Resilience assessment methodology of urban water supply and sanitation systems integrating climate change and extreme events: a case study in Bangkok, Thailand Open Access

The United Nations Sustainable Development Goal 11 ‘Make cities and human settlements inclusive, safe, resilient and sustainable’ may be achieved through a simultaneous effort to address important issues and one such is maintaining sufficient and compliant performance of urban water cycles (United Nations 2023). To maintain an adequate level of service in urban water cycles, it is vital to consider the infrastructure within the urban water supply and sanitation (UWSS) system. The main motivation in considering UWSS system infrastructure is to ensure that the system can adapt to changes in land use and ecology of the area and demographic changes in population, coupled with hydrological and meteorological changes brought about by climate change and the onslaught of extreme events (World Health Organization 2009). The creeping effects of climate change and extreme events in urban centers are more blatant, due to their impact in hampering the quality of life of its inhabitants. Intermittent access to water supply and the existence of water-borne diseases in urban areas due to existing stressors have made climate change and extreme events a more serious threat (World Bank Group 2018).

Currently, there is a clamor for incorporating sustainability and climate change adaptation strategies into UWSS systems worldwide, most especially with the numerous evidence of the effects of climate change and extreme events in the maintenance and development of water supply and sanitation infrastructure (United Nations 2023). According to a study by the World Bank in 2010, gaps in climate change assessment have been found in many urban centers, where physical damages were rampant and operations were severely halted in terms of water supply and sewerage operations during extreme meteorological events (Danilenko et al. 2010; Sakai et al. 2020). In this regard, aspects of climate change adaptation must be investigated and operationalized to incorporate concepts such as resilience, adaptation, and vulnerability into asset management plans for UWSS systems (UNDP-UNEP Poverty-Environment Facility 2011).

In incorporating resilience, the World Health Organization explicitly stated in their report titled Vision 2030 the need to consider resilience in prolonging the operations of water supply and sanitation infrastructure systems, especially during extreme events, when communities are under stress. The report also mentioned relevant research gaps, such as providing resilience assessment methodologies for water supply and sanitation systems worldwide (World Health Organization 2009). Resilience assessment, as prompted by Vision 2030, has been done in different forms and various individual components of the UWSS by other researchers. However, there are not many resilience assessment methodologies that are developed and used in assessing the resilience of these individual components as a system in highly urbanized cities, where there are varied water supply and sanitation systems, depending on the characteristics of the urban area. Therefore, the main objectives of this study are: (1) to propose a methodology for developing an index-based multi-criteria conceptual resilience assessment framework of UWSS system infrastructure management that can be replicated in various areas of highly urbanized cities and (2) to deliver a step-by-step demonstration of the methodology in a highly urbanized city such as Bangkok, Thailand. The audience of this research is water resource managers and regulators who require support in assessing the resilience of UWSS systems and evaluating their performance in relation to climate change and extreme events, using a conceptual multi-criteria methodology.

To achieve the study objectives, the study design comprises the following activities, namely: Literature review, defining resilience in UWSS systems, development of resilience dimensions, development of methodology on resilience assessment, and application of the methodology in a case study area. In conducting a literature review, references and research gaps were identified on topics such as the definition of resilience and assessment frameworks of UWSS systems. Articles and research work from 2009 to 2023 that were selected also focused on multi-criteria resilience assessments of UWSS systems in various cities worldwide. After identifying the gaps in research from the literature review, the resilience of UWSS systems was defined to provide alignment to the dimensions that shall be measured in the multi-criteria framework methodology. In parallel, the various resilience dimensions of UWSS systems were also identified from the literature review as a basis for indicators that shall be determined in the methodology presented. Consequently, the methodology for resilience assessment framework development was done for application to Bangkok, Thailand.

