooperation benefits in the long term will outweigh potential gains from noncooperative actions in the short term [17]. Considering the importance of cooperation, although transboundary river issues can be approached from various perspectives, a better understanding of these issues under cooperative interactions among member countries is becoming increasingly popular and attractive.
In the context of transboundary river management, past research provides different views relating to cooperation issues. Much research emphasis has been placed on figuring out the factors that contribute to the success or failure of shared river cooperation. While there are cases of good practice on cooperation in trans-boundary rivers, namely the Colorado River and the Rhine river [18] [19], examples of ineffective collaboration can be found in the Syr Darya and the Amu Darya rivers [20] [21]. Many studies have mainly focused on measuring and monitoring transboundary water cooperation using different sets of indicators [22] [23] [24] [25] [26]. Other authors have spent considerable efforts to identify and better understand the challenges and opportunities of transboundary river cooperation [27] [28] [29] and to analyse the benefits of cooperation on international rivers [11] [30]. Despite the growing literature on cooperation over shared water currently, not many empirical works have been done to capture the evolution of the cooperative scale and examine the influence of this change on the water-related decision-making process. In reality, the focus and degree of waterrelated cooperation among riparian countries have changed over time, with an increased emphasis on emerging issues and water development priorities in a specific period. Therefore, the decision-makers should direct their attention to explore the impacts of the evolutionary pattern of water cooperation on the river basin development.
The Mekong River is one of the longest and most significant rivers globally, stretching on the national territory of six states, namely China, Myanmar, Laos, Thailand, Cambodia and Vietnam [32] [33]. The river system is essential for the comprehensive development of the region since it offers member countries a vital source of natural resources while supporting rich biodiversity and the largest inland fisheries in the world [31] [34]. In terms of geographical location, the Mekong River Basin (MRB) is divided into two sub-basins: 1) the Upper Mekong Basin (UMB), consisting of China and Myanmar; 2) the Lower Mekong Basin (LMB), which starts from Laos to Vietnam (see Figure 1). The LMB, accounting for 76 per cent of the total area of the basin with a total population of around 65 million people, serves as a lifeline for the basin's inhabitants and economic development of all four lower countries by bringing enormous benefits from, such as water supply, hydropower generation, irrigation and navigation [31] [35]. Main characteristics of the MRB countries are described in Table 1 and Table 2. Table 1. Area of member countries in MRB [36].

Member country
Area of the country within MRB (km 2 ) As % total area of the basin (%) As % total area of the country (%)   Figure 1. Map of the Mekong River Basin [31].
Managing and resolving water-related issues among countries with different levels of development and interests while preserving and maintaining the gains from the river have been posing significant challenges to the LMB members, which require practical cooperation [37]. The cooperation history between lower Mekong countries has started in the early 1950s with considerable efforts of the United Nations to assist in forming the Mekong River Committee, the first largescale organisation aiming to promote cooperative water development relating particularly to security issues [38] [39]. However, it was not until 1995 that the birth of the Mekong River Commission (MRC), an international organisation established under 1995 agreement signing by the four lower Mekong countries has marked a historic turning point in the regional cooperative agenda. The mission of MRC is to facilitate joint development and ensure the reasonable and equitable use of water resources in the basin [40]. Similarly, water-related issues in the Mekong region are central to several cooperative mechanisms such as the Greater Mekong Subregion, the Lower Mekong Initiatives or the Lancang-Mekong Cooperation (Table 3).
Despite these institutional frameworks, the contribution that MRC has made to foster cooperation among the LMB countries is recognised as substantial [38] [42]. Till date, MRC, as a model of cross-border water management with its intense consciousness of comprehensive development rather than entirely emphasizing on economic achievement, has relatively succeeded in mitigating conflict and boost the riparian states' joint action on water-related issues [43] [44] [45].
Sustaining shared river collaboration is challenging; thus, concerned authorities need to consider the different dimensions of regional cooperation activities on the Mekong River to gain insights into the evolution toward transboundary water cooperation, consequently assist the decision-making process in the LMB. MRC, with its emphasis on the critical sectors in the LMB, has carried out several Table 3. Examples of cooperative frameworks in Mekong region (adopted from [40], [41] For all the above reasons, the primary goal of this paper is to explore the evolution of water cooperation among Mekong countries and subsequently evaluate the water development scenarios in the LMB based on the water cooperation preferences of four LMB countries. The author aims to achieve these objectives by answering the following research questions: 1) How has the cooperation over water in the MRB changed during the last 50 years, especially since the establishment of MRC in 1995, and 2) What are the preferred development scenarios of the four LMB countries taking the differences in water cooperation scale into consideration. A multi-criteria decision analysis model is employed for providing an in-depth analysis of decision-making processes in the case of the LMB, which are characterised by multiple criteria and alternative decision options.
The remainder of this paper is organised as follows. After setting the theme for this research in the introductory section, the theoretical framework is presented, defining the specific viewpoint regarding water cooperation in the context of the transboundary river and identifying the key variables that should be included in the evaluation. The following section introduces the research methodology, in which the research model and data collection process are carefully explained. Then, the nature of water cooperation in the LMB and the performance evaluation of development scenarios are accordingly analysed. The final sections discuss the findings and provide some concluding remarks.

