Resilience assessment of urban water supply and sanitation systems: a critical review Open Access

Sustainable development goal (SDG) 6 aims to ‘Ensure availability and sustainable management of water and sanitation for all’, and this goal includes the management of urban water cycles worldwide. Due to various and rapid stressors in urban cities, such as population growth, land-use change, and increasing urban water use, urban centers must be prepared for the effects of these stressors aggravated by climate change and extreme events (World Bank Group 2018). Various reports and evidence on the effects of climate change have been identified in water and sanitation infrastructures globally, which have prompted the need to develop resilience and adaptation solutions to climate change (Howard & Bartram 2010; UNDP-UNEP 2011). Therefore, mainstreaming climate change adaptation into continuous policy development, government budgeting, and implementation in various sectors is slowly becoming an important initiative to prepare and counteract its effects in urban centers (Schaar 2008; UNDP-UNEP 2011). To strengthen the clamor for enhancing resilience, the Vision 2030 report served as the initial reference in considering resilience in rural water and sanitation planning and implementation for low- to middle-income countries. The recommendation of the report shows that higher resilience to climate change-induced events is exemplified in water and sanitation systems that give importance to effective management methods (Howard & Bartram 2010). In this regard, there is emphasis on the need to develop programs and assessment frameworks that determine the most suitable climate-resilient management method for a given urban and rural water supply and sanitation system (Howard & Bartram 2010).

Fortunately, resilience and related concepts, such as vulnerability and adaptation, were already common themes in various scholarly works related to climate-resilient assessment and management. The works of Howard et al. (2016), Kohlitz et al. (2017), and Hyde-Smith et al. (2022) provided a thorough review of resilience assessment and climate adaptation in aspects of water and sanitation. Howard et al. (2016) gave a comprehensive summary of the documented impacts of climate change and corresponding adaptation methods in various sectors of water resources systems and recommended developing detailed assessment methods to identify vulnerable areas of water and sanitation infrastructure systems. Kohlitz et al. (2017) discussed various vulnerability and resilience assessment and adaptation studies in Water, Sanitation, and Hygiene (WASH) communities and made a critique of how scholars view resilience and vulnerability concepts based on their adaptation methods. The review defined perspectives of how scholars perceive resilience and the majority of the available literature centered on the quantifiable impact of extreme events to water and sanitation infrastructure, without considering other socio-economic factors that also describe the affected area (Kohlitz et al. 2017). The consequence of this type of assessment is the lack of balance in understanding resilience and vulnerability (Kohlitz et al. 2017). Finally, Hyde-Smith et al. (2022) presented a comprehensive review of how climate change has affected urban sanitation systems. This review emphasized that non-tangible aspects of water and sanitation infrastructure systems, such as operations and maintenance management, are not thoroughly quantified in most resilience studies for sanitation services (Hyde-Smith et al. 2022). Like the two latter studies presented, this review emphasizes further that traditional resilience assessment methods are more focused on measuring tangible damage to infrastructure during extreme events because of its ease in acquiring its data (Howard et al. 2016; Kohlitz et al. 2017; Hyde-Smith et al. 2022). Due to this convenience, other crucial aspects of resilience that can be improved, such as operations management, infrastructure maintenance, and community-based reception, may be overlooked (Hyde-Smith et al. 2022). To address this gap in the literature, there is a need to develop a critical review that explores scholarly work focused on applying resilience assessment frameworks that tackle contextual issues and other non-tangible aspects of resilience. Complimentary to this, there is also a need to explore indicators of resilience in urban water and sanitation that can be attributed to non-tangible aspects of infrastructure management to develop balanced resilience assessment methods.

Therefore, the main objective of this study is to conduct a critical review of resilience assessment frameworks that investigates both traditional and balanced assessments of urban water supply and sanitation systems to climate change. To achieve the main objective, this critical review intends (1) to examine the relevant resilience assessment frameworks in urban water and sanitation infrastructure systems and (2) to determine the most significant indicators used is their respective assessments. The output of this review may be used by policymakers and urban planners in developing resilience assessment frameworks that consider technical and non-technical aspects of the urban water supply and sanitation systems in their respective localities. A limitation of this critical review is that it does not consider the income class of the country where the resilience assessment framework was applied or originated. This limitation may be addressed in future studies and literature reviews.

