Recent and future exposure of water, sanitation, and hygiene systems to climate-related hazards in Zambia

Efforts to safely manage water occupy center stage in global dialogues about water, sanitation, and hygiene (WASH; UN 2020). However, billions of people still lack access to reliable WASH (Rahut et al. 2022). In total, over 2 billion people lack access to safe drinking water, over 4 billion do not have access to safe sanitation, and basic handwashing facilities remain elusive for ∼3 billion people (WHO 2019). Curtis & Cairncross (2003) contend that reliable access to WASH services has the potential to cut diarrhea-related mortality by 45%. In addition, access to WASH services can significantly reduce time spent on water fetching, thus potentially enhancing school attendance (Belay et al. 2020), food production (Gomez-Zavaglia et al. 2020), and overall quality of livelihoods (Uddin et al. 2020). Global estimates indicate that 500 million menstruating persons lack access to adequate water and facilities for menstrual hygiene management (MHM; World Bank 2022). The availability of WASH, MHM services has also been found to significantly impact school attendance (Chinyama et al. 2019). This is concerning especially considering that millions of girls and women still lack access to MHM in schools across the globe (UNICEF 2022a, 2022b).

Challenges related to WASH access are especially apparent in developing regions such as Sub-Saharan Africa where water resources are increasingly threatened by the increase in demand vis-à-vis rapid population growth, agricultural expansion, and civil unrest (Msangi 2014; Momberg et al. 2020). For example, in the Central African Republic (CAR), WASH developmental pursuits have been hampered by civil unrest, and the country's access to drinking water is at just 37% (UNICEF 2022a, 2022b). As a major consumer of water in Sub-Saharan Africa, agricultural expansion has also hindered progress toward achieving sustainable development goal number 6: water and sanitation for all. For example, in Mozambique, the cultivation of sugar cane consumes 600% more water per ton compared to the global standard. This ineffective use of water can strain the availability of drinking water (Water Footprint Network 2020).

Perhaps one of the most common hindrances to WASH access relates to climate change-induced hazards that are affecting Sub-Saharan Africa in increasingly severe ways. We use ‘hazards’ to mean the occurrence of climate-related physical events that may cause damage and/or loss depending on the level of exposure, i.e., ‘the presence of assets, services, resources, & infrastructure that could be adversely affected if a hazard occurred’ and vulnerability, i.e., a general lack of capacity to cope and adapt (IPCC 2014). Sub-Saharan Africa is one of the most vulnerable regions to climate change and one of the least ready to respond to the impacts of climate-related hazards (Davis & Vincent 2017). The region's vulnerability undermines WASH developmental pursuits by reducing the availability of critical natural resources such as freshwater (Kusangaya et al. 2014). During the 2015/2016 season, climate change-induced drought exacerbated by one of the strongest El Niño events characterized by an unusual warming of the eastern equatorial Pacific Ocean (ECMWF 2017) triggered high-intensity droughts that led to freshwater shortages across much of southern Africa (Action Aid 2020). Similarly, floods have become frequent across the region (Schatz 2008; Dube et al. 2021), damaging WASH and other critical infrastructure (WaterAid 2022). The most recent devastating flood occurrence across the region was triggered by Tropical Cyclone Freddy (TC Freddy; UN 2023) which made landfall in Mozambique, undoing some WASH progress, and taking a toll on healthcare systems by the destruction of critical infrastructure and leaving over 200 people dead in neighboring Malawi (AP 2023). Tropical Cyclone Freddy left thousands of people across southern Africa cut off from shelter, basic food, and clean water.