Defining Transboundary Water Cooperation
Despite a large body of research done on cooperative interactions in a transboundary context, very few studies define or explain the term "transboundary water cooperation" carefully. There is no single definition of this term since it is interpreted differently by actors in different settings and can exist in a wide range of forms [12]. The United Nations Economic Commission for Europe, in their policy guidance, has regarded transboundary water cooperation as "the effective cooperation between two or more countries sharing a transboundary river, lake, or aquifer" [53]. Nonetheless, the actors involved in water cooperation activities and the cooperative forms have not been adequately identified in those definitions. Adeel et al. (2015) [54] state that "transboundary water cooperation covers various levels of interactions between and among parties, stakeholders, and sectors that are involved in the development, use and management of a water resource; in the delivery of water services; or are impacted from either the actions or the consequences of such involvement". Subsequently, after significant revision, M. J. McCracken (2019) [55] finally defined transboundary water cooperation as "interactions between actors over shared waters that result in establishing mutually beneficial outcomes through a decision-making process; this process could include formal and informal legal and institutional mechanisms depending on the scale and context". M. J. McCracken has successfully captured the legal and institutional basis of cooperation, making it easily applicable to different situations. To this paper, M. J. McCracken's definition is the most relevant, emphasising the essential elements required for full transboundary water cooperation.

Classifying Transboundary Water Cooperation
Early understanding of transboundary water cooperation has established a sound foundation for examining other facets of this term. Cooperation over international waters can take different forms at various levels of operation, which indicate the activities counted as cooperation. Types of cooperative efforts vary from 1) information sharing (data exchange) relating, such as reservoir operations, hydrologic information and flood/drought mitigation, 2) active collaboration in the form of notification/consultation in planned development to 3) joint actions (joint plans, investment or management) [12] [16] [35] [37] [56]. Existing arrangements of transboundary water cooperation differ significantly regarding the extent and intensity of cooperation [2]. An agreement/convention, bilateral/multilateral treaty, protocol, memorandum of understanding and joint declaration between riparian countries is referred to as an arrangement for transboundary water cooperation, which may be at different levels from ministerial to governmental and national to the regional level [57] (see Table 4). Similarly, to quantify the extent of collaboration Strategic Foresight Group (2015) [58] specified active water cooperation in low to high order, ranging from ministerial-level meetings, collaboration in technical issues, joint monitoring, high political commitment to regional integration. More specifically, Grünwald et al. (2020) [59], when taking the evolution of water-related events as crucial issues, pointed out six levels of cooperation intensity, including silent, exploratory, strategic, accountable, affinitive and intuitive cooperation. While most available literature has focused on the forms or arrangements of transboundary water cooperation, the main challenge that needs to be addressed in classifying water cooperation is how to measure the cooperative level. In practice, some previous researchers have proposed intensity scales to rank transboundary cooperative water events 1 . The first scale to measure the international conflict or cooperation intensity between nations was the 15-point COPDAB Scale introduced by Azar (1980b) [61]: point 1 represents the most cooperative event, and point 15 represents the most conflictive one [62]. However, the most renowned scale is the BAR Scale 2 , which was developed in the Basin at Risk (BAR) project of Oregon State University to evaluate the intensity of conflict or cooperative events occurring in the period 1948 to 1999 [63]. BAR scale-origi- 1 This study uses the definition of water cooperative events proposed by Yoffe et al. [63], in which cooperative events are defined as instances of cooperation that occur within an international river basin, involve the nations riparian to that basin, and concern freshwater as a scarce or consumable resource (e.g., water quantity, water quality) or as a quantity to be managed (e.g., flooding or flood control, water levels for navigational purposes). water cooperation in the Lancang-Mekong River Basin. In this study, the author will introduce a 5-point scale to evaluate the evolution of water cooperation in the LMB in forty years, combining the BAR and Feng scale 3 [65]. More specifically, while using the full Feng scale to create the new scale, only the BAR scale representing the cooperative levels from +1 to +7 point will be included ( Table  3). The reasons for selecting the two scales are 1) to make it comparable between them; and 2) to ensure consistency between the cooperative events and their respective scales since this study employs the cooperative event datasets constructed by the BAR project and Feng et al. (2019) [65], as will be explained later on in Section 3.1.