To meet the main objectives of the study, a critical literature review was performed using the PRISMA checklist to ensure a thorough and organized examination of the literature (Page et al. 2021), summarized in Figure 1 of the study design methodology. A high-level review on the primary topic, ‘Urban water supply and sanitation system resilience assessment,’ was conducted to identify relevant keywords for search engines. The keywords were categorized into three groups: Urban Water Supply System, Sanitation System, and Resilience Assessment Framework. The Urban Water Supply System category included terms like ‘Water Supply’ and ‘Water Utility.’ The Sanitation System category used terms such as ‘Sanitation Infrastructure,’ ‘Wastewater Infrastructure,’ and ‘Sewer.’ For the Resilience Assessment Framework category, the keywords were ‘Resilience Assessment,’ ‘Resilience Management,’ and ‘Resilience Framework.’ These keywords were combined using the ‘OR’ Boolean operator to ensure the inclusion of various journal articles and documents related to any of the categories. Literature was sourced from online databases and websites of regional and global organizations. Initially, 3,059 articles and documents were identified. The Web of Science database was used to gather peer-reviewed journal articles with a total of 2,913 articles. Additional online platforms yielded 139 journal articles, and grey literature from various recognized organizations contributed seven documents.

A two-step screening process was applied to the gathered literature. The first step involved identifying titles containing the keyword ‘resilience.’ Keywords related to urban water supply and sanitation systems were excluded to avoid limiting the literature review and excluding significant studies on resilience assessment. The second step involved filtering abstracts that mentioned keywords like ‘resilience assessment,’ resulting in 219 abstracts from the initial set of 3,059 articles. To determine the eligibility of these 216 articles, abstracts were reviewed to ensure they explicitly discussed aspects related to the resilience assessment of urban water supply and sanitation systems. This review also filtered out duplicate studies, similar or derivative studies by the same authors, and studies lacking focus on resilience assessment. This process narrowed the collection to 29 articles. Among these 29 eligible articles, 26 were peer-reviewed journals related to various aspects of resilience assessment in urban water supply and sanitation systems, and three were grey literature from regional and multilateral organizations.

Traditional resilience assessment frameworks are defined as frameworks that measure the resilience of urban water and sanitation infrastructure to climate-induced events based on quantitative or tangible components of the infrastructure. Traditional resilience assessment frameworks of urban water supply and sanitation systems typically measure changes in well-established metrics such as water quality concentrations of urban water supply and sanitation components, factors related to water quantity or volume, infrastructure operations management, and meteorological factors.

On the other hand, balanced resilience assessment frameworks measure resilience by considering not only the technical status of the urban water and sanitation system, but also its other non-tangible aspects, such as economic, financial, social components, of systems that are also important in daily operations and maintenance. In other similar literature reviews, balanced resilience frameworks are also termed as ‘soft’ infrastructure metrics of the urban water supply and sanitation system (Kohlitz et al. 2017; Hyde-Smith et al. 2022).

To further differentiate between existing frameworks, literature works on balanced assessment frameworks were subdivided into the following two sub-categories: (1) Water Security Assessment Frameworks and (2) Stand-alone Resilience Assessment Frameworks. Water security assessment frameworks are defined as frameworks that include climate resilience as one of the goals of the assessment, while stand-alone resilience assessment frameworks explicitly state that climate resilience is the central goal of the framework.

Resilience assessment frameworks that were classified in this study are summarized in Table 1, while the following sections discuss the details of the conceptualization and implementation of their respective resilience assessment frameworks.

Traditional resilience assessment frameworks are mainly useful in identifying effective technical methodologies in assessing the hard components of urban water and sanitation infrastructures. Most of the traditional assessment frameworks that center on urban water and sanitation systems tackle urban water supply networks and drainage systems (Logan et al. 2021; Nikolopoulos & Makropoulos 2023; Ladino-Moreno & García-Ubaque 2024; Valizadeh et al. 2024). In these frameworks, the methodology usually involves the development of detailed hydraulic models in specific urban areas. In Nikolopoulos and Makropoulos' work, resilience is modeled through stress testing a base hydraulic model and developing typical scenarios of disruption to predict areas for improvement in the water supply network (2023). Considering scenarios, Logan et al. investigated the effect of water outages due to acute climate-induced events in the demand distribution of critical urban areas (2021). Very specific scenarios, such as the relationship between the location and area of evacuation centers to the water supply, were also investigated in this study (Logan et al. 2021). The results of both studies show the locations of areas that are least resilient in terms of water demand. Ladino-Moreno and García-Ubaque tackle the method of quantifying resilience through leak detection techniques in selected areas within Bogota, Colombia (2024). In this study, advanced modeling techniques, such as artificial intelligence, were used to determine the least resilient portions of the urban water supply network (Ladino-Moreno & García-Ubaque 2024).

Other infrastructures such as urban wastewater treatment plants were assessed by Astaraie-Imani et al., where the effect of climate change was modeled by simulating the operations and monitoring key water quality parameters (2012). For drainage systems, the framework by Valizadeh et al. (2024) also includes the development of a hydraulic drainage model, where a resilience index is developed through the evaluation of the failures within the drainage network (2024). In the work by Lawson et al. (2014), a comprehensive evaluation of flood risk was done using an interdisciplinary approach by building a high-level flood model and incorporating management strategies in the assessment. Regional resilience assessment frameworks for flooding use traditional methods, such as water level, to determine the overall resilience of the service area (Lawson et al. 2014).