The main statistical analysis for the conceptual resilience framework was done using the analytical hierarchy process (AHP) method developed by Saaty to determine the weights of the dimensions and indicators developed in the framework. AHP is a method used in multi-criteria decision-making due to its systematic approach in decomposing the aspects to attain the main goal of the decision through comparing judgments and reaching an effective decision through appropriate synthesis of priorities (Saaty 1986). Moreover, the AHP method also has a countercheck for measuring inconsistency in the hierarchy rated by chosen experts such as the consistency ratio (CR). To ensure the consistency and validity of the results obtained from the respondents, the acceptable CR must be below 20% (Saaty 1987; Goepel 2013; Talampas et al. 2023). The data for the AHP was gathered using an online survey constructed using Google Forms. The survey was first refined through a pilot among immediate peers and colleagues. After refinement of the survey tool, the survey was distributed to various global experts through electronic mail from June 2023 to August 2023. The developed survey tool had several categories and questions were formulated based on the format of the AHP method (Saaty 1986). In this study, only the dimensions and indicators of the framework were subjected to AHP for weighting, while the variables were assigned equal weights. This approach ensures greater flexibility in cases where data to define the indicators may be lacking and helps keep the AHP survey concise. For the sampling criteria, eligible experts must have handled research work or projects related to any or all aspects of UWSS systems for the past 5 years.

In the development of the methodology of resilience assessment, a literature review of several multi-criteria resilience assessment frameworks was undertaken. Vision 2030 served as a high-level guide in determining the steps in resilience assessment of water supply and sanitation infrastructure, that was first piloted in rural areas (World Health Organization 2009). On the other hand, the United Nations International Children's Emergency Fund (UNICEF) Framework provides a general methodology on how to assess water supply and sanitation systems to determine resilience. The methodology involves the steps on how to understand the existing system, identifying salient features, and determining the risks in the operation of the system. The methodology includes a three-category rating system to determine which technologies are resilient to various levels of climate change impacts (UNICEF and Global Water Partnership 2015). General methodologies give an insight to managers on how to make a more profound analysis and outlook on the UWSS systems and its relationship to risks due to climate change and extreme events.

After Vision 2030's initiative, several multi-criteria frameworks were developed by other scholars. These multi-criteria frameworks were focused on only one set of indicators to determine resilience and other aspects of risk assessment, depending on the field of analysis. For instance, Heath et al.'s (2010) assessment framework titled ‘Rapid Climate Adaptation Assessment’ (RCAA) introduced indicators for resilience that are based on monetary and non-monetary capital investments of water supply and sanitation infrastructures located in urban poor communities. The RCAA framework was tested in Lusaka – Zambia, Naivasha – Kenya, and Antananarivo – Madagascar (Heath et al. 2012). Karamouz et al. (2010) provided a vulnerability assessment method that integrated resilience in the framework. In this study, the assessment method included a detailed checklist and algorithm for developing adaptation strategies in water supply systems. Indicators that were used in the assessment include the state of the water supply system and its critical assets, a list of existing plans for risk and disaster reduction, and a review of the history of adverse extreme events in the area (Karamouz et al. 2010). The said framework was applied in an unnamed city for privacy purposes and included an evaluation of water supply-related infrastructure (Karamouz et al. 2010).

Lorz et al. (2012) included in their Driving forces-Pressures-State-Impacts-Responses (DPSIR) approach an overall assessment of the various factors that affect the resilience and management of water resources in Central Brazil. The status of the water supply infrastructure components and related indicators were emphasized in this framework. For wastewater management, Astaraie-Imani et al. (2012) developed a one-level resilience assessment framework titled Integrated Urban Wastewater System (IUWS) model to determine the effect of climate change and urbanization stressors on the various water quality and volumetric indicators of resilience and vulnerability.

Apart from single-level multi-criteria frameworks, later years considered multi-level resilience assessment frameworks where more criteria were introduced and sorted according to arbitrary categories. Gonzales & Ajami (2015) developed the Urban Water Sustainability Framework, which focuses on the assessment of the sustainability of water sources. Indices to describe each indicator were also included in the framework and were applied to the San Francisco Bay Region (Gonzales & Ajami 2015). A similar framework was developed by Howard et al. (2021), where several domains were defined and established to be used as major categories of indicators and assess the performance of the water supply and sanitation systems (Howard et al. 2021). Such indicators also have normalized ratings that help action items for improvement of water supply and sanitation systems. The framework was applied in areas of Nepal and Ethiopia, where resilience was rated based on the technology adapted in the country (Howard et al. 2021). Saikia et al. (2022) developed the City Water Resilience Framework, a two-level multi-criteria resilience assessment framework that included four dimensions. Although the framework is multi-criteria, the scoring system is based on the goal setting of the community. The framework and scoring system were applied in Cape Town and Greater Miami and the Beaches (GM&B), where the results were used for water resources planning and management improvements (Saikia et al. 2022).