Multi-Criteria Decision Analysis-Analytic Hierarchy Process Approach
Transboundary river management is generally recognised as a difficult task due to the complexity of socio-economic systems, involving various stakeholders pursuing multiple and sometimes conflicting objectives [66]. Therefore, the decision-making process in the international river context requires considering various quantitative and qualitative criteria measured in different units while attempting to evaluate and compare the performances of various water-related alternatives. Scholars have developed methods to support making decisions in those situations, especially techniques capable of improving the audibility and transparency of the decisions. Multi-criteria decision analysis (MCDA) has been demonstrated as beneficial for solving international water-related matters, characterised by multiple criteria and alternative decision options [67]. Flexibility in analysis design [68] and the ability to improve transparency in decision procedure [67] is typically seen as the appeal of the MCDA method. This method proves to be a powerful approach to facilitate collaborative processes [69] [70] and considerably improve the decision-making process and public acceptance [71]. MCDA consists of different approaches and analytical tools that allow stakeholders to rank and evaluate different alternatives against multiple criteria while considering their preferences [72]. Over the last few decades, the application of MCDA methods has increased and advanced significantly [73]. Particularly, MCDA has been mentioned as a critical component of decision support system in the field of water resources management [74]- [79]. In this field, water policy evaluation, planning of water supply, selection of infrastructure have been the most common applications of MCDA before 2007 [67]. Water shortage problems, water use management, water quality problems and water allocation are recently primary topics for publications using MCDA methods [80].
There are a large number of MCDA approaches that can be applied to cope with water-related issues. One of the most commonly used techniques is Analytic Hierarchy Process (AHP), developed by Saaty (1980) [81], a flexible and effective tool to solve complex problems and support the strategic decision-making process in many fields, such as in economics [82] [83] [84], healthcare [85], social science, engineering [ [93]. The motivation behind the development of AHP has not been only by its simplicity to combine quantitative and qualitative criteria in the priority-setting process [94] [95] [96], but also by its ability to make qualitative criteria measurable for prioritising or producing relative importance [97]. The basic concept of AHP describes the selection process of the best (more beneficial) alternative concerning each criterion. An AHP model comprises the following steps: 1) Constructing a model for the decision: a complicated decision-making problem is decomposed into a hierarchical structure of goals, criteria and alternatives.
2) Deriving weights for the criteria: Through pairwise comparisons of the relative importance of each set of criteria regarding the expected goal, the weights of criteria are obtained.
3) Deriving priorities for the alternatives: By following the same process as described in Step 2 (i.e., making pairwise comparisons of alternatives concerning each criterion), the alternative priorities are obtained, and then the overall priorities of all alternatives are established, taking into account the weights of criteria.
The pairwise comparisons are made using a ratio scale proposed by Saaty (1977) [81] ( Table 5). The consistency ratio is calculated to guarantee a reasonable and acceptable consistency level. In the case that inconsistency happens, a review and revision of judgements are required.  [91] stresses the potential applicability of the AHP model to integrate stakeholders' preferences into the selection process of different water resources management plans in the lower Incomati river basin a shared river between Mozambique, Swaziland and South Africa. Other scholars attempt to solve the water allocation problems in transboundary river basins, such as identifying the best water allocation strategy or developing an effective benefit-sharing mechanism for water allocation between riparian countries [97] [110] [111].
There has been no study on water resources development in the LMB case, especially evaluating the water scenarios proposed in the Council Study. As to analysing the AHP model used in water resource management by application objectives, there are three groups consisting of selection, prioritisation and evaluation issues.
Supporting the decision making relating to the evaluation problem is highlighted as the most frequent application of AHP [92]. In this paper, different water development scenarios in the LMB will be evaluated by the economic benefits that riparian countries can receive from the major water-related sectors considering these countries' preferences for each sector. Therefore, a traditional economic approach to accessing alternatives is insufficient for that purpose, particularly when applying to evaluate against a range of economic criteria with different measurement units. A new approach, which can accommodate qualitative factors while maintaining the significant effect of economic issues and, simultaneously, can be transparent and easy enough to implement while avoiding biased judgements, is much needed. Under those circumstances, AHP is believed to fulfill all the requirements as a promising solution to the decision-making problem in the transboundary river basin.