All these climatic shocks highlight the need for WASH sustainability mechanisms across southern Africa where estimates of WASH access remain fraught with uncertainty. However, empirical research evaluating the impact of climate hazards on WASH systems has been mostly anecdotal. Much research focuses on WASH access (e.g., Bresee et al. 2016; Morgan et al. 2017). The research often aims to narrow the gap between policy and practice. There is very little WASH research that uses cutting-edge climate models to understand climate–WASH interactions. To our knowledge, no peer-reviewed research work exists that links high-resolution climate modeling and WASH systems in countries like Zambia. As such, there is a general lack of understanding of the extent of the impacts of climate-induced hazards on WASH access. Perhaps more concerning, research focusing on future climate hazards and their likely impacts on WASH has mainly been ignored. This gap, if filled, would facilitate practice and pinpoint useful areas that need to be addressed to sustain WASH systems in countries like Zambia.

The overarching goal of the present study is to examine the current and future impacts of climate hazards on WASH access and services in southern Africa, focusing on Zambia. In Zambia, previous research has mainly focused on the success or failure, in hindsight, of WASH programs but has largely ignored linking climate science dimensions to WASH access programs. In this study, we aim to provide a novel overview of climate change-induced hazards on WASH access in Zambia for the past, present, and future. We argue that doing so will provide the much-needed climate science basis for WASH–climate action in Zambia. To achieve this aim, we discuss two independent research questions:

• (i)

  What are the past and present impacts of climate variability on WASH access and services in Zambia?

• (ii)

  What are the projected climate trends in Zambia and how will they likely impact WASH provisioning?

We retrieved household and national WASH access data from the WHO/UNICEF Joint Monitoring Programme on Water supply, Sanitation and Hygiene (JMP; https://washdata.org/ accessed 1 February 2023) for the period 2000–2021. The JMP is internationally recognized for providing up-to-date global estimates of WASH based on data from partners at the country level. The 2022 progress update covering the period 2000–2021 is the most recent version of the dataset. Therefore, the analysis embodied in this study represents the most recent WASH coverage across Zambia. The JMP dataset is widely used in environmental and public health research due to its high-quality data control measures. For example, it has previously been used successfully to analyze the risk of diarrheal diseases and urbanization in Sub-Saharan Africa (Zerbo et al. 2021), and most recently, it was used to examine WASH inequalities in Nigerian Schools (Wada et al. 2022).

While a lot of progress has been made to expand Zambia's climate observations network, access to long-term historical climate data remains difficult and contested which limits the ability to assess satellite precipitation information across the country. To bridge this information gap, previous studies, including the IPCC's latest sixth assessment report (hereafter AR6; Gutiérrez et al. 2021) relied on Global Precipitation Climatology Centre (GPCC) monthly precipitation data from the Physical Science Division of the Earth System Research Laboratory (https://www.esrl.noaa.gov/psd/data/gridded; accessed 28 February 2023). The present study also relied on GPCC data to understand historical variations of precipitation across the country (Sian et al. 2021). GPCC data has a spatial resolution of 0.5° × 0.5° and covers the period 1891–2016.

Simulations from the latest state-of-the-art Coupled Model Intercomparison Project Phase 6 (CMIP6), as used in AR6, were employed to deepen the understanding of extreme precipitation events and the risk they pose to WASH systems across Zambia in the future. Before projections, a rigorous skill assessment of 23 CMIP6 general circulation models (GCMs; Table 1, Sian et al. 2021) was done. For compatibility, only the first-member variations (rli1p1f1 r1: realization index, i1: initialization index, p1: physics index, and f1: forcing index) of each model were used in the assessment. Furthermore, the assessment was done using only the intermediate scenario (SSP2-4.5) which was chosen because it offers the closest representation of current global efforts being implemented to keep emissions of greenhouse gases from escalating (Riahi et al. 2017).

We used descriptive statistics to analyze WASH access across Zambia. Key metrics used include the distribution of WASH coverage at rural, urban, and national levels. Central tendency and variability of the full dataset were also considered.

To quantify future extreme rainfall events across Zambia, we employed a set of internationally recognized core climate indices as proposed by the Climate and Ocean Variability, Predictability, and Change (CLIVAR), the Global Climate Observing System (GCOS), and the United Nations World Meteorological Organization (WMO). While there are 27 core indices (Karl et al. 1999), in this study, we focused on 2 key indices that describe the frequency and intensity of heavy rainfall events and that invariably affect the WASH sector. These indices include (i) heavy rainfall, i.e., R95p – Annual total precipitation when daily rainfall (RR) > 95th percentile and (ii) consecutive dry days (CDDs).