Aside from urban hydraulic networks, treatment plants, and drainage systems, there are also traditional frameworks that measure the resilience of the water supply sources and related components of the service area (Shrestha et al. 2020; Neupane et al. 2023; Amitaba et al. 2024; Dheyaa et al. 2024). The resilience assessment framework by Neupane et al. (2023) involved determining the resilience of the groundwater sources of four Asian cities namely Bangkok (Thailand), Ho Chi Minh City (Vietnam), Lahore (Pakistan), and Kathmandu Valley (Nepal). In this framework, the change of groundwater levels due to climate change and anthropogenic factors was the main factor in determining the resilience of the water source for all four cities (Neupane et al. 2023). This study determined that less inhabited areas of the urban cities will be more resilient to climate change, due to the decreased activity and water use (Neupane et al. 2023). Shrestha et al. (2020) conducted groundwater modeling and mapped the resilience ratings based on groundwater levels within Kathmandu Valley, Nepal under different climate scenarios (2020). The results of the study show that the northern and southern areas of Kathmandu Valley are highly resilient to climate change, compared to the central portion of the Valley (Shrestha et al. 2020). Amitaba et al. (2024) quantified resilience by projecting dam water levels in existing dam systems within Dodokan Watershed that supply water to the Nusa Tenggara Barat Province, Indonesia. In this study, spillway operations were revised to adhere to the optimized rule curve based on climate scenarios for increased resilience and downstream safety (Amitaba et al. 2024).  Dheyaa et al. (2024) conducted a resilience assessment using changes in precipitation and temperatures within cities of Iraq, namely Baghdad, Wasit, and Maysan. The changes in precipitation are most evident during the months of December and January, prompting a strong impact on flooding of the urban areas (2024).

The primary benefit of assessing resilience solely based on the tangible aspects of water and sanitation infrastructure is that it offers strong technical support for climate adaptation strategies, particularly for those that involve significant costs. Resilience assessment frameworks that are focused on the urban water supply sources, such as groundwater reserves and dam-reservoir systems, usually utilize established hydrologic and hydrodynamic methods and have adequate data to observe climate resilience (Shrestha et al. 2020; Neupane et al. 2023; Amitaba et al. 2024; Dheyaa et al. 2024). Traditional resilience frameworks make use of highly focused indicators that are usually assessed by modeled simulations, coupled with long-term datasets. However, for hydraulic network models in urban areas, the disadvantage lies in developing accurate base models to simulate water supply and sanitary networks because many urban areas in developing countries have difficulty collecting and consolidating data on existing water and sewage networks. In the studies mentioned, the study areas were located in small areas within developed countries to address the lack of accurate as-built drawings and plans of hydraulic networks (Astaraie-Imani et al. 2012; Logan et al. 2021; Nikolopoulos & Makropoulos 2023). Lorenz et al. (2021) assessed the resilience of water distribution networks by examining the topology of the area, to avoid the need for extensive and accurate water network data. Another difficulty for technical frameworks applied in urban areas is the privacy and security concerns of the location (Nikolopoulos & Makropoulos 2022). As-built plans of hydraulic networks are typically not disclosed outside of the utility due to the risk of potential security breaches. In the study of Nikolopoulos & Makropoulos (2022), the actual name of the study area was not disclosed for security purposes. Moreover, usual traditional frameworks on hydraulic networks are more concerned with the structural resilience of pipes and other infrastructure components of the network during natural and man-made disasters such as earthquakes and terrorism (Nikolopoulos & Makropoulos 2022, 2023).

Another drawback of traditional resilience assessment frameworks is the lack of human impact consideration in the operation of water and sanitation infrastructures, especially during periods of extreme events where there is need for human intervention in facilities that are heavily impacted (Hyde-Smith et al. 2022). Traditional frameworks do not also measure the experience of the communities that are directly served by the urban water supply and sanitation systems, especially vulnerable communities greatly affected by extreme events (Asian Development Bank 2016; Hyde-Smith et al. 2022). In this regard, traditional resilience assessments are recommended to be merged with other frameworks that measure resilience through non-technical indicators, especially frameworks that also assess the communities served during extreme climate-induced events. Additionally, it is recommended that resilience assessment frameworks with a technical emphasis should include multiple components of the system rather than focusing solely on a single infrastructure or water source. This method guarantees a more comprehensive and robust resilience evaluation for technical frameworks.

