Effectiveness of climate resilient water safety plans in Nepal

Nepal is recognized as one of the countries most vulnerable to climate change and accompanying natural shocks (Dhital et al. 2023). The Department of Hydrology and Metrology has reported that Nepal is already experiencing the impacts of climate change, with an increase of 0.056 °C in annual temperature; analysis from 1975 to 2006 has shown a rise of 1.8 °C (Karki 2004; Synnott 2012; DHM 2017). Climate change represents a major threat to the water supply services in Nepal and evidences of significantly reduced yields in some water sources – for example, yields in the Tanahau district fell by 50% within the period 2004–2014 have been observed (RWSSP-WN 2016). Similarly, in the Thulokhola watershed of the Nuwakot district, in the central part of Nepal, 73.2% of spring sources reduced flow and a further 12.2% had dried up completely, all within the space of a decade (Poudel & Duex 2017). While spring and underground sources being the major water sources for water supply in Nepal, 42,039 water supply schemes (WSS) identified across the country must be evaluated regarding climate resilience (GoN 2018). This study has included the findings about the possibilities of assessing water supply systems for climate change.

A focus on climate change resilience represents a new chapter in Nepalese water governance, with WSSs first being introduced by the fourth national planning document in 1970 (Water Aid 2011). Since 2010, Nepal has significantly improved basic water supply and sanitation coverage, rising from 80.4 to 90% and 43 to 99%, respectively (MoWS 2023). Despite the higher percentage of basic water sanitation and hygiene service coverage, only 68.2% of schemes are capable of delivering water from 42,039 piped WSSs, throughout the year to all taps. Similarly, only 28% of WSSs are fully functional but 36% are in need of minor repairs and 38% need major repairs (NMIP 2014; GoN 2018). The sustainability of water supplies can be enhanced by implementing water safety plans (WSPs) and strengthening the water users committees through better training and support (Davison et al. 2005; WHO 2017; Nguyen et al. 2023).

In 2007, the World Health Organization Nepal World Health Organization (WHO) collaborated with Government of Nepal (GoN) to pilot WSPs in the Kathmandu and Parsa districts to rapidly address the functionality issues in WSSs. This was further scaled up to 40 WSSs throughout the country in 2010 (Khatri & Han 2011). In the case of Nepal, WSPs are designed to figure out the Hazards Analysis and Critical Control Points and are based on a multi-barrier systematic approach for improving and maintaining drinking water quality from catchment to consumers with seven steps of implementation (GoN 2013). From the team formation to the verification of the system's quality, WSP has been introduced as a tool to strengthen the water users committee. In 2017, GoN revised the WSPs to CR-WSP with the inclusion of the climate aspects. The climate resilient water safety plans (CR-WSPs) include four major steps, i.e., (i) WSP team formation, (ii) WSS analysis, (iii) identification of hazard and hazardous events and control measures with improvement and monitoring, and (iv) verification and record-keeping (DWSS 2017). However, the WSP's major drawback is the involvement of professional and trained personnel to continue the WSP functionality.

Globally, 2023 was the warmest on record (WMO 2023) and it is increasingly clear that low- and middle-income countries such as Nepal must act to ensure piped water systems are resilient concerning climate change. Increasing global temperatures are causing water scarcity in different parts of the world, particularly in low- and middle-income countries such as Nepal (Nijhawan et al. 2022). Despite being rich in water resources, overall water security in Nepal is one of the lowest in Asia due to inadequate infrastructure, exposure to water-induced disaster risks, and poor service delivery (Panella et al. 2020). A series of natural disasters has rendered Nepal highly vulnerable to the effects of climate change. These shocks have affected indigenous people, children, and marginalized communities disproportionately (World Bank 2022). As a result, Nepal ranks 125th in the climate vulnerability index, with a high vulnerability score of 0.490 and a low readiness score of 0.361(ND-GAIN 2022), suggesting that substantial investment and innovation are required to improve readiness for action. Accordingly, Nepal urgently needs to identify the tools to safeguard existing piped water systems.