Water Cooperation Event Database
Previous researchers have spent considerable efforts to compile global datasets 4 MCDM is also known as MCDA and these two concepts are generally used interchangeably. N. P. Lan on interactions between states, involving both conflict and cooperative interactions, that can contribute to the study of cooperation over international river basins, either directly or indirectly. In addition to the Conflict and Peace Data Bank (COPDAB) 1948-1978 [61], there are some other datasets, for example, Global Event Data System introduced by the Global Database of Events, Language, and Tone (GDELT) project and Environment and Security Water Conflict Chronology developed by Gleick (1993) [112]. However, while many of those datasets mainly focus on diplomatic and military interactions between countries, none specifically pay attention to water interactions in transboundary river basins. The International Water Event Database (IWED) 5 developed from the Basins at Risk project of Oregon State University is recognised as the first attempt to provide a global description of water interactions over the transboundary river between riparian states [4] [113] (see Table 6). IWED is an online searchable database that reports conflict and cooperative events occurring in Table 6. Examples of water events in the MRB from BAR water event database (extracted from http://gis.nacse.org/tfdd/internationalEvents.php and the author's self-analysis).  (1975-1995 and 1995-2015) are subsequently compared and assessed for trends in international water cooperation in the LMB. The author produced a new cooperative scale combining the BAR and Feng scales to make the two datasets comparable. The author first carefully investigated the IWED and LWCED scale descriptions to identify the differences and similarities of the events assigned to each cooperative level in these two datasets.
The events with similar characteristics (or belongs to a similar cooperative form) were grouped to produce a new cooperative level, assigned a particular point. A new 5-point cooperative scale was introduced at the end of this process (Table  7). In addition, it should be noted that the objectives of water cooperation events reported in the two datasets are diverse and partly different. To construct a new event dataset, this study, thus, selects only the water events concerning the same cooperative objectives in the two datasets, including hydropower, navigation, water use, joint management and comprehensive development. Finally, the cooperative point of each objective was calculated by multiplying their frequencies with their cooperative levels to explore the preference of riparian countries on each cooperative objective.
This study expands the current literature on water cooperation in the MRB in