To recognize the role of non-tangible components of urban water and sanitation infrastructure systems, balanced resilience frameworks were also developed. Since the launch of Howard and Bartram's Vision 2030 resilience assessment framework, the concept of resilience has slowly been incorporated into various publications (Werbeloff & Brown 2011; Asian Development Bank 2016; Gain et al. 2016; Assefa et al. 2018; Jensen & Wu 2018; Rickert et al. 2019; Chapagain et al. 2022). In fact, resilience and related indicators have been added as end goals in water security frameworks (Asian Development Bank 2016; Shamsuzzoha et al. 2018; Rickert et al. 2019; Chapagain et al. 2022). For instance, ADB developed a water security framework that included key dimensions and indicators essential for measuring national and regional water security. One dimension focused on resilience to water-related disasters, assessing the effects of climate-induced events, such as droughts, floods, and storm surges, at the country level to recommend risk reduction strategies like the Sendai Framework for Disaster Risk Reduction 2015–2030 (Asian Development Bank 2016). This framework was applied to regions within Asia such as: South Asia, Central and West Asia, the Pacific, South-East Asia, East Asia, and a separate category on developed nations within Asia. The assessment found that countries with advanced economies in Asia are not necessarily always resilient to extreme events, and feedback from vulnerable communities is an important input to assess the country's climate resilience (Asian Development Bank 2016).

A similar multi-criteria water security framework was developed by Chapagain et al. that was tested in five cities, namely Madaba, (Jordan), Islamabad (Pakistan), Jaipur (India), and Hanoi (Vietnam) (2022). In this framework, water-related disasters were one of the resilience-related dimensions used to assess the water security of the five cities. The assessment shows that all cities prioritize water supply and sanitation in their water security plans, but disaster management during extreme events remains a challenge (Chapagain et al. 2022). In Perth and Melbourne, Australia, Werbeloff and Brown assessed its water security by determining the current state of the available water supply infrastructure in the cities (2011). The assessment findings suggest that centralization and dependence on a sole water source contribute to the limited climate resilience of the urban water supply and sanitation systems in both areas (Gain et al. 2016). Jensen and Wu piloted a water security assessment methodology in Singapore and Hong Kong, that developed a framework related to the quality of service of the urban water supply and sanitation in the respective countries (2018). This study focused on developing a methodology that incorporated factors to identify the water sources and other risk assessment factors. Based on the application of the framework, both countries could enhance their resilience by also expanding water source options and strengthening disaster risk management strategies (Jensen & Wu 2018).

On a smaller scale, a drinking water security framework was developed by Shamsuzzoha et al. (2018), which incorporates a water safety plan to increase resilience in service areas of Patuakhali Pourashava Water Supply System, Bangladesh (2018). 100 households participated in the piloting of the water safety plan for disaster risk reduction and limited the study to water quality testing for drinking water (Shamsuzzoha et al. 2018). The study results show that 89% of the service area have major distrust in the quality of water because of the inadequate infrastructure maintenance of the utility, and some parts of the service areas have inadequate water demand during monsoon season (Shamsuzzoha et al. 2018). In Addis Abada, Ethiopia, Assefa et al. (2018) also applied a water security assessment framework to the city, with resilience as one of the primary goals of the assessment. The study evaluated the water supply, sanitation, and hygiene systems of the city, incorporating both technical and non-technical aspects such as the financial performance and staff capacity of the system. The results show that water supply management performed well, but sanitation and hygiene remained vulnerable, particularly during drought periods (Assefa et al. 2018).

For all frameworks that were mentioned, the concept of resilience was included both explicitly (Asian Development Bank 2016) and implicitly (Werbeloff & Brown 2011; Assefa et al. 2018; Shamsuzzoha et al. 2018; Chapagain et al. 2022) as one of the end goals for the water security assessment. Consequently, the emergence of these water security frameworks has paved the way for a wide variety of methods that can also measure resilience (Werbeloff & Brown 2011; Gain et al. 2016; Assefa et al. 2018; Jensen & Wu 2018; Rickert et al. 2019). The case studies that utilized water security frameworks showed the integration of both technical aspects and non-technical aspects of the urban water supply and sanitation systems to start a participatory discussion on climate resilience and adaptation methods (Werbeloff & Brown 2011; Damkjaer & Taylor 2017; Jensen & Wu 2018; Chapagain et al. 2022).

While incorporating resilience in water security frameworks is significant progress in the available literature, there is still a need for developing stand-alone and focused urban water and sanitation infrastructure resilience assessment frameworks to increase the readiness of urban water supply and sanitation systems during climate-induced disasters and events (Howard & Bartram 2010). Resilience assessment frameworks specifically for water supply and sanitation systems started as a means of identifying the inadequacies of current infrastructure and classifying them according to their level of resilience (Howard & Bartram 2010). In the Vision 2030, the framework aimed to predict the effect of climate change in various regions of the world and to identify the weaknesses in common existing rural water and sanitation infrastructure (2010). Furthermore, Vision 2030 developed a system of classifying technologies based on their resilience to climate-induced events (Howard & Bartram 2010).