For projections, we divided the future into two time slices herein referred to as ‘the near future’ (2025–2054) and ‘the far future’ (2071–2100). Regarding emission scenarios, this study mainly relies on Shared Socioeconomic Pathways (SSPs) and in particular, the SSP2-4.5 which we repeatedly refer to as ‘the middle road scenario’ throughout the present study. Although we did not examine other scenarios per se, we make a few references to the SSP5-8.5 scenario which we refer to as the ‘business-as-usual scenario’ or the ‘high-end scenario’. A detailed description of all the scenarios is given by the United Nations Economic Commission for Europe: https://unece.org/fileadmin/DAM/energy/se/pdfs/CSE/PATHWAYS/2019/ws_Consult_14_15.May.2019/supp_doc/SSP2_Overview.pdf [Accessed: 25 December 2022].

A positive or negative value of Z_c indicates an upward or downward trend. At the 95% significance level, the null hypothesis of no trend is rejected if Z_c > 1.96; and at the 90% significance level, the null hypothesis of no trend is rejected if Z_c > 1.645 (Mann 1945; Kendall 1948).

Preliminary findings of the climate risk analysis were shared with the government and other stakeholders during a 2-day discussion at Asmara Hotel in Lusaka, Zambia from 18 to 19 April 2023. The goal of the discussion was to first, peer review the climate risk analysis and second, to solicit climate-resilient WASH ideas. Seventeen participants were drawn from the Ministry of Water Development and Sanitation, the National Water Supply and Sanitation Council, the Ministry of Green Economy and Environment, The University of Zambia, The World Bank, UNICEF, and International Non-Governmental Organizations.

Care was taken to ensure that all participants are Water–Energy–Food Ecosystem (WEFE) Nexus experts. We hypothesized that avoiding limiting participants to WASH only and including those from the WEFE Nexus would ensure that the results include as many different ideas and perspectives as possible. While there is no scientific consensus on the exact number of participants required for an effective focus group discussion, 5–50 participants are generally considered adequate (Dworkin 2012). Therefore, 17 participants were considered enough to satisfy the goal of this study.

The discussions were held in the hotel conference room, providing a conducive environment with all participants seated in an oval conference setting. Consent was obtained to record the discussion anonymously for analyses afterward. Participants were first asked to describe the WASH facilities and services their institutions provide or support. We then followed up with open-ended questions while taking every effort to avoid dichotomous ones. Therefore, the specific questions that were asked are as follows: (i) From an institutional perspective, what are the current and projected climate risks to your ability to provide or support the WASH sector in Zambia? (ii) What recommendations can you give to ensure that your institution continues to provide or support the WASH sector in Zambia? (iii) What project ideas can you suggest that support climate resilience and strengthen the provision of WASH services for the identified high-risk areas and their surroundings?

Results further indicate that at the national level, 65% of the population have access to basic drinking water services, 32% remain reliant on unimproved water services, 6% depend on limited service and the remaining 7% depend on surface water (Figure 1).

Results of the sanitation access analysis reveal that, unlike water, safely managed sanitation is accessible to a bigger part of the rural than the urban population. Specifically, 24% of rural dwellers have access to safely managed sanitation while it remains elusive to the urban dwelling populace. Unplanned urban settlements which constitute 70% of urban dwellers are especially characterized by substandard or complete absence of sanitation facilities (Nkonde 2019). Notwithstanding the number of people with access to safely managed sanitation in rural areas, 49% still use unimproved sanitation with 19% being reliant on open defecation (OD). Without the industries that characterize urban areas, OD is the leading cause of environmental contamination in rural areas and its devastating consequences can include bacterial diseases, stunting, morbidity, and mortality (UNICEF 2018).