Identifying Evaluation Criteria and Alternatives
As pointed out earlier, this study aims to evaluate water development in the LMB using the main development scenarios derived from the Council Study of MRC. Therefore, three main scenarios, which are characterised by different levels of Journal of Water Resource and Protection Consensus-a medium level, and indicates that parties are cooperating to reach some common targets. International Freshwater Treaty; Major strategic alliance (regional or international): joining or organizing international alliances 6 Agreement-indicates that parties have adopted a formal inter-governmental agreement. 7 Voluntary unification into one nation: Merging voluntarily into one nation (state); forming one nation with one legally binding government. In addition to the development described in scenario M2, all water resources development that is planned in hydropower, agriculture, land use, biodiversity, flood control… are included in this scenario. On a timescale, this scenario covers the expected development occurring by 2040 if fully implemented.
M3CC is a sub-scenario derived from scenario M3, adding the estimated climate change condition (warmer plus seasonal change). Table 8 summarized the major characteristics of four water development scenarios utilized in the AHP model of the LMB.
After identifying the alternatives (development scenarios) of the AHP model, it is necessary to select the appropriate evaluation criteria. Even though riparian countries follow their plan to exploit a shared river, given the importance of the river to national development, it is understandable that the starting point for any consideration of cooperation is generally associated with the legitimate goals of extracting maximum benefits from the river. In this regard, economic benefits are frequently the primary justification for deciding water issues, particularly on hydropower development, one of the most significant matters of concern in the LMB. This study thus utilises criteria representing the economic benefits of different sectors to assess three main scenarios, noticing that those benefits are not assigned direct but indirect forms of economic value where data is not sufficient.
The LMB countries have widely agreed upon the potential areas for cooperative development, which are also highlighted in many reports and working papers [115].

• Hydropower
Despite concerns relating to environmental issues, hydropower still plays a significant role in the economic growth of the LMB countries, serving both local and export markets and representing 10% of the electricity demand of member countries [31]. From 2005 to 2015, the hydroelectricity production in the LMB increased around 3.5 times, from 9.3 to 32.4 GWh, reaching a gross value of more than USD 2 billion [116]. By 2015, 59 hydropower projects developing in the LMB had provided up to 35% of the total hydropower potential estimated for  [41].

• Fisheries
Fisheries in the MRB, which comprises the world's highest production volume, is a vital source of food and livelihood for the people in the basin [42] [116].
In 2015, the total capture fisheries production in the LMB, which constituted 45% of four riparian countries' national output on average, was valued at USD 11 billion [31] [116].  [31]. The navigation sector is expected to increasingly contribute to the basin's economic development, especially to the economic growth of Cambodia and Vietnam [116].

• Flood control
Since severe floods in the MRB have led to devastating consequences and flood damages is expected to increase five to ten times by 2040 [116], flood control is becoming more and more essential to the development of the LMB. Therefore, this study attempts to qualify the effect of flood protection for different scenarios to present the economic benefit of the flood control system.
As a consequence, four criteria along with nine sub-criteria were selected (Table   9), and a hierarchical structure describing the decision-making problem in the LMB was introduced ( Figure 2). Table 9. Identified criteria for evaluating water development scenarios in the LMB.

Weighting Criteria
Once the hierarchy has been constructed, pairwise comparisons, which includes comparing each criterion with all the other criteria at a particular hierarchical level regarding the ultimate goal, are used to identify preferences (relative weights) in the AHP model and, accordingly, a matrix with pairwise comparisons of criteria is formed as illustrated in Equation (1) where ij a     = the Saaty's point for comparison between criterion i-th and criterion j-th (i, j = 1, 2, ..., n), and ij a     indicates the relative importance of criterion i-th when being compared with criterion j-th, Pairwise comparisons are made to obtain each criterion's relative weight (rel-N. P. Lan ative importance) in relation to the other criteria, using Saaty's scale. Decisionmakers commonly perform this process making their judgements based on their preferences when considering two criteria simultaneously.
Due to the differences in the perception of the importance of criteria, the weights assigned to a particular criterion may largely vary, which subsequently causes the inability of decision-makers to give such an accurate and rational evaluation.
To overcome this major drawback, the author presents a so-called "cooperative point" developed to determine the relative weights of criteria, which to the best The cooperative points of all criteria are clearly presented in Table 10.
• Second, the differences in cooperative points between each pair of criteria are calculated by following equation: where: ij ∆ = differences in cooperative points between criterion i-th and criterion j-th.
The pairwise differences of cooperative points are illustrated in Table 11.  • Third, the differences in cooperative points are transformed to a so-called "relative Saaty's points" using a combination between Saaty's scale and fol- where: S ij = relative Saaty's point of pairwise comparison between criterion i-th and criterion j-th, which indicates the relative importance of criterion i-th over criterion j-th when making a pairwise comparison.
This formula assures to limit the relative Saaty's point within the range of values from 1 to 9, which follows the 9-point Saaty's scale. Accordingly, the relative Saaty's points will be normalised to original Saaty's points (Table 12).
This new method of determining the relative importance of each criterion differs from the traditional method by assuming that: 1) Pairwise comparisons are made by considering the cooperative point of two criteria at one time rather than deriving from decision-maker evaluation, and 2) the more the cooperative point of a particular criterion (water-related issue) is, the more important it is with respect to the other criterion.