Apart from identifying the weak points of water and sanitation systems, there is a subsequent need to develop resilience assessment tools to identify the locations and aspects for investment by funding agencies and local governments (UNICEF and Global Water Partnership 2015, 2017; Batalini de Macedo et al. 2023). UNICEF and the Global Water Partnership developed the strategic framework of the WASH Climate Resilient Development in 2015 and then updated in 2017. This framework aims to build awareness and reinforce climate change resiliency in rural WASH services and other community systems which involves understanding the local issues of the community, and then delivering and maintaining technical solutions to increase climate resilience (UNICEF and Global Water Partnership 2017). The resilience framework developed also stressed the importance of including stakeholder management in conceptualizing solutions for resiliency, which is not typically included in traditional frameworks (UNICEF and Global Water Partnership 2017). Another similar framework was developed by Batalini de Macedo et al. (2023), where a multi-layer framework of estimating hazards, vulnerability, and risk exposure of urban areas was used to measure resilience, and developed interventions in terms of adaptation and mitigation planning, public policy, and infrastructure development (2023). Like UNICEF and the Global Water Partnership's work, this resilience assessment framework also focuses on identifying the low resilience of certain areas in terms of both technical and non-technical aspects through risk mapping and assessment to specify areas that must be funded or invested in (2017). Saikia et al.'s framework titled City Water Resilience Approach (CWRA) involves a step-by-step process of understanding the urban water and sanitation system, climate change, and its relationship with other aspects of city planning such as key stakeholders and policy. Saikia et al.'s pilot study areas were at Cape Town (South Africa) and Greater Miami and the Beaches (GM&B) (United States of America). The framework helped these study areas develop water and sanitation planning strategies in incorporating climate resilience in the operation and maintenance of urban water and sanitation infrastructure (Saikia et al. 2022). In both instances, in addition to identifying infrastructure components for enhancement and suitable candidates for investment, governance and overall management of urban water and sanitation systems were recommended aspects for improvement (Saikia et al. 2022).

Fortunately, there are few resilience assessment frameworks that have been developed and are specific to urban water and sanitation infrastructure systems (Heath et al. 2012; United States Environmental Protection Agency 2021; Sharma et al. 2023). Heath et al. (2012) presented a multi-stage framework titled Rapid Climate Adaptation Assessment (RCAA), that aims to give specific climate-proof recommendations on urban water and sanitation systems in several urban areas in African nations such as Lusaka (Zambia), Naivasha (Kenya), and Antananarivo (Madagascar). The multi-step framework focuses on understanding the urban water and sanitation systems to recommend appropriate infrastructure solutions in terms of both its technical and financial aspects based on the local climate (Heath et al. 2012).  Sharma et al. (2023) developed a multi-criteria resilience framework catered to measure urban household water climate resilience, that is focused on asset management and the socio-political atmosphere of households in Jaipur, India. Apart from the lack of proper climate-resilient infrastructure, the framework was able to show that slum areas at the city borders, which have low coverage of urban water and sanitation infrastructure have lower resilience compared to urban poor communities near the city centers (Sharma et al. 2023). Like both frameworks, the United States Environmental Protection Agency also developed an extensive urban water and sanitation resilience framework in 2014 titled the Climate Resilience Evaluation and Awareness Tool (CREAT) for different states and water utilities all over USA, which aimed to be used by water utilities as a guide in improving urban water and sanitation services (United States Environmental Protection Agency 2021). The implementation of CREAT made use of a wide array of tools in climate change projections and water utility profiles to streamline resilience assessment in the country (Environmental Protection Agency 2017; United States Environmental Protection Agency 2021).

One of the key strengths of stand-alone resilience frameworks is the emphasis on establishing a baseline of existing urban water and sanitation systems (Heath et al. 2012; United States Environmental Protection Agency 2021; Sharma et al. 2023). This approach helps identify system gaps across multiple dimensions and incorporates climate model projections to assess the potential impacts of climate change in the areas under study (United States Environmental Protection Agency 2021). In the case of Sharma et al. (2023), the result of the baseline analysis is that there is the need to provide green infrastructure and water-saving fixtures to increase climate resilience in households, while Heath et al. (2012) focused more on identifying damages in medium- to low-income urban areas and corresponding adaptation measures using their baseline data. In establishing baseline scenarios, researchers of the enumerated frameworks also incorporated a baseline state of stakeholder feedback as a key component to the established frameworks. This was determined through constant feedback from focus group discussions and interviews. The interview process provided an integral validation point for the technical solutions recommended in the studies (Heath et al. 2012; Sharma et al. 2023). Furthermore, the focus group discussions ensure that uncertainties and inaccuracies of climate models were greatly pointed out as an impediment to achieving the most appropriate climate-proofing solutions of existing infrastructure (Heath et al. 2012).