The observation that more rural dwellers have access to safely managed sanitation than urban dwellers is counterintuitive and challenges the conventional understanding of sanitation access in Zambia. These discrepancies can be attributed to a general lack of data across much of Zambia. Furthermore, even where data are available, sources and methods used to collect it together with the areas covered tend to differ. Overall, the country's population consists of 32% with access to basic sanitation, 20% have limited sanitation, 11% depend on OD, and the largest number, – 37%, use unimproved sanitation.

Regarding hygiene access, results indicate that 62% of rural and 36% of the urban population have no hygiene services. Estimates reveal that 35% of urban and 29% of the rural population has limited service, 29% of the urban population has access to basic services while only 9% of rural dwellers have access to basic hygiene services. Taken together, over half of the population in Zambia remains without access to hygiene services and only 18% have access to basic services. The remainder of the population has access to limited hygiene services, meaning they have a handwashing facility, but lack water or soap.

Given the interlinkages between climate hazards, epidemics, bacterial, and viral diseases, we explored the relational matrix of the occurrence of hazards and the latter. We found that 50% of bacterial diseases across Zambia occur during flood years. The two viral diseases that were classified as disasters occurred in 1982 and 1990 but they did not coincide with the occurrence of any climate hazard. Only one landslide that occurred during the anomalous 2010 flood year was classified as a disaster. Lastly, the one epidemic that was graded as a disaster in the database occurred in 2000 and this coincided with the occurrence of floods and bacterial diseases.

Further analysis revealed that covering 93% of all cases, cholera is the predominant bacterial disease affecting Zambia. Only one case of dengue was reported in Petauke district of Eastern Province in 2001 (Table 2). As expected, being a water-borne disease, the majority (71%) of cholera cases were observed to have started during the rainy season covering the months of October–April/May. 50% of all cholera cases started during the core of the rainy season (December–February; DJF), three cases – equivalent to 21% of all cases started at the onset of the rainy season in October while only one case (7%) was reported to have started toward the end of the rainy season (April/May). These results are consistent with those of Fernández et al. (2009) who studied the influence of temperature and rainfall on the evolution of cholera epidemics in Lusaka and found that all epidemics are seasonal and coincided with the rainy season across Zambia.

It was observed that cholera is linked to only 50% of flood occurrences but is associated with rainy season start dates for over 70% of all cases. This suggests that while rainstorms and floods facilitate and accelerate the transmission of cholera to new areas (Adetoro et al. 2022), these can be reduced through comprehensive water, sanitation, and hygiene development planning ahead of the rainy season (Baltazar et al. 2022). It is important to note that, in addition to addressing climate risk, social systems are indispensable to reducing or eradicating cholera occurrences (Elimian et al. 2020; Gupta & Gupta 2020; Charnley et al. 2022). We use the term ‘social systems’ here to refer to the conditions in which people live and how they influence health disparities. A social system as a determinant of health, therefore, covers behaviors, socioeconomic factors such as income, education, etc., and environmental or physical drivers such as climate and water quality.

In the far future (Figure 4(b)), CDDs are expected to intensify, and negative anomalies are projected to be non-existent. Areas such as Livingstone in the Southern Province, the Chipata region in the Eastern Province, and the Solwezi region in Northwestern Province will experience the largest dryness of up to 12 days per year in both the near and the far future (Figure 4), thus suggesting that dry parts of the country during the middle of the century will get drier toward the end of the century. It should, however, be noted that although these identified areas will experience more CDDs than other parts of the country, the intensity of dryness is expected more over southwestern Zambia due to already generally low rainfall patterns in that part of the country (Laudien et al. 2022).

Drought causes temporal to chronic water shortages that affect the WASH sector. Already, given increased drought conditions, much of the southern African region has in recent years experienced increased incidences of cholera (Trærup et al. 2011; Cambaza et al. 2019). Drought-driven water shortages lead to the use of often poorer quality alternative water sources. If these locations already often have poor hygiene and sanitation services or OD, water-borne diseases can spread rapidly (Joubert 2023). Projected drought-driven disruptions in water access will likely jeopardize the already fragile water and sanitation systems and further weaken generally poor hygiene practices, especially in populated areas (Howard et al. 2016).