The implementation of a WSP tool developed by the WHO in more than 93 countries has helped to improve the operation and surveillance of microbial contamination (WHO 2017). The how tough is water sanitation and hygiene (HTIW) framework, which has been used to assess community-managed WSSs not practicing any WSPs in Nepal and Ethiopia, has shown that these schemes have low to moderate resilience to climate change (Nijhawan et al. 2022). Similarly, an assessment of urban water utilities in Ethiopia using the HTIW framework showed only moderate resilience (Geremew et al. 2024) with regard to climate change. CR-WSPs have been implemented in limited WSSs in Nepal and the government plans its expansion, there is limited evidence of its effectiveness and the impact of climate change on the WSSs. As such, the main objective of this study is to evaluate the effectiveness of CR-WSP implementation in Nepal and suggest the gaps in WSP implementation in the community-managed WSSs. The associations of six identified domains or indicators from the HTIW framework (Howard et al. 2021), environment, infrastructure, management, community governance and engagement, institutional support, and supply chain are used to evaluate the climate resilience of 10 WSSs. Finally, suggestions for improvement of the WSSs and further assessment were given. The lack of baseline data to compare the presence and absence of WSPs remains the major limitation of this study.

The Department of Water Supply and Sewerage Management (DWSSM) selected 10 WSSs as pilot sites for the implementation of CR-WSP in 2018, with due consideration of geographical locations and the progress of WSP activities. The selected schemes are protected water sources, connected with pipelines for water distribution. Groundwater and spring sources are the major water sources in the selected schemes. Since the objective of this study is to assess the resilience toward climate change in community WSSs practicing CR-WSP, the purposive selection was done after consultation with the DWSSM team. The salient features of the selected scheme are shown in Table 1. The salient features of the selected scheme are shown in Table 1 and Supplementary Table 1.

In Nepal, piped water systems are expanding in both rural and urban areas, and these are in urgent need of assessment. The 10 schemes selected serve more than 480,000 people through protected piped water systems and are managed and owned by their communities (WHO 2021). The selected schemes are the main source of water supply in each service area serving between 750 and 35,000 households (HH) per scheme. Among the studied schemes, 40% of the WSSs studied were completely dependent on mechanized deep borehole/groundwater, while 60% of schemes used both protected springs and groundwater.

Qualitative data were collected using semi-structured questionnaires with the members of the Water Users and Sanitation Committee (WUSC), WSP teams, and CR-WSP committees. Technicians from the Department of Repair and Maintenance, water quality monitoring, and monthly tariff recorders (meter readers) were also involved during the group discussions in each scheme. The developed questionnaires were tied to the HTIW domains outlined above. In total, 10 WUSC and CR-WSP teams were involved in the group discussions where the total number of participants was 128. In addition, secondary data of climate-resilient initiatives from the WUSC, supportive minutes of WSP and WUSC meetings, water sample analysis reports from the different laboratories, repair, and maintenance lists, records of WSP training received by the WUSC, and the financial status of the schemes were collected. The details of data collection methods have been listed in Table 2.

The coordinator from the WSP team, the chairs, treasurers, and secretaries of the WUSCs, and water users from the service area, formed the main participants in the Focus Group Discussion (FGDs). The role of local government in supporting the WSSs, financial support, and training for repair and maintenance, were key focal points in the discussions. Understanding the role of women in any decision-making processes, and particularly that of women from indigenous communities was also prioritized. The FDGs were recorded, and transcribed, and the data were then scored with reference to the HTIW framework.

Observations of the infrastructural components in the scheme were carried out in parallel; the functionality of the infrastructure at sources, reservoirs, control chambers, and leakage on pipelines was recorded in detail. In addition, water sources, storage tanks, and distribution points were inspected using the revised WHO sanitary inspection form (WHO 1997) provided at Supplementary Table 3 and Supplementary Table 4.

The HTIW framework was selected because it has shown to be effective in assessing the climate resilience of community-managed water supplies in Nepal and Ethiopia (Nijhawan et al. 2022; Geremew et al. 2024) and has subsequently been used to assess resilience in multi-village piped water schemes in Ethiopia, rehabilitated water schemes in Mozambique (previously damaged by an Idai cyclone), and is currently or will shortly be deployed in assessing schemes in Indonesia (earthquakes affected), Papua New Guinea (landslides and flood hazards), and Vietnam (flood hazards). The HTIW framework can be applied to rural and small-town water supplies and shows how the findings can be used to prioritize water supplies and identify specific actions to improve resilience.

The six domains adopted from the HTIW framework, i.e., infrastructure, environmental setting (catchment), water and sanitation management, supply chains, community governance and engagement, and institutional support, were scored based on the data collected. Table 3 presents the details of the six domains within the HTIW framework.