While numerous frameworks exist, the studies reviewed focus on either water supply or sanitation, in rural and semi-urban areas, without integrating both components as a system. The primary advantage of the methodology in this study is that it provides a set of step-by-step guidelines on how to assess climate resilience in their infrastructure using existing resources. Moreover, the methodology offers a comprehensive guide on how to integrate both UWSS infrastructure as one system. Another advantage of this study is that the methodology also emphasizes the inclusion of existing and established water utility and sanitation performance indicators. This approach ensures that organizations can easily adapt the framework to their current operations (Sakai 2024). By aligning resilience assessment with existing management systems, the methodology encourages water utilities and government agencies to adopt and implement the framework effectively.

As a pre-requisite in developing the methodology, there is a need to define resilience in terms of UWSS systems and their relationship with climate change and extreme events. Based on the definitions in the literature review, this study defines UWSS system resiliency as the following: ‘Urban water supply and sanitation systems resiliency is the capacity of its vital components to recover when the system is subjected to sustained stressors driven by climate change, extreme events or any other significant disturbance’.

To quantify resilience, dimensions were defined based on the common categories of indicators in previous resilience assessment frameworks and their relevance to determining the overall performance of UWSS systems. The dimensions of the UWSS presented are (1) ‘Water availability and urban waterways management’ (D1), (2) ‘Infrastructure operations’ (D2), and (3) ‘Quality of service’ (D3). For this study, the ‘Water Availability and Urban Waterways Management’ (D1) dimension is defined as the state of the water source and the management of existing waterways in the immediate urban area being served by both water supply and sanitation infrastructures, subjected to climate change. ‘Infrastructure Operations’ (D2) is the dimension that is defined as the status of operational procedures of water supply and sanitation infrastructures. Lastly, the third dimension is ‘Quality of Service’ (D3), which is defined as the quality of output from the water supply and sanitation infrastructure system.

In Stage 1: Understanding the system, the goal is to thoroughly understand the UWSS system for assessment to determine the scope of the framework to be developed. As shown in Figure 2, two parallel actions are recommended for the user of the framework, namely: (1) ‘System components definition’ and (2) ‘Urban area climate stresses’. ‘System components’ is defined as the action where users will identify the ‘hard’ components of both water supply and wastewater systems, labeled as ‘Identification of infrastructure components’, and the operations and beneficiaries of the current water supply and wastewater systems, labeled as ‘Stakeholders of the system’.

In identifying the infrastructure components, there are two categories: (1) ‘Water supply system’ and (2) ‘Wastewater systems’. For water supply systems in urban areas, the user should identify the centralized water sources and treatment facilities, decentralized water sources and treatment facilities, and the water supply distribution system. In smaller urban areas, groundwater sources and on-site treatment facilities may be more prevalent, while in megacities, surface water sources with centralized treatment facilities are more applicable. In terms of distribution, urban areas with lower-income customers might only have communal water supply systems, while high-income urban areas may have piped water for individual connections.

For the wastewater systems in urban areas, aspects to consider in the assessment include (1) ‘Wastewater collection/combined sewer systems’, (2) ‘Centralized wastewater treatment plants’, and (3) ‘Decentralized wastewater treatment systems/methods’. These aspects must be considered by the user since wastewater systems vary greatly depending on factors such as population density, land area, availability of technology, and other related factors. In older urban areas, wastewater collection often relies on septic tanks. Newer or high-income communities may have combined sewer systems or fully-sewered areas. It is also important to consider the wastewater treatment methods used in these urban areas for assessment, whether they utilize centralized or decentralized treatment systems.