However, it was observed that in these urban water and sanitation resilience assessment frameworks, there is neglect in considering the assessment of the water sources that serve the community and the existing urban waterways in the case study areas. In the work by Sharma et al. (2023), no dimension blatantly considered the hydrologic conditions of the water sources and immediate water bodies in the study area and focused on the existence of typical household solutions that can alleviate climate-induced events. In the case of multi-step frameworks such as RCAA Framework and the CREAT Framework, hydrologic conditions were used but localized models, most especially for areas with groundwater as the main water source, were not thoroughly discussed (Heath et al. 2012; United States Environmental Protection Agency 2021). The main recommendation also discussed by the United States Environmental Protection Agency's CREAT Framework is to incorporate future climate projections in the existing hydrologic models to predict extreme events more accurately, and to build climate change awareness (2021). Moreover, existing frameworks also do not thoroughly discuss the detailed effect on the water quality of water sources during climate-induced events, which is also a point for improvement because water quality dictates water treatment costs and consequences on public health (Heath et al. 2012; Sharma et al. 2023).

Another gap in the existing literature is that many major resilience frameworks do not cover the effect of income class on the delivery of ample urban water and sanitation services. Only the studies of Heath et al. (2012) and Sharma et al. (2023) gave an overview of the resilience in different income levels in their respective study areas, by tackling an overall summary of urban poor communities (2012) and by developing index ratings across all income levels tested (2023). In the framework developed by the CREAT Framework, social divisions are not thoroughly addressed because the target users of the framework are the utilities, so data gathering is focused on the financial status of the water utility (United States Environmental Protection Agency 2021). Batalini de Macedo et al.’s (2023) framework in vulnerability is suggested as a strong model for future resilience frameworks to also include in developing geographical models that relate income levels and urban water and sanitation coverage (2023).

Replicability also is a significant challenge in applying resilience assessment frameworks within developing countries, particularly in data-scarce urban areas. In low-income urban informal settlements located in sub-Saharan Africa, there was difficulty in documenting impacts of floods and droughts in the urban water supply and sanitation systems due to the lack of resources for monitoring and maintenance (Heath et al. 2012). Moreover, the hydrologic analyses and scenario testing within localized areas of Africa have more room for improvement due to the lack of hydrologic data (Heath et al. 2012). To address these issues on data in low-income urban settlements, Heath et al.'s approach to gathering data was through seeking community cooperation and validation with key stakeholders that may be adapted as an initial model for future assessments (2012). Furthermore, other indicators from traditional resilience frameworks and water security frameworks may be reviewed to provide more options in making feasible resilience assessment frameworks in data-scarce urban water and sanitation systems, apart from the issues on data security and privacy mentioned in traditional frameworks (Heath et al. 2012; Nikolopoulos & Makropoulos 2023).

To develop effective resilience assessment frameworks, it is important to identify key indicators of resiliency. In this section, an overview of the indicators used to assess the resilience of urban water supply and sanitation systems in the references included in this critical review are summarized. The indicators of resilience in this study are divided into three categories: technical indicators, economic and financial indicators, and stakeholder and governance indicators. The sub-sections below expound on the references where effective indicators for each category are found, while Table 2 shows the summary of the categories and their corresponding references.

Traditional urban water and sanitation systems resilience frameworks define resilience using a limited set of indicators to describe the resilience of the hard components of the systems (Astaraie-Imani et al. 2012; Lawson et al. 2014; Gonzales & Ajami 2015; Shrestha et al. 2020; Lorenz et al. 2021; Nikolopoulos & Makropoulos 2022; Bouziotas et al. 2023; Neupane et al. 2023; Amitaba et al. 2024; Dheyaa et al. 2024; Ladino-Moreno & García-Ubaque 2024; Valizadeh et al. 2024). For urban water supply networks, Gonzales & Ajami (2015) use indicators such as water volume, water demand, and allocated water or water availability within the water supply network to determine resilience indices and describe other resilience-related concepts. The studies developed by Nikolopoulos & Makropoulos (2022) describe the resilience of water networks through conducting stress tests of various scenarios that generate values on the volume of supply to delivery points. A similar study but done on a large scale was developed by Bouziotas et al. (2023) in Delfland in South Holland, Netherlands, which also relates resilience to optimizing the urban water cycle in the study area by determining the water supply at delivery points. Resilience indices in water distribution networks were also developed by Lorenz et al. (2021) by accessing the topology of the area and determining the hydraulic resistance of the area (2021). Indirect indicators to determine the resilience of water network systems were also measured through the lot size of evacuation centers and water demand values in climate-vulnerable areas (Logan et al. 2021).