The HTIW indicators were scored on a Likert scale from 1 to 5 based on the reported performance of the schemes. Each scheme was awarded a total score ranging from 6 to 30, with the final scores interpreted on the basis of the HTIW scoring index (Table 4).

Communities have taken the lead in managing WSSs in Nepal. However, the challenges of climate change represent a major threat to the sustainability of the water supply system (Howard et al. 2010). Limited knowledge of climate change among those in the management committees needs addressing, and support, in the form of relevant training, represents a priority. However, water resource management is always a complex process though special considerations are paid (Beker & Kansal 2024). But if we consider low- and middle-income countries like Nepal, the schemes assessed are all potentially threatened by climate change, the key issue being that of declining yields. So, adaptation practices (i.e., WSP and CR-WSP) have been implemented in these schemes to evaluate and address threats to supply. The over-extraction of the ground water and a lack of recharging zones for ground aquifer were identified as major concerns in all the studied WSSs.

The progress of WSPs and implementation of CR-WSP across the schemes was discussed during Key Informant Interview (KII) and FGD. The data were then cross-checked with data resulting from the FGD. The WSSs selected for this study were the major sources of drinking water, covering 70% of the service area of the municipality. On assessing the WSSs, using the HTIW framework, the studied schemes were found to have medium to very high resilience. Table 5 shows domain scores in detail for each domain. The majority of schemes (i.e., n = 7) achieved scores that placed them in the high resilience category, with detailed characteristics shared in Supplementary Table 2. The Gajuri and Bardibas schemes were rated as having medium resilience, meaning that substantial improvement across all the domains is needed to make these schemes climate resilient (Table 5).

The infrastructure domain combines data from the field regarding the functionality of scheme components (source to tap) and structures and considers whether they are strong enough to withstand site-specific vulnerabilities. This study considered the maintenance and repair capabilities built into each system. With respect to yields, this study worked to ascertain the levels of related water sources and groundwater level depletion based on data from the management committees. Related to the above, we took into account the availability of alternate water sources, the sustainability of extant sources, and the ability of each scheme to meet the water demand in each service area.

The scoring obtained for the infrastructure domain has a range from 4 to 2, indicating either high or low resilience. Considering water table levels, the degree of sanitary risk, and unsanitary leakages in the transmission network were rationales for determining any resulting scores. The practice of keeping records of yields and groundwater levels was found only in Shankarnagar and Mangadh WSSs. However, the participants in the KIIs and FGDs agreed on the depletion of water yields, especially during peak dry seasons in March and April. Having strong structures observed during the site visit that aligned with the building codes of the GoN was an advantage for schemes that scored highly. Looking at infrastructure indicators, groundwater-based schemes, and spring-fed schemes showed different levels of resilience. The WUSC from Surkhet, Pragatinagar shared that the groundwater sources were found to be less challenged in their operations when compared to spring water sources. The treatment of the water systems in spring sources is more costly compared to the groundwater source, which presents a financial burden. The impact of climate-related events such as flooding and landslides was more troublesome for the schemes with spring sources. Similarly, the Gajuri WSS, with few tap connections, scored poorly due to poorly managed infrastructure. This was unsurprising as earlier research findings had reported WSSs with smaller service areas and fewer tap connections to be more vulnerable and prone to climate change events (WHO 2011; Haider et al. 2014). Similar results have been witnessed in this research too.

The environmental setting or catchment domain was assessed through data relating to the catchment's physiographic and topographical position. In particular, we assessed the vulnerability of sources to contamination from pollutants such as fecal waste, animal excrement, and general flooding. With respect to the environmental setting, among the schemes studied, one scheme was found to be highly resilient, one scheme demonstrated high resilience, five of the schemes demonstrated medium resilience, and three schemes were scored as having low resilience. The detailed rationale for the score has been supported in Supplementary Table 2, that sources safe from human interference, floods, landslides, and natural hazards are ranked higher.