For the ‘Stakeholders of the system’, the users of the framework must also identify important stakeholders, such as the (1) ‘Management of water supply and wastewater utilities’, (2) ‘Demographics of the population served in the urban area’, and (3) ‘Gender equality, disability, and social inclusion (GEDSI) status in the urban area’. The user of the framework must be able to identify the entities that manage the water supply and wastewater systems in the area. This section may include government agencies and private organizations that play important roles in the operation of water supply and wastewater management in the urban area.

Moreover, the user of the framework must also be able to determine the status of the population served by the utilities and entities. In this section, users must also identify the scope of the water sources served in each section of the community and the wastewater influence areas served. Apart from the general population, users may also choose to determine the GEDSI status of the urban area to ensure that the climate resilience assessment also considers socio-economic aspects and vulnerable areas, especially in urban areas where there are wide income disparities.

In parallel, climate stresses that directly and chronically affect the system are carefully enumerated and labeled as ‘Urban area climate stresses’. Makropoulos et al. (2018) emphasized the importance of determining the effect of climate stresses on UWSS to narrow down the type of metrics and adaptation methods applied in the urban area of interest. Under this action, the user of the framework must identify the prevailing effects of climate change on the following aspects, labeled as: (1) ‘Water supply system issues’, (2) ‘Wastewater system issues’, and (3) ‘Gender equality, disability, and social inclusion (GEDSI) water supply and wastewater-related issues’. For ‘water supply system issues’, the user should identify the effects of climate change on both the water quantity and quality received and produced by the system. These effects may include a lack of supply, increased sedimentation in the water source, unexpected water supply interruptions, and related issues. Users of the framework can identify common wastewater issues in urban areas, such as sewer overflows, flooding, and low service coverage, and how climate change may worsen these problems. The user of the framework may also examine the prevalence of ‘Gender equality, disability, and social inclusion (GEDSI) water supply and wastewater-related issues’ within the urban area to assess whether vulnerable groups have equitable access to water supply and wastewater services. By following these initial steps to understand the system, users will be able to determine the most relevant indicators and variables, enabling them to effectively assess and enhance the climate resilience of urban water supply and wastewater systems.

For Stage 2: Building blocks of the resilience assessment, the metrics of resilience assessment are developed by determining established UWSS variables that measure the performance of the system. In determining the variables relevant to each dimension, categories in benchmarking studies of water utilities and wastewater treatment plants were used as references for the variables. The selection of variables and indicators is not limited to only water supply and wastewater utility benchmarking studies but may also include water supply and sanitation indicators that are related to other relevant aspects of the urban area for assessment. After enumerating the variables and their normalization methods, climate-driven metrics are determined based on the variables that are sensitive to meteorological changes and extreme events. Climate-driven metrics are mostly applied in aspects that involve changes in the water source and the presence of flooding and other salient consequences to urban areas during extreme events.

Stage 3: Conceptual resilience assessment framework development involves the development of a conceptual multi-criteria resilience assessment framework by sorting the chosen system performance variables into groups of indicators under each dimension. Indicators for each dimension are defined by the significant properties of variables enumerated in the previous stage. Users can find definitions of each dimension in the supplementary material provided in the article.

Lastly, the named dimensions and categorized indicators undergo validation and prioritization through various methods such as global expert opinion and other established statistical methods to complete Stage 4: Validation and Weightage of metrics and framework of the methodology. In the case study, the AHP shall be used to determine the weight of each dimension and its corresponding indicators. The weights derived from the developed resilience assessment framework shall be used to determine a resilience index for each study area. As other methods to ensure the validity of the framework, users of this methodology can opt to increase the sample size of respondents and/or conduct expert interviews or focus group discussions, especially in communities being served by decentralized urban water and sanitation systems. The case study included a large sample size with global experts from all continents.

The main limitation of this framework is that the methodology was only applied to a highly urbanized city, such as Bangkok, Thailand, where the water supply and sanitation infrastructure systems are heavily regulated and monitored. The majority of the variables used to measure the different dimensions of the study are based on established water utility benchmarking tools that are familiar to potential users and organizations, that are already monitored by water and wastewater utilities in the study area.