Checking Consistency of the Pairwise Comparison of Criteria
The AHP model's consistency test is presented using the theory of maximum eigenvalues derived from eigenvectors of pairwise comparison matrix of criteria, and the consistency index and consistency ratio proposed by Saaty (1980) as follows:  Table 13.   And, finally, the obtained CR is acceptable if the CR is less than 10% (0.01). If the obtained CR > 0.01, the pairwise comparisons should be revised and adjusted. At the end of this step, the local priorities of all alternatives with respect to each criterion are derived.

Ranking the Alternatives and Reaching the Conclusion
In the last step, the alternatives' overall priorities are obtained as a weighted-sum taking into account each criterion's weight the local priorities of the alternatives.
The ranking of the alternatives is presented, and the alternative at first rank is the best choice.

The Evolution of Water Cooperation in the MRB
The following sections detail the key findings relating to water cooperation issues in the MRB before and after the establishment of MRC. Cooperative objectives, along with their distribution and frequency and intensity distribution of water cooperation events, are discussed separately in order to highlight the noticeable differences between the two time periods and describe the historical patterns of water cooperation in the MRB.

Objectives of Water Cooperative Events
As can be seen from Table 14, over forty years , water cooperation events in the MRB encompassed a wide range of aspects of water resource management, from general objectives to very particular ones. While mainly focusing on six cooperative issues from 1975 to 1995, the MRB countries extended their cooperative objectives to a much broader spectrum in the next 20 years, covering the sustainable development issues of the basin, such as flood control and environmental conservation. It was observed that four issues-hydropower, navigation, water quantity/water use and joint management are the popular water-related N. P. Lan Journal of Water Resource and Protection

Distribution (Frequency) of Water Cooperation Objectives
It should be noted that the number of water cooperation events that occurred followed by joint management (24%) during the 1995-2015 study period ( Figure   3). This finding shows a similarity with a study by Wei et al. [118] that confirms the significance of hydropower as one of the vital cooperative topics in MRB that appeared in newspapers from 1991 to 2018. Remarkably, before the establishment of the MRC, special attention was given to cooperation on water quantity/water use in the Mekong River, which made up 26% of the total cooperative objectives.
In contrast, this was a matter of much lower concern in the next 20 years, comprising only 6% of all cooperative events. The data also indicate that navigation events were more frequent after 1995, and the proportion of cooperative events associated with navigation has more than doubled from 6% to 15% in forty years.