A comparative analysis of CDDs and heavy rainfall events shows that the areas that are expected to experience an increase in CDDs will also be characterized by increases in heavy rainfall events. This finding, therefore, points toward the dominance of single-day extreme precipitation events. These single-day extreme precipitation events will likely be enhanced by the projected increases in intensity of tropical cyclones (TCs) making landfall over central and northern Mozambique (Fitchett 2018; Seneviratne et al. 2021). In a nutshell, TCs making landfall in Mozambique often modulate the climate of Zambia by introducing rainstorms and damaging winds.

The observation that single-day extreme wet events will increase in the near future across much of Zambia suggests a higher risk of rainstorms and floods facilitating and accelerating the transmission of water-borne diseases such as cholera to new locations. There is overwhelming evidence from cholera transmission mechanistic models that rainfall is a statistically significant driver of cholera outbreaks through several transmission pathways but mainly by increasing people's exposure to contaminated water, especially when coupled with deteriorating sanitary conditions during extreme rainfall events (Lemaitre et al. 2019; Elimian et al. 2020; Kruger et al. 2022; Wheeler et al. 2023).

A closer look at the future climate risk of the Kitwe and Ndola regions on the Copperbelt, the Kabwe region in Central Province, all of Lusaka Province, the Livingstone region in the Southern Province, and the Chipata region in Eastern Province reveals that by the middle of the century, an increase in water runoff ranging between 50–100% with respect to the 1981–2010 baseline period should be expected (see climateinformation.org; accessed 16 March 2023). Water runoff is a major source of pollutants because as the water runs on any given surface, it carries bacteria and other pollutants to surface water bodies. Poorly built or managed sanitation facilities can also encourage pathogens, bacteria, and other waste to seep into groundwater (EPA 2015). As such the Kitwe and Ndola regions on the Copperbelt, the Kabwe region in Central Province, all of Lusaka Province, the Livingstone region in the Southern Province, and the Chipata region in Eastern Province will be at a higher risk of bacterial diseases, especially cholera in the near future. With 11 out of 18 models agreeing on the potential increase of runoff across the Kitwe and Ndola regions on the Copperbelt, the Kabwe region in Central Province, all of Lusaka Province, the Livingstone region in the Southern Province, and the Chipata region in Eastern Province, the confidence in the projections is high. Similar to the statement made above regarding heavy rainfall events and population, areas with lower populations will have less risk. While several other parts of the country are expected to experience an increase in runoff, the projected population growth across these areas is not as high as in the Kitwe and Ndola regions on the Copperbelt, the Kabwe region in Central Province, all of Lusaka Province, the Livingstone region in the Southern Province, and the Chipata region in Eastern Province, thus minimizing the hazard risk.

The observation that areas such as Livingstone in Southern Province, the Chipata region in Eastern Province, and greater Solwezi in Northwestern Province will experience the largest dryness in both the near and the far future (Figure 4) suggests a higher risk of increased aridity across these areas. Considering that these areas are also projected to experience rapid population growth in the near future (Figure 7), the concentration of the population in these areas, especially the Livingstone region in Southern Province and the Chipata region in Eastern Province will likely lead to an ecosystem imbalance which will create a new challenge of accessing safe drinking water and this will likely trigger conflicts. In a nutshell, population growth has been known to intensely aggravate water demand and strain water supplies which usually leads to community conflicts, e.g., in the middle east where limited freshwater has been plaguing the region for years (Gadain & Libanda 2023). Limited freshwater access is, therefore, widely regarded as a security challenge (UPI 2009).