The 4-stage methodology in the previous section was used to produce a pilot multi-criteria resilience assessment framework for the areas covered by the centralized water supply and sanitation utilities in the Bangkok Metropolitan Area, Thailand. In determining the conceptual resilience assessment framework, understanding the system required mapping a schematic of the scope for the framework development.

As for the stakeholders of the system, the schematic outlines the relevant MWA branches involved in the climate assessment framework, as well as the list of BMA wastewater treatment plants. As discussed in the Study Area section of this manuscript, the water supply system is managed by MWA, and the wastewater collection and treatment are managed by BMA, with the corresponding branches and influence areas listed in the Figure 3 schematic.

Moreover, based on BMA's data and interviews with pertinent officials, the Din Daeng Wastewater Treatment Facility serves the highest population, with over 1,080,000 people, followed by the Chong Non Si Wastewater Treatment Facility, serving 580,000 people. The Rattanakosin Wastewater Treatment Facility serves the smallest population, with 70,000 people as of April 2025. In terms of water supply, MWA has a comprehensive database of customers for each of the 12 MWA branches located on the east bank of the Chao Phraya River, as listed in Figure 3. The case study shall focus on a top-down approach in selecting the information related to stakeholder management of the system since MWA and BMA have comprehensive information on their service and influence areas.

In this case study, the climate assessment framework would be limited to establishments served by the Chao Phraya River system for MWA branches and those served by combined sewage systems for BMA influence areas. Areas that rely on decentralized water supply and wastewater systems, supplied through groundwater sources and served by smaller wastewater treatment plants, will not be included in the climate assessment framework development. Furthermore, the climate assessment framework for this case study does not include a detailed GEDSI analysis and treats the population served as a single entity. In this regard, GEDSI characterization and decentralized systems may be incorporated into future climate assessment framework developments in Bangkok, Thailand.

As part of understanding the system, the climate stresses and their effects experienced by Bangkok, Thailand were also determined. Bangkok's typical climate condition is characterized by extreme wet and dry weather. Consequently, during the peak of the wet season, Bangkok's metropolis frequently experiences flash floods, high river discharges, and turbidity issues (Deesawasmongkol 2014). Coupled with environmental concerns around the metropolis, there have been incidences where urban flooding has been experienced within key areas of Bangkok. Urban runoff in Bangkok (e.g., storm runoff, solid waste, and untreated domestic sewage) during heavy rainfall events increases pollutant loadings, which results in unacceptable levels of total organic carbon and trihalomethanes in nearby waterways within Bangkok (Hak 2015). On the other hand, during the dry season, Bangkok's water supply is affected by saltwater intrusion due to a lack of upstream flows and rising sea levels, which affects the water supply production of the Bangkhen Water Treatment Plant (Koh et al. 2022). Other issues related to weather changes are the presence of algal mats that cause filter clogging and increased backwashing, dosing of coagulants, and chlorine (Hak 2015).

For Stage 2: Building blocks of the resilience assessment, the metrics to measure the infrastructure system performance and the metrics on climate-driven aspects of water supply and wastewater system were gathered. To provide a comprehensive assessment of the centralized components of Bangkok's water supply and wastewater system, the framework should also include indicators and variables related to evaluating the quality of service of water supply and wastewater utilities. These may include data on water pressure, system-wide water supply interruptions, the quality of water produced by both water treatment and wastewater treatment plants, the number of complaints and feedback received by the utilities, and the number of flooding or sewage overflow incidents in Bangkok, Thailand.

However, a limitation of this top-down approach is that households and communities in lower-income areas, particularly those with limited access to communication devices which are also served by MWA and BMA, may not report their water supply and wastewater issues immediately. As a recommendation for future studies, this limitation may be addressed by incorporating indicators and variables obtained through bottom-up data-gathering approaches. Furthermore, conducting a detailed GEDSI assessment, as outlined in Stage 1 of the methodology, along with the integration of participatory methods and community outreach, is recommended to ensure that the framework reflects the experiences of vulnerable and underrepresented groups in Bangkok.