Cooperation Intensity Distribution
As explained in Section 3.1, a 5-point cooperative scale was introduced combining BAR and Feng scale to compare the two event datasets. Thus, in this section, the cooperation intensity distribution will be analysed based on this new scale to depict the diversity in cooperative levels of water events in two time periods. 1) In the period 1975-1995 From 1975 through 1995, cooperation on hydropower, water quantity and infrastructure development occurred at the intermediate level (3-point) (Figure 4). For example, medium cooperative events concerning those three issues comprised at least 56% to 75% of the total events related to each topic. Notably, although there were minimal economic development and navigation events before 1995, all of them occurred at a relatively high cooperative level (3-point) compared to other events. In contrast, more than 50% of events related to joint management, the most frequent cooperative issue, was primarily recorded at the lowest cooperative level (1-point).
2) In the period 1995-2015 About the distribution of cooperative levels during the 1995-2015 study period, extremely cooperative events (5-point) mainly spanned objectives relating to hydropower, joint management and navigation, while environmental conservation was the only issue with no event at the highest cooperative level ( Figure  5). In particular, 52% of hydropower events, 33% of joint management events and 31% of navigation events were extremely cooperative. Across all cooperative events, the number of events that occurred at the lowest cooperative level, on the contrary, comprised only 14% of the total. In addition, although there were minimum events concerning fisheries, all of them were at the highest cooperative level.   Table 15).
The data in Table show the rankings of five regular water-related cooperative objectives in the MRB based on their cooperative points 6 . It can be concluded that water cooperation in the MRB has significantly evolved after establishing the MRC. Before 1995, joint management was the most significant issue to crossborder cooperation between MRB countries, followed by water quantity/water and navigation proved to be the least preferred issue in the cooperative scheme of the MRB states. While hydropower ranked in third place on the priority list of water cooperation in 1975-1995, it stood at the first position, with joint 6 The calculation of cooperative points was previously explained in Section 3.1.   Accordingly, the relative weights (priority vector) of the main criteria were obtained using the normalisation principle with the acceptable results of pairwise comparisons equal to 0.07 (less than 0.1). As shown in Table 17, objective C1      2) For the four LMB countries Tables 19-22 described the global weights of criteria and the scenarios' final ranking of four LMB countries in detail. Generally, the preference orders of development scenarios are the same for all countries, with the ranking order from the best to the worst was M3CC, M3, M2 and M1. Similar to the LMB case, although M3CC, the most favourable scenario, was of higher priority than the second-ranked scenario M3, the difference in performance scores between them was pretty low in each country's case. In contrast, considering the two last-ranked scenarios, M2 and M1, M2 was valued much higher than M1 (approximately three to four times higher than M1). Scenario ranking was different across countries when considering each main criterion. For instance, M1 was the most,  and M3CC was the least beneficial scenario if valued against criterion C4 (fisheries) in any case. Therefore, it can be realised that the total benefit that the LMB countries receive from the basin is increasing over time, but the benefit derived from each sector might differ.