In the near future, therefore, areas around the Livingstone region in Southern Province and the Chipata region in Eastern Province are projected to be affected by both water scarcity and an increased spread of bacterial diseases such as cholera. This is especially true considering that under limited freshwater availability, food storage is usually associated with degraded hygiene (Kanamaru 2009). Findings embodied herein have high confidence and complement those of the IPCC's latest assessment which documents that the region is expected to suffer from critical dryness beginning at the 1.5 °C global warming level and high temperatures are expected to enhance evapotranspiration from the region's mega-water bodies which will exacerbate aridification (Hoegh-Guldberg et al. 2018).

Results from the focus group discussions (FGDs) show that due to the projected increase in single-day heavy rainfall events in some areas, the development and monitoring of local-scale precipitation thresholds to trigger flood prevention strategies is indispensable. These locations include: Kitwe and Ndola regions on the Copperbelt, the Kabwe region in Central Province, all of Lusaka Province, the Livingstone region in the Southern Province, and the Chipata region in Eastern Province. While it is known that floods invariably damage WASH infrastructure such as sewers and latrines (Milupi et al. 2022) and cause them to overflow, thereby introducing the Vibrio cholerae bacteria into otherwise clean water sources (Jutla et al. 2013; Erickson et al. 2019), no monitoring of precipitation thresholds exists for the identified areas. Hydrographic datasets combining past precipitation amounts, duration, and flood occurrences can aid the development of thresholds and flood return intervals for the identified areas. Thresholds can then be used in tandem with weather and El Niño forecasts to issue WASH-specific early warning information for early action. This is especially important considering that El Niño events increase cholera incidence by 300% in El Niño-sensitive regions such as Zambia (Moore et al. 2017). By extension, improved national and subnational technical capacity to adequately monitor, collect, and forecast the weather and climate at both short- and long-term timescales is crucial as such information can support decision-makers and aid workers to focus cholera prevention efforts on areas forecasted to experience heavy downpours and floods.

Recent evidence shows that the uptake and ownership of climate information by end users can be enhanced if indigenous climate knowledge is blended with contemporary scientific knowledge (Mushimbei & Libanda 2022). For effective cholera prevention and preparation mechanisms, FGD participants recommended renewed interest in dialogues among WASH-related sectors, end users, indigenous climate knowledge experts, and the national weather service. In turn, these dialogues can strengthen institutional arrangements and create a conducive multi-stakeholder environment for data exchange which will in turn improve access to weather-informed health advisories. Furthermore, multi-stakeholder collaboration can enhance access to data required to support project proposals aimed at improving access to climate finance for effective implementation of WASH–climate change policies. This would also help with championing private sector engagement by straightening the misalignment of policies at all levels including legal and regulatory frameworks. Project proposals can include investment in sanitation improvements, especially for highly populated areas with inadequate sanitation and thus at risk of cholera, such as informal settlements of the Kitwe and Ndola regions on the Copperbelt, the Kabwe region in Central Province, all of Lusaka Province, the Livingstone region in the Southern Province, and the Chipata region in Eastern Province. By extension, multi-sectoral approaches can be used to mitigate risks resulting from increased single-day rainfall events and a drier Zambia in the near and far future.

Results further show that poor drainage networks in Zambia's urban areas exacerbate flooding which then triggers the spread of water-borne diseases. A focus on building urban resilience against floods is therefore recommended. As a first step, drainage mapping for every city, especially Lusaka, is strongly recommended. FGD participants highlighted that all drainages need to be interconnected to ensure the effective direction of flood waters to lowlands. Social norms also need to be addressed if the clogging of drains is to be averted. Regarding rural interventions, project ideas should be gender and culturally sensitive. For instance, it is considered taboo for in-laws to use the same toilet in certain cultures; as such, if projects are not gender and culturally sensitive, OD may not be eradicated, and the spread of cholera outbreaks may not be curbed. This finding agrees with that of Bhatt et al. (2019) who documented that OD is usually by compulsion rather than choice.