For the ‘Infrastructure Operations’ (D2) dimension, five (5) indicators contribute to quantifying resilience in terms of infrastructure operations, namely: ‘Facility Utilization’ (D2.1), ‘Facility Maintenance Works’ (D2.2), ‘Maintenance Labor Works’ (D2.3), ‘Infrastructure Flexibility’ (D2.4), and ‘Infrastructure Redundancy’ (D2.5). D2.1 describes the efficiency of utilization in terms of both water quantity and quality of water supply and sanitation facilities in Bangkok, Thailand. Indicators D2.2 and D2.3 describe the frequency and duration of maintenance works in important system infrastructure, respectively. Lastly, D2.4 and D2.5 indicators are groups of variables that measure the infrastructure system's capability of providing alternative operational protocols, by ensuring that facilities are flexible and have a degree of redundancy in operations.

For the ‘Quality of Service’ (D3) dimension, six indicators contribute to quantifying resilience, namely: ‘Water Pressure’ (D3.1), ‘Water Interruptions and Restrictions’ (D3.2), ‘Water Supply and Wastewater Quality’ (D3.3), ‘Complaints and Feedback’ (D3.4), ‘Public Health’ (D3.5), and ‘Flooding and overflows in sewer networks’ (D3.6). D3.1 and D3.2 are both related to the quality of water supply volume delivery to the household, while D3.3 refers to the water quality delivered to customers for water supply and the experience of sewerage and wastewater services of customers. D3.4 pertains to the customer experience of water supply and sanitation services in the urban area, by quantifying the number of complaints and duration of complaints in the urban area. The last two indicators under this dimension are D3.5 which is described by variables that measure the number of water-borne diseases in the area, and D3.6 which describes the flooding and overflows in sewer networks.

The next section shall describe the findings on the validation and determination of the weightage for each dimension in the pilot conceptual framework.

For Stage 4: Validation and Weightage of metrics and framework, validation and determination of weightage for the metrics were done. In this study, validation and weights of dimensions and indicators were done on a third-party basis to provide a less biased perspective on the conceptual resilience assessment framework development for highly urbanized cities. A total of 573 global experts were contacted from literature review contact information and the researchers' university contacts were sent out AHP survey forms through Google Forms from June 2023 to September 2023. The average response rate of the experts who volunteered to participate in the AHP survey among those invited is 23% or 119 completed responses out of 573 invitations, with the highest response rate from Asia of 34% or 66 responses out of 192 invitations. The lowest response rate is from Europe with a percentage of 12% or 19 responses out of 159 invitations. To strengthen AHP results, additional European respondents may be included. The top 5 countries with the most respondents are the Philippines (17 respondents), India (13 respondents), Bangladesh (11 respondents), Thailand (10 respondents), and the United Kingdom (6 respondents). In terms of field of expertise, most of the respondents come from academia (55%), while the rest are industry practitioners (45%, total of other categories). 22% of the responses came from the private sector, which included employees and experts from water utilities in their respective countries. In terms of work experience, 41% of the respondents have worked in their respective fields of expertise for more than 16 years.

Upon gathering the results of the survey, Table 1 shows the summary of the weights of each dimension and its indicators considering all respondents, while Figure 4 gives the summary of the weights of dimension and indicators based on income groups. The consistency ratios of the dimensions and indicator levels are well below 20%, and almost all categories are below 10%, except for the indicators of Water Availability and Urban Waterways Management (D1). In this regard, the AHP analyses resulted in acceptable weights (Saaty 1987). Furthermore, the samples were also grouped based on three different income classes based on the World Bank Income Classification as of the 2024 fiscal year namely: High-Income Countries, Upper Middle-Income Countries, and Lower Middle-Income Countries (World Bank Group 2024b). To further enhance the representativeness of the AHP results, respondents from Europe may be added to include to diversify the pool of experts further.