For urban sanitation, traditional frameworks usually focus on indicators that are related to damages in flood-stricken areas and water quality of wastewater discharges (Astaraie-Imani et al. 2012; Lawson et al. 2014; Valizadeh et al. 2024). In the resilience index framework developed by Lawson et al. (2014), flood levels and inundated areas generated from hydrodynamic models were used as major indicators of resilience in different climate scenarios (2014). Other minor indicators used to measure the resilience of the area due to urban flooding are sediment yield, suspended solids, organic matter, and particle density (Lawson et al. 2014). Astaraie-Imani et al. (2012) quantified the resilience of a sewer network by developing a hydraulic model that simulates the effluent concentration measured by dissolved oxygen and ammonium, using inputs such as population, consumption, and impervious areas (2012). Valizadeh et al. (2024) measure resilience by evaluating the number of drainage nodes or stormwater manholes that have failed during simulated scenarios. The framework presented in this study is more focused on the resilience and effectiveness of pipe networks when tested in different climate scenarios (Valizadeh et al. 2024). For resilience assessment studies that are focused on the water sources, usual indicators are water table level, reservoir yield, and changes on precipitation and temperature (Shrestha et al. 2020; Neupane et al. 2023; Amitaba et al. 2024; Dheyaa et al. 2024).

Another popular metric in measuring resilience, in terms of the technical aspect, is assessing the performance of the existing technologies or complying with a checklist of well-known sets of resilient technologies used in the locality, especially in identifying the resilience of low-income to poor urban communities (Howard & Bartram 2010; Heath et al. 2012; Sharma et al. 2023). In the Vision 2030 Framework developed by Howard and Bartram, the study areas were focused on rural areas, where piped and non-piped sources of water supply for both inland and coastal areas were evaluated (2010). In this study, small rural water pipe networks and tube wells were evaluated to determine if the current technology can adapt to climate-induced effects. In the aspect of sanitation, technologies for on-site and off-site sanitation were evaluated. Factors such as pit latrines and septic tanks, and transport methods to centralized disposal systems were included in the resilience evaluation. With these types of indicators, results show that low-income households in rural areas can adapt very well to climate change impacts due to the flexibility in the design of sanitation systems. On the aspect of water supply, the indicators also show that management styles are a more important consideration in resilience rather than the technology itself (Howard & Bartram 2010). In the urban household resilience assessment framework done by Sharma et al., resilience is also measured by the existence of green infrastructure, rainwater harvesting facilities, and other water conservation methods within the household or community (2023). Indicators also include the installation of household water-saving fixtures such as low-flush toilets, water-saving showerheads, low-water-consuming household habits, and household water reuse methods as indicators of resilience (Sharma et al. 2023).

Economic and finance-related indicators were also used to describe the resilience of an urban water and sanitation infrastructure systems in scholarly and organizational work (Heath et al. 2012; UNICEF and Global Water Partnership 2017; Assefa et al. 2018; Jensen & Wu 2018; Shamsuzzoha et al. 2018; United States Environmental Protection Agency 2021; Saikia et al. 2022; Batalini de Macedo et al. 2023). However, economic and finance-related indicators vary in terms of the perspective of the framework and the use of the framework. In this review, it was observed that the economic and financial indicators used in the various frameworks were categorized into two perspectives: the utility-based perspective and the community-based perspective. For utility-based perspective indicators, the economic and financial indicators describe the financial performance and economic status of the respective urban water and sanitation utility (UNICEF and Global Water Partnership 2017; Jensen & Wu 2018; United States Environmental Protection Agency 2021; Saikia et al. 2022).

The framework of the UNICEF and Global Water Partnership for WASH communities indicates that one of the major steps in assessing resilience is to review national strategies on water and sanitation services (2017). In this multi-step framework, activities that were done to assess resilience were determining budget allocations for the maintenance and implementation of water and sanitation systems, most especially during emergencies (UNICEF and Global Water Partnership 2017). In Saikia et al.'s framework, indicators for resilience also include the existence of effective funding options and financing where the urban water and sanitation management entity prioritizes efficient procurement processes, adequate funding for water resilience projects, and reasonable water tariff systems (2022). In the list of typical water security indicators shown by Jensen and Wu, operating costs, revenue, and water tariffs were used as financial indicators of water and sanitation systems resilience in Singapore and Hong Kong (2018). In the CREAT Framework, financial impacts on the utility due to continuous service interruptions and other losses were also included in the framework (United States Environmental Protection Agency 2021). The financial resilience of the system is also described in terms of various indices related to debt service, operational costs, and total revenue (United States Environmental Protection Agency 2021).

On the other hand, community-based indicators are defined as the economic and financial status of the community members that the urban water and sanitation system serves. The common characteristics of community-based indicators for resilience assessment are usually the income class and capacity of the community members to pay for services and resilient household water technologies (Heath et al. 2012; Assefa et al. 2018; Jensen & Wu 2018; Sharma et al. 2023). Determining the economic and financial status of the communities being served by the utilities can help determine the existing vulnerabilities in terms of acquiring proper service and resilient technology (Heath et al. 2012; Assefa et al. 2018; Sharma et al. 2023).