After compiling the data, the Shankarnagar WSS was found to be very highly resilient, while three of the other schemes received low scores (Table 5). The Shankarnagar scheme, which received a score of 5, has never suffered from any depletion of the source and is not at risk of contamination from nearby pit latrines. Its water supply reservoirs are well constructed, and the service area is not at risk of landslides and steep slopes. Importantly, the scheme achieved a low sanitary risk score (<= 2). Conversely, the low-scoring Gajuri, Pachdhara, and Surkhet schemes are situated in flood-prone areas and the transmission pipelines are not well protected. Furthermore, the water sources lie close to, or even below settlements, raising the risk of fecal contamination. For example, high population density, driven by increased urbanization near the source area of the Pachdhara WSS (Figures 2 and 3), is threatening the sustainability of the source.

The water supply management domain was scored based on the performance of the WUSC, financial conditions for procurement, effective maintenance of the system by trained employees, the ability to carry out a timely risk assessment of possible natural hazards, and the inclusion of women in decision-making. Knowledge and understanding of climate change in relation to the WSS were also recorded. We also looked to assess the activeness of the committees, noting the frequency of CR-WSP and WUSC committee meetings. After conducting our data analysis, six of the schemes were ranked as having high resilience (Table 5). Based on our criteria, the management committees were found to be competent in all but the Gajuri and Bardibas schemes. All 10 WUSC participants participated in workshops and received training with respect to climate change and climate resilience, which was provided by the GoN. All the WSSs have also managed to secure more than 33% female participation in their decision-making processes. Mechanical and plumbing training has been provided to employees in the Shankarnagar, Mangadh, and Pragatinagar WSSs. The studied WSSs have received multiple rounds (at least twice a year) of water testing training from the GoN.

During the qualitative assessment, it was found that the committees have only a moderate understanding of climate change, i.e., at least to share the impact of climate change in reference to the examples. The most repeated examples were shifts in rain pattern, severe dryness, decrease in yield, and events of landslides and source flooding. The WUSC of Pachdhara, Surkhet, Bhadgaon, Pragatinagar, and Shankarnagar were found to be actively engaging experts to help with the implementation of climate resilience strategies. The remaining four schemes were scored medium to low resilience considering poor governance procedures, inadequate training, and a basic understanding of climate change based on the findings from the group discussion and record-keeping.

Community governance and engagement indicators were used to assess the levels of participation of water users in the service areas (Howard et al. 2021). Social cohesion and community support with respect to decision-making, particularly during times of stress, were taken into consideration for scoring (Flint et al. 2024). We also looked to assess levels of representation on the committees, for example, levels of representation for marginalized and minority communities. More broadly, we looked at the role played by the committees in disaster preparedness and what action plans might be in place to address water shortages.

Scoring the domain, based on the evidence and findings from FGDs, we ranked the majority (six) schemes as having medium resilience, with the remaining four schemes being found to fall in the high resilience category (Table 5). The lower scores – in Gajuri, Bardibas, Pachdhara, Surkhet, Bhadgaon, and Mangadh WSSs – were the result of intermittent community engagement in decision-making processes, limited communication within the community, and limited representation of marginalized and minority groups within the WUSCs. Community discussions showed the importance of including marginalized and minority groups within the WSSs. Regular interaction with the WUSCs had the added benefit of improving knowledge of climate change among these groups.

With regular support from the community, good levels of social cohesion, strong civic engagement in times of emergency, active roles in decision-making from the communities, and good representation of women and marginalized communities, the Attariya, Lekhnath, Pragatinagar, and Shankarnagar WSSs were scored as being highly resilient. Good record-keeping was evident in the Pragatinagar, Shankarnagar, and Lekhnath WSSs, with all regular meetings minuted by both the WSP and WUSC committees. The Shankarnagar WSP committee had also audited its vulnerability to climate-related disasters. It was also found that the committees in the Attariya, Lekhnath, Pragatinagar, and Shankarnagar WSSs had identified alternative sources in case of emergency.

Support from the local government is important for the smooth operation of a scheme. The institutional support domain is designed to measure the relationship (technical and financial) between water supply management committees and local governmental bodies. Local government support on issues of risk management, procurement, technical support in times of emergency, and training to capacitate the knowledge of climate change, were collected from relevant records and supported by data from the group discussions with the core management committees.

Institutional support was found to be the most promising domain in all the WSSs studied for this study. Most schemes scored in the high category, with only two schemes achieving medium scores (Table 5). The schemes have all received good support from local government bodies, allowing for smooth functioning and operational effectiveness. Both technical and financial support have been recorded in eight of the schemes. In addition, all the WSS have received frequent training from WHO-Nepal to enhance the implementation of CR-WSP. The WSSs with a medium score – Attariya and Gajuri – received only limited support from the local government, and there were delays in procurement due to inadequate finance and the poor formulation of emergency plans.