Based on the results indicated in Table 1, the highest weight among the dimensions is ‘Water Availability and Urban Waterways Management’ (D1) (50.34%), while ‘Infrastructure Operations’ (D2) (25.97%) and ‘Quality of Service’ (D3) (23.70%) have almost equal weights. This is because based on the responses of global experts' opinion in the survey, the resilience of the water supply is highly dependent on the quantity of the water sources and the volume of water the urban area receives. This finding aligns with the key conclusions of the Vision 2030 report, which highlight that resilience assessment frameworks must emphasize that water source sustainability is the most critical component of water supply and sanitation systems, rather than relegating water source availability as a secondary consideration (World Health Organization 2009). Resilience assessment frameworks applied in Water, Sanitation, and Hygiene (WASH) communities in Nepal and Ethiopia also regard the assessment of water sources, such as water table and river flow measurements, as primary indicators of the resilience of water sources to drought (Howard et al. 2021). For the indicators of D1, the highest weight among the indicators is ‘Water Source Availability’ (D1.1) (50.37%), followed by ‘Water and Wastewater Quality’ (D1.2) (30.60%), and the last indicator is ‘Climate Change and Extreme Events’ (D1.3) (19.04%). This prioritization is expected since D1.1 emphasizes the volume of the raw water in the water source and the produced volume for the urban area. On the other hand, indicators such as D1.2 and D1.3 can be remedied through available technology and engineering solutions. The study done by Howard shows that indicators for environmental considerations were needed to ensure that the quality of water sources is deemed suitable for treatment using existing facilities (Howard et al. 2021). For other dimensions such as ‘Infrastructure Operations’ (D2) and ‘Quality of Service’ (D3), the respondents expressed that the quality of service is a result of the consistent and proper maintenance of existing infrastructure. However, high quality of service does not always correlate with effective infrastructure operations, particularly in areas where water sources and urban waterways exhibit less to no significant issues related to water quality or volume.

Based on the results in Figure 7, respondents from Lower Middle-Income Countries give a significantly higher weight to D1 (Lower Middle-Income Countries D1 weight: 58%), compared to High-Income Countries (High-Income Countries D1 weight: 49%). Moreover, High-Income Countries give more importance to D2 (High-Income Countries D2 weight: 28%), compared to other classifications. For D3, there was no significant difference in the weights given for all income classes.

In terms of indicators, respondents from Lower Middle-Income Countries (Lower Middle-Income Countries D1.1 Weight: 51%) have the significantly highest percentage of weight for D1.1, thereby implying that securing adequate water volume and supplying the required water demand is of the highest priority among the other three indicators mentioned. This is in stark contrast to Upper Middle-Income Countries (Upper Middle-Income Countries D1.1 Weight: 42%), where the weight for D1.1 is 9% lower than Lower Middle-Income Countries. Consequently, Upper Middle-Income Countries' weight for D1.3 is the highest among the 3 income classifications with a weight of 25%. For ‘Infrastructure Operations’ (D2), the highest rates are ‘Facility Utilization’ (D2.1) (27.45%) and ‘Facility Maintenance Works’ (D2.2) (23.64%). Based on the AHP survey, experts give more importance to the rate of utilization and maintenance, than ‘Facility Flexibility’ (D2.4) (16.92%) and ‘Facility Redundancy’ (D2.5) (13.82%). Experts' opinions stress the importance of facility utilization since this describes the core function of the infrastructure. In terms of income classes, the top two indicators with the highest percentages are also D2.1 and D2.2, and the lowest percentages are ‘Facility Flexibility’ (D2.4) and ‘Facility Redundancy’ (D2.5) for all income classes. Furthermore, there are no significant differences between the weights among the income classes. Based on the feedback from industry respondents, D2.4 and D2.5 have cost implications and may also need additional space in the facility areas, which may pose an issue in densely populated urban cities. For ‘Quality of Service’ (D3), the highest rates are ‘Water Pressure’ (D3.1) (22.38%), followed by ‘Water Interruptions and Restrictions’ (D3.2) (19.25%) and ‘Water Supply and Wastewater Quality’ (D3.3) (18.18%). Most experts have rated almost equal weights to all factors since all are important in compliance with government and policy standards. In terms of income groups, the top three highest weights are also D3.1, D3.2, and D3.3, respectively. The percentages of the weights do not differ significantly across income groups.

Comparing the results of the AHP survey among income groups, the results indicate that feedback and prioritization are consistent across income levels for both dimensions and indicators. This suggests that the requirements and expectations for resilient urban water and sanitation systems show minimal variation among experts, regardless of the country's income level.