Another observation in this critical review is that there is a strong recognition of increasing stakeholder engagement and governance indicators in past resilience assessment frameworks of water and sanitation systems. In early resilience assessment frameworks, key stakeholders and government officials were only consulted verbally through focus group discussions on the current climate conditions on the adaptation technologies (Howard & Bartram 2010; Heath et al. 2012). Other latter frameworks also explore the existence of disaster management plans, as an indicator of preparedness in the area (Jensen & Wu 2018; Chapagain et al. 2022). Sharma et al.'s indicators on governance and social aspects are useful metrics on how individual households participate in community disaster preparedness activities. Moreover, the study also includes whether the households have installed metering technologies that can help manage decisions related to water consumption (Sharma et al. 2023). Frameworks that have a comprehensive set of indicators on governance and stakeholder engagement are WASH Climate Resilience Development and the CWRF Framework. In both frameworks, existing stakeholder engagement and governance were thoroughly reviewed through various methods such as document review of government plans and procedures, community risk assessments, focus group discussions, and key stakeholders (UNICEF and Global Water Partnership 2017; Saikia et al. 2022). In the CWRF Framework, however, the number of stakeholder and governance indicators was more extensive than other frameworks in this critical review (Saikia et al. 2022). The framework recognizes indicators and goals such as the existence of strong leadership and community empowerment, strong multi-basin coordination, effective asset management plans, and the economic growth of communities (Saikia et al. 2022).

The usual set of resilience indicators for stakeholder and governance indicate that in past resilience assessment frameworks, resilience in these aspects was measured based on the strength of leadership of the management of the urban water supply and sanitation system. In more recent frameworks, both the leadership and the receiver of the service are assessed for resilience.

To address the literature gaps in urban water and sanitation resilience assessment frameworks, a critical review of selected documents and peer-reviewed journals was done. In this critical review, urban water and sanitation infrastructure systems frameworks were classified into two types, namely: traditional and balanced frameworks. Traditional frameworks that were identified in this review were found to provide a strong justification for the development of major adaptation methods and infrastructure. In this critical review, examples of traditional frameworks presented are resilience assessments of groundwater sources, dam-reservoir systems, meteorological components, and water supply networks located in various urban centers. Based on the critical review, traditional frameworks are not only difficult to execute in regions with data scarcity and security concerns, but also insufficient to describe the other aspects of resilience such as the state of the community being served by the urban water supply and sanitation systems, especially the vulnerable communities in urban centers.

Conversely, the balanced assessment frameworks applied to urban water supply and sanitation systems discussed in this review recommend non-infrastructure-based climate adaptation methods. These include improvements in utility management and the incorporation of feedback from customers served, thereby ensuring greater resiliency in urban water and sanitation systems. However, balanced resilience assessment frameworks may improve by also incorporating the water sources and urban waterways in the assessment that were initially applied in traditional resilience frameworks. Moreover, current stand-alone balance resilience assessments lack focus on vulnerable sectors of society that may be more sensitive to changes in climate. Consequently, frameworks that do have analysis on this aspect have encountered issues on data scarcity due to the lack of investment and maintenance in urban poor communities.

To overcome the shortcomings of current resilience assessment frameworks, it is recommended to combine traditional frameworks, particularly including water source assessments, with balanced frameworks. This integration aims to ensure thorough coverage of all dimensions of urban water supply and sanitation systems resilience. Additionally, for vulnerable communities where data are scarce, assessments must also focus on stakeholder consultation to have accurate information on the state of resilience of urban water supply and sanitation systems in the area.

This critical review also examined the common indicators of various resilience assessment frameworks and categorized them as: technical indicators, economic and financial indicators, and stakeholder and governance-related indicators. The critical review determined the various technical indicators available in all stages and parts of urban water supply and sanitation systems, including the inclusion of different types of available resilient technologies, especially for vulnerable groups within urban areas. In line with this, economic and financial indicators for resilience that were common within frameworks were subdivided into two groups based on the perspective of the utility or the users of the system. The economic and financial indicators outlined in the critical review collectively highlight the community's ability to secure or fund solutions essential for climate resilience. Stakeholder and governance-related indicators were also discussed in this review, and most frameworks emphasized monitoring indicators related to leadership and community engagement when determining the resilience of urban water supply and sanitation systems.

The findings of this critical review can help policymakers and urban planners develop a resilience assessment framework that can incorporate both technical and non-technical aspects of the urban water supply and sanitation systems, emphasizing the need to include water source assessments and climate resilience technologies into the system. Furthermore, the review can also give users a perspective on effective methods in identifying non-technical areas for improvement so that stakeholders can operationalize the recommendations of the resilience assessment framework within their urban water supply and sanitation systems.

A potential research gap for future frameworks is the need to develop resilience assessment tools that specifically address the needs of vulnerable urban communities. Additionally, future critical reviews could explore comparative approaches between high-income and low-income countries, recognizing that income disparities may influence the climate resilience of urban water supply and sanitation systems.

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

The authors declare there is no conflict.