Discussion
It is essential to understand the evolution of water cooperation in transboundary river context to be able to explore the impact of riparian countries' attitudes towards cooperation on the evaluation of different development scenarios. This paper presented an insightful analysis of water cooperation activities in the MRB from 1974 to 2015 and assessed water development scenarios in the LMB. As the findings have shown, there have been substantial changes in cooperative objectives and levels between the MRB countries when comparing two periods of time (1975-1995 and 1995-2015). The considerable increase in the number of cooperative events and the further extension of issues discussed across the time indicates the willingness and commitment of member states to collaborate for the comprehensive development of the basin. Although each country has its emphasis on utilising Mekong River water, it is common for Mekong countries to cooperate to ensure regional water security and enhance their national strengths.
More importantly, the progress on cooperation between Mekong countries, illustrated by the higher cooperative levels on all issues, shows that institutional mechanisms like the MRC can help address the water-related matters of significant concern and foster inter-state cooperation. The establishment of the MRC N. P. Lan under the signing of the 1995 Agreement has provided essential support for member states to cooperate more actively and closely, as also emphasised in research by Schmeier [119]. By facilitating communication between riparian countries and ensuring compliance with other international laws and rules [120], MRC helps to build mutual trust and provides a solid basis for further cooperation between countries. The findings provide evidence to dispel the doubt by previous researchers like I. Campbell (2009) regarding the MRC's contribution to enhancing regional cooperation.
More specifically, the analysis of water cooperation in the MRB portrays the following basic characteristics of evolutionary cooperation in the basin.
1) Hydropower is recognised as the critical issue for cooperation along the Mekong River, as similarly highlighted by a study of (Wei et al., 2021) that hydropower is the most frequent topic of cooperation in the Mekong basin. The overarching impact of hydropower development on various water-related sectors, such as navigation, irrigation and fisheries, provides more potential space for cooperation negotiations.
2) The Mekong countries have been transitioning from initial cooperation, focusing on matters of national interest like hydropower and water quantity, to indepth collaboration concerning the environment and human beings. This substantial change coincides with member states' perceptions toward the importance of maintaining mutual benefit and sustainable development of the basin.
For the LMB's assessment of water development scenarios, the assessment results describe a common trend to both the basin and member states towards the ranking of four scenarios. Note that not only water resource development but, more importantly, the future development of hydropower projects in the mainstream of the Mekong River were included in the scenarios. Since hydropower was the issue of highest priority to all member states and the AHP model only concentrated on the economic benefit brought by main sectors, M3 and M3CC, the scenarios formulated with the existence of a large number of hydropower dams, are the two most beneficial scenarios to all LMB countries.
This study sets out to develop a framework to integrate the evolution of riparian countries' attitudes toward water cooperation into the process of evaluating water development in a transboundary river context. The analysis result of water cooperation in the MRB is constrained by the scope and the length of time coverage of the dataset on water cooperative events. The availability of more recent and updated data extracted from the various dataset on water interactions in the international river basin will help to gain a proper understanding of progress on inter-state cooperation between Mekong countries. Moreover, to make the results of pairwise comparisons of the AHP model more practical and meaningful, it is essential to consider cooperative water events but also the conflict zones due to the inevitable coexistence of cooperation and conflict in the context of transboundary river management. With the limitation of current data available on the monetary benefit of key water-related sectors in the LMB, the number of criteria selected for the AHP model is relatively small. Irrigation is also one of the sig-nificant economic activities in the Mekong River but is not included in this study, leading to inappropriate evaluation. As the model is applied to more cases, an adequate set of criteria should be employed and, also, different scenarios underestimated climate change situation and human activities should be incorporated into the AHP model to produce a comprehensive assessment result.

Conclusions
Water cooperation is broadly regarded as a valuable method to resolve disputes over shared waters and a prerequisite for facilitating river basin's sustainable development. By capturing the advancement in cooperative scales and objectives, this paper presents an insightful overview of the gradual transition in the MRB's cooperative scheme to underpin future transboundary water management and negotiations in the basin. The evaluation of water development scenarios in the LMB is of significant importance, as it serves as the basis for basin planning and supports the decision-making process. There exists a strong need for implementing economic assessment of shared water to enable more practical river planning and provide economic incentives that can affect the riparian countries' attitudes [121]. This study has shown the applicability of the AHP as a potential method to making decisions in the transboundary river context. Furthermore, this method appears to be effective in incorporating stakeholders' perceptions into the decision-making process.
The analysis of water cooperation in the MRB suggests several implications for policy-makers. Firstly, due to the rapid changes of climate, hydrological condition and geopolitical sensitivity of the Mekong River, cooperative activities in the Mekong River should focus on water security matters, increasingly becoming solid incentives for collaboration between member states. Cooperation on issues concerning water security with the involvement of all Mekong countries can mediate national interests, which, in turn, will help to resolve conflicts over water in the MRB [122]. Cooperative security implies strengthening both national and regional security as a whole through communication and cooperation. Secondly, since the international organisation like MRC is considered the legal backbone of international cooperative efforts, the role of the MRC should actively provide member states with a clear cooperation plan that can attract member states' willingness to join. Besides, water cooperation in the Mekong River should be regarded as a helpful resolution for any conflict over water in the basin. Thirdly, although bringing more economic benefit to the LMB countries, planned development scenarios in the LMB should also be carefully examined based on the inter-sectoral impacts to show a complete evaluation of future development of the LMB. This study can be further expanded to 1) explore and estimate the future evolutionary pattern toward both cooperation and conflict over Mekong water to address the significant issues that riparian countries should take into account in their planning process; 2) focus on other economic sectors in the LMB to provide a more extensive assessment of development scenarios. N. P. Lan