The supply chain domain is linked to the functionality of the road network, wireless communications, and the availability of markets for spare parts. Easy access to the service area in times of emergency is a must. Roadways and mobile communication need to be accessible year-round; a record of obstructed roadways (due to landslides, flooding, or any other natural hazards) was determined, drawn from either the group discussions or logbooks.

Overall, the schemes visited were found conscious of safeguarding the water sources with their full efforts, However, the constraint of resource persons to understand the depth of climate change and resilient WSS was missing. The WUSC was dedicated to assuring the water quantity rather than quality. The management committee in all 10 WSS were found to be engaged in workshops and seminars to capacitate themselves in climate change and its aspects.

In Shankarnagar WSS, the maximum score, i.e., 25, highlights a need to ‘maintain performance’ to keep the scheme resilient to climate change. The rationale for its high resilient score includes the appointment of laboratory technicians for regular water quality testing, the regular risk assessment of the scheme, regular groundwater monitoring, and distributed water volume calculations using a bulk meter. The CR-WSP committee showed good levels of inclusion and diversity, with women and disadvantaged groups well represented in the decision-making process. Participation in climate change awareness training, regular repair and maintenance training for employees, and good relations with local and state governments were also recorded in the scheme. Safe from landslides and floods, with multiple routes to market and connectivity to the Indian border, stockpiles of spare parts for emergencies, an emergency fund, support from the community when needed (i.e., pipeline expansion, regular tariff payments), protected forest in the source area, and continuous water supply to consumers are the major aspects required to meet the criteria of the HTIW framework for a high resilience score.

Group discussions highlighted that population growth and increased urbanization a major threats to the deep boring in the city area, and the demand for water is increasing every year. The challenges associated with burst pipes have been also reported from the service area.

Since the implementation of the WSPs in Nepal, is still not deployed to all the WSS. The limitations of WSPs started in 2013 have now been revised to CR-WSP since 2017 (DWSS 2017). Thus, CR-WSP could be implemented in the WSSs, to address the issues of water quality and quantity. In 2022, Nepal has revised the drinking water guidelines standard with the provision of compulsory implementation of CR-WSP (DWSSM 2022), which has paved the way for its mandatory implementations in WSSs. As the sub-indicators in the HTIW framework provide the major guidelines for the assessment, this framework will be beneficial to review the CR-WSP in detail.

Among the studied schemes, the supply chain and institutional support domains have been found to have the strongest indicators, with a mode score of 4 across all the schemes. A similar study done using the HTIW framework with respect to water supplies in Nepal and Ethiopia has shown service management, institutional support, and supply chain indicators to have the lowest resilient scores (Nijhawan et al. 2022). The advantage of CR-WSP implementation has been that schemes have developed supply chain and institutional support as core strengths in adapting to the challenges of climate change. However, this has been largely facilitated by direct support from WHO-Nepal and the DWSSM, and schemes will remain vulnerable if this support is removed (Nhaurire et al. 2023).

The implementation of CR-WSP has improved the ability of the WUSCs to identify risks associated with climate change, improve their service, better record extreme events, and strengthen their financial position. This stands in contrast to the status of comparable schemes in Ethiopia, Gaza, and Nepal that did not have WSPs in place (Nijhawan et al. 2022; Nhaurire et al. 2023; Bombade 2024; Geremew et al. 2024). The pilot has demonstrated that sustainable and safe drinking water schemes can be operated and maintained in Nepal.

Although the HTIW framework is sufficient to assess the resilience of schemes to climate change in general terms, the framework cannot fully capture – for example – the impact of potentially extreme future events. Furthermore, some future threats to the schemes will likely lie outside of the domains described within the HTIW framework.

An action-based approach to address the impacts of climate change in WSS should be prioritized, but Nepal has been experiencing significant conflict and debate on the issue of ownership of the water sector, due to the three tiers of federalism (DRCN 2020). Each domain of the HTIW framework is equally important to make a scheme resilient and additional domains can be added in the future. Combined studies undertaken in Nepal, Tanzania, and Bangladesh show infrastructure and management alone cannot make a scheme resilient (Charles et al. 2022).