The immediate impact of drier-than-usual climates on populations is strained access to safe drinking water (UNICEF 2022a, 2022b). The models point to a drier-than-usual Zambia in the near and far future, especially in the Livingstone region in the Southern Province and the Chipata region in the Eastern Province. This unusual dryness will result in protracted droughts leading to dire water shortages, and reduced groundwater levels compounded by increased pumping during drought. The projected enhanced droughts by the middle of the century will lower water levels to critically low levels in some regions. This will in turn make drilling of boreholes more expensive. This price increase will likely occur in the Livingstone region in Southern Province and the Chipata region in Eastern Province. To this end, strategic investment in enhancing water access should be considered a matter of urgency. Deep groundwater mapping across the Livingstone region in Southern Province and the Chipata region in Eastern Province to ascertain where groundwater is available is recommended before any climate change-resilient water resources investments.

Cholera transmission is also closely associated with limited access to reliable sanitation facilities (Wolfe et al. 2018). Although improved sanitation is an expensive proposition because of manifold technological challenges, rapid urbanization points to the need for safe water and improved sanitation access (Mintz et al. 2001; Waldman et al. 2013). Peri-urban unplanned settlements, refugee camps, and areas populated by internally displaced people are usually at higher risk when minimum sanitation needs are not met. Investments in sanitation improvements in the Livingstone region in Southern Province and the Chipata region in Eastern Province are, therefore, recommended. These high-risk areas can also be supported with projects that focus on enhancing artificial recharge and the control of runoff through the establishment of green areas and groundwater recharge wells.

For effective adaptation, FGD participants recommended that findings from this climate assessment should be incorporated into policy to inform decisions about WASH-related climate interventions. By extension, this would facilitate government-supported capacity building on climate assessments to help strengthen the climate rationale of WASH-related resilience initiatives at all levels for both personnel and mandated institutions.

Climate change is undeniably a water, sanitation, and hygiene crisis. However, very little research work has been done to understand the interlinkages between climate change and WASH in Zambia. The present study was designed to develop a solid climate science basis for WASH–climate action in Zambia. Two key findings emerge from the analysis: first, in the near future, the stretch along the Copperbelt–Livingstone railroad from the north to the south of the country is expected to record an increase in single-day heavy rainfall events. As such, bacterial diseases such as cholera outbreaks are expected to increase. While Zambia overall will experience population increases of up to 60 million by the end of the century, rapid increases are especially projected in the Kitwe and Ndola region on the Copperbelt Province, the Kabwe region in Central Province, all of Lusaka Province, and the Livingstone region in Southern Province. These areas are therefore most at risk of cholera outbreaks. Second, models predict a drier Zambia in the near and far future, especially in the Livingstone region in Southern Province and the Chipata region in Eastern Province. This finding suggests a higher risk of increased aridity in these regions. Despite the insights embodied in the present work, there is abundant room for future research. Additional research would be helpful related to groundwater vulnerability mapping to determine available aquifers that can be exploited; storage capacities of water to survive droughts; innovative and durable sanitation facilities that can survive floods; exploration of water-reducing technologies such as low-flow handwashing and toilets that do not depend on water; and more climate-friendly menstrual health and hygiene management products. Furthermore, urgent implementation of measures to enhance national water storage is strongly recommended. These should include a mix of traditional approaches (e.g., rainwater harvesting, dam construction) and nature-based solutions (e.g., restoration of wetlands).

This work was produced as part of UNICEF Zambia's efforts to generate information on climate projections and risks to strengthen the country's rationale for climate-financed projects in the area of resilient WASH services in Zambia. We acknowledge UNICEF/WHO for the WASH datasets used in this study. We also acknowledge the European Centre for Medium-Range Weather Forecasts' Climate Data Store for the models used in this work. We are grateful to the United Nations Population Division for the population projections used in this work. We further acknowledge the Centre for Research on the Epidemiology of Disasters for the impacts of climate variability on WASH access and services data. We thank FGD participants. The editor and reviewers are also appreciated for their comments that further helped to improve this work.

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

The authors declare there is no conflict.