The study initially presented a definition of the resilience of urban water supply and sanitation infrastructure as a system, along with the major components of the urban water cycle. In alignment with this definition and the literature review of various frameworks on resilience in water supply and sanitation infrastructure, three dimensions were developed: ‘Water sources and urban waterways’ (D1), ‘Infrastructure management’ (D2), and ‘Quality of service’ (D3). These dimensions consider not only the sudden impacts of extreme events but also the medium- to long-term implications of climate change. The developed dimensions then served as the basis for a conceptual multi-criteria resilience assessment framework for a target urban area.

In operationalizing this definition of resilience assessment, a step-by-step methodology was presented and applied to the Bangkok Metropolitan Area. The framework development methodology consisted of four stages, namely: (Step 1) ‘Understanding the system’, (Step 2) ‘Building blocks of the resilience assessment’, (Step 3) ‘Conceptual resilience assessment framework development’, and (Step 4) ‘Validation and weightage of metrics and framework’. These stages involved understanding the various system components, examining the implications of climate change and extreme events on the system, narrowing the scope of the resilience assessment within the urban area, and selecting benchmarking variables from reputable water utility studies. These variables were used to form the multi-criteria metrics for assessing resilience and to develop the dimensions, indicators, and variables that comprise the UWSS Index for Resilience, or UWSS Index.

For this study, a multi-criteria conceptual resilience assessment framework was developed for the Bangkok Metropolitan Area, Thailand, to quantify the resilience of its centralized water utility and wastewater systems through an index (i.e., the UWSS Index). The scope of the conceptual framework was limited to areas supplied by the Chao Phraya River Basin, including diverted flows from other sources, and located within combined sewer areas. It excluded a thorough analysis of the GEDSI status, which would better describe informal settlements and other vulnerable communities served by decentralized systems within the Bangkok Metropolitan Area.

Given this limitation, only benchmarking studies for urban water utilities were used to determine the variables for each indicator and the enumerated dimensions. A global expert survey was then conducted to validate the dimensions and indicators and to determine the weight of each dimension and its corresponding indicators. Based on the data gathered, the condition of the water source and its ability to supply the intended volume received the highest priority in the framework, followed by the quality of the water sources.

The conceptual methodology developed may be used as an assessment tool by water utilities and asset managers to identify aspects of UWSS systems that can be enhanced through infrastructure development and maintenance. By applying this methodology, a conceptual resilience assessment framework was established for highly urbanized cities such as Bangkok, Thailand, specifically for areas connected to centralized water utility and sanitation facilities. This framework was tailored to align with the existing infrastructure, data systems, and regulatory management in these centralized systems. Finally, the results of the global expert survey indicated that the weights assigned to each dimension and their corresponding indicators were generally consistent, regardless of the income level of the respondents' countries. Based on the results of the survey, the highest dimension is ‘Water Availability and Urban Waterways Management’ (D1), followed by ‘Infrastructure Operations’ (D2) and ‘Quality of Service’ (D3). Experts from various income levels emphasize the importance of effective river basin management to ensure urban water supplies both upstream and downstream of the intake point. For D1, surveyed experts prioritize ensuring sufficient raw water volume, followed by securing the water quality of the source. Additionally, facility utilization and maintenance are highlighted as the most critical aspect of water supply and wastewater infrastructure operations (D2), as it indicates that the system can provide adequate service to the urban area at any given time. Regarding stakeholder experience as measured by the quality of service (D3), water pressure, interruptions, and restrictions are considered the highest-priority indicators, as they evidently reflect the condition of the primary service provided to the population served.

To improve this conceptual resilience assessment framework, it is recommended that future studies extend the geographical scope to include areas with decentralized water supply and wastewater systems, conduct a thorough GEDSI analysis of the Bangkok Metropolitan Area, and incorporate areas served by the Mae Klong River. Moreover, enhancements to the pilot climate resilience assessment framework may be achieved by integrating variables that require bottom-up data-gathering approaches, particularly for vulnerable and low-income communities within the Bangkok Metropolitan Area.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.