The rising demand for water from increased populations in all the study areas, together with the effects of growing urbanization, catchment encroachment, and declines in water yields, featured strongly as concerns during the qualitative assessment. These indicators need immediate attention. In addition to the six domains, the total water budget available for future spending and detailed studies of groundwater aquifers can make schemes more resilient.

As per the data record available from the Lekhnath, Bhadgaon, and Gajuri schemes in the mid-hills have witnessed more landslides and related disruptions to their services (Nepal Research 2024) when compared to the schemes that operate on the plains. While in the Terai region, group discussions revealed threats caused by road expansion and urbanization. The ribbon settlements around the sources, especially those that involve deep boring, have increased vulnerability to water contamination. Accordingly, WUSCs have increased their awareness of water quality and have implemented functional water test laboratories to measure temperature, turbidity, pH, electronic conductivity, free residual chlorine, and E. coli. However, people in the relevant communities need more training to better understand climate change and the importance of water quality for their schemes.

The microclimate data for the scheme-operated areas are missing, and this has created a problem with respect to ascertaining the true impact of climate change in these locales (i.e., changes in temperature and precipitation flux). The study relied, instead, on recollections from participants taking part in the study to plug this data gap. As the HTIW framework is a convenient way to assess the resilient status, detailed sub-indicators could enhance the use of this framework.

The DWSSM has identified 42,039 WSSs owned and managed by the community in Nepal, all of which need to adopt the WSP. This represents an opportunity to employ the HTIW framework across the country, so as to create a detailed map of the resilience of WSSs throughout Nepal. This, in turn, could be used to guide policymaking (fine-tuning the framework over time). Nepal has agreed to meet the sustainable development goals where achieving resilient water supply and water security can be part of CR-WSP.

The implementation of the CR-WSP in the scheme has shown that the WUSCs and WSP team are putting their good effort to keep the norms of the CR-WSP. The WSPs have become successful in at least protecting the water sources. Regular monitoring of the water quality and involvement of women in decision-making was found in most of the schemes. This study has also identified CR-WSP as a proactive tool to safeguard water systems from the impacts of climate change. The finding of resilience of protected piped water system with a medium resilient score shows to be consistent with the results from similar studies done in other small water supplies in Nepal and Ethiopia. Most importantly, based on the HTIW framework, this study has allowed for an assessment of the WSSs, allowing for the easy prioritizing of necessary actions. The HTIW framework is sufficient to identify and address local climatic threats, and the resilience scores demonstrate the value of implementing CR-WSP. However, there is always room for improvement. As the supply chain and the institutional support domains are strong across all the studied schemes, the remaining four domains require attention. The improvement can be done at the policy level from the concerned stakeholders with continuous support and encouragement to implement water safety tools. The recent policy from the GoN to implement the WSP in all the WSS with new drinking water guidelines can help in strengthening the WSS. Since the mean resilience scores of the WSSs are in the medium category, the WSSs have confirmed a moderate level of resilience to climate change. The WSS practicing CR-WSP found to be the most effective was the Shankarnagar scheme, and it is categorized as having very high resilience. Safeguarding water is a continuous, longitudinal, and fundamental process, demanding attention from point of source to point of use. Resilience assessments are a way to make water sources more sustainable for the future. This can be achieved if the assessments undertaken can ably define both the minute and major dimensions of water safety. Regular investment, harmonious relations with local bodies, training for WUSCs, and the strengthening of management committees can all help to make the WSSs sustainable and more resilient to climate change. The community-owned WSSs in rural and semi-rural areas have all proved to be well managed, despite often limited resources. The studied schemes can all be strengthened, working on the basis of the HTIW framework. Importantly, the HTIW framework has been shown to be an effective tool with which to measure the climate resilience of piped water systems; a scaled-up assessment, rolled out across the country, would demonstrate the readiness of WSSs in Nepal to face the challenges of the future. As the assessment was done for climate resilience, positive findings and its attribute for adaptation of the schemes have guided to fulfill the voids of sustainable WSS in Nepal and developing countries.

Funding for this research was secured by the University of Bristol from the Quality Related Global Challenge Research Fund [Grant Number: 2019-5073]. Technical support for field visits and data analysis was provided by the Aquatic Ecology Center, Kathmandu University.

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

The authors declare there is no conflict.