Climate change that promotes the mobility of humans and animals including vectors and hosts of different diseases is considered a driver of emerging infectious diseases (IPCC, 2014; Woodward et al., 2014; Bongaarts, 2019). It has threatened to undermine public health advances achieved over the last several decades. Concerted global efforts over the past 4 decades have reduced the global burden of malaria but morbidity and mortality associated with other vector borne diseases, especially dengue, remained on the rise, particularly in the global south (World Health Organization, 2012). More recently, the lancet commission on climate change and health 2019 revealed that suitability of disease transmission (malaria and dengue) by mosquito vectors has increased over the past few years (Watts et al., 2019). This deduction by the leading body of public health researchers specialized in climate change and health effects is underpinned by the geographic expansion of disease vectors and subsequently confirmed cases of vector-borne diseases (VBDs) in the high mountain regions of the world including HKH (Bouma et al., 1996; Bi et al., 2013; Dhimal et al., 2015a,b, 2018, 2021; Dhiman et al., 2019). Studies suggest that the increasing temperature and frequency of extreme rainfall events in high mountains of South Asia is now more conducive for the survival and reproduction of disease-carrying vectors (Dhiman et al., 2011; Dhimal et al., 2015b, 2021; Sarkar et al., 2019).

Vector-borne diseases are among the most studied climate sensitive infectious diseases; hence, mechanisms behind their interaction with climatic factors and the consequential risk of infection are well established (Campbell-Lendrum et al., 2015). Epidemic potential of VBD, in general, has been estimated to increase with the increase in temperature (Patz et al., 1998), which holds equally true for the HKH region. Likewise, increased rainfall may affect the reproduction rate of disease vectors in the HKH region. Furthermore, climate change also facilitates the rapid expansion of the host range and microbial capacity to colonize new hosts (Brooks et al., 2019). While the host factors related to the vulnerability of people living in HKH may be comparable to people living in other parts of the globe; the environmental factors such as disproportionate increase in temperature in high mountains, reduced snowfall, extreme weather events such as heavy rainfall, increased agricultural and farming activities in mountain slopes, and increased accessibility and mobility of people are unique to HKH region (Ebi et al., 2007). These changes observed in the HKH region over the last few decades are likely to increase the risk of VBDs transmission in the context of a changing climate (Dhimal et al., 2018).

Climate change is implicated in the geographical expansion of autochthonous cases of VBDs to non-endemics areas of high mountains in Nepal (Dhimal et al., 2015a). The expanded spatial distribution and increased incidence of chikungunya and dengue over the last decades in the HKH region have been associated with climate change (Phuyal et al., 2020; Dhimal et al., 2021). Increasing number of confirmed cases of Japanese encephalitis in Himalayan highlands, which were previously confined to the lower southern plains, has been linked with climate change (Baylis et al., 2016). Likewise, an entomological survey in the higher mountains of central and eastern Nepal reported the presence of dengue vectors Aedes aegypti and A. albopictus, vector of Japanese encephalitis Culex tritrinorinchoes, malaria vectors Anopheles fluviatilis, A. annularis, and A. maculatus complex as well as lymphatic filariasis vector C. quinquefasciatus (Dhimal et al., 2014a, 2015b). Given the establishment of human biting Aedes mosquitos, the HKH region has been identified as a potential threat zone for outbreaks of Zika virus infection (Dhimal et al., 2018). A model-based study projecting the future risk of dengue virus infection in Nepal under different climate scenarios as denoted by Representative Concentration Pathways (RCP 2.6, RCP 6.0, and RCP 8.5) predicts geographic expansion of dengue virus infection hotspot to the higher elevation regions by 2050–2070 (Acharya et al., 2018). Increased cases of malaria with the rise in temperature and increased rainfall has also been reported from highland regions of Bangladesh, Pakistan, Bhutan, Nepal, and India (Bouma et al., 1996; Haque et al., 2010; Dhiman et al., 2011, 2019; Dhimal et al., 2014b; Wangdi et al., 2020), as shown in Table 1. Sarkar et al. (2019) simulated the future implications of climate change on malaria transmission in India and predicted western Himalayan states to be a potential focus for Plasmodium vivax malaria transmission. Different climate scenarios (RCP 2.6, RCP 6.0, and RCP 8.5) anticipate similar geographic expansion of malaria vectors in the southern Highlands of China by 2030–2050 (Ren et al., 2016). A recent review on climate change and infectious diseases from China has also revealed an association between increased temperature and malaria cases in southwestern highland regions of China including Tibet (Yi et al., 2019).

Water- and food-borne diseases are mainly transmitted through consumption of contaminated water and food – as a consequence of shortage of clean drinking water; lack of hygienic practices, and unavailability of proper food storage facilities, all of which are pervasive in the remote areas of HKH. The classical clinical manifestation or outcome of water- and food-borne diseases is acute diarrhea, which remains a leading cause of death among children below age 5 years (Troeger et al., 2017). An increasing body of evidence suggests that transmission and onset of water- and food-borne illness is highly influenced by climate variabilities in temperature, humidity, and rainfall, periodic events like El Nino, and climate-induced disasters like floods (Checkley et al., 2000; Singh et al., 2001; Liu et al., 2017). Given the higher prevalence of childhood diarrhea and a higher mortality rate among the children of rural mountains in South Asia including countries of the HKH region (Reiner et al., 2020), increased prevalence of diarrheal disease among the people living in the HHK region in the context of changing climate is a major concern. All the means and mechanisms of water- and food-borne diseases transmission are plausible in the HKH region that makes this region a hotspot for diarrheal diseases outbreak under the influence of future climate change.

Despite the higher vulnerability, limited evidence is available on the impacts of climate change in water- and food-borne illness in the HKH region due to the lack of health surveillance data available at the local scale. However, some localized studies identified linkages between climate change and water and food borne diseases. For example, Wangdi and Clements (2017) analyzed nationwide diarrheal datasets in Bhutan, spanning a period of 1 decade and reported that 0.6 and 5% increase in risk for diarrheal incidence per every 1°C rise in maximum temperature and 1 mm increase in rainfall, respectively (Table 2). A study from Pakistan reported that increased temperature and climate induced-flooding events had exacerbated water borne diseases such as cholera and infective gastroenteritis in the mountainous province of Baluchistan (Malik et al., 2012).

Likewise, national and subnational level assessments of the impacts of climate change on diarrheal diseases in Nepal reported a greater impact of climate change on diarrheal diseases incidence among the residents of mountain regions compared to lowland (Dhimal et al., 2016). The study reported an overall increased risk of diarrhea (5.05% per 1°C rise in average temperature) for the mountainous regions, compared to non-mountainous parts of the country. Similarly, for a mountainous region of Southern China, climate-induced flooding events are projected to increase the years lived with disability from bacillary dysentery by up to 8% by the 2030 compared to 2010 (Liu et al., 2017). Moors et al. (2013) used regional climate models to project the future burden of waterborne diarrhea in Ganges basin of Northern India and predicted 13.1% increase in diarrhea cases attributable to climate change by the year 2040 in comparison to the late 1990s. So far, the only study published from Afghanistan has reported a positive association between mean daily temperature and nationwide diarrhea incidence, with 0.70 and 4.79% increased risk of diarrhea for every 1°C rise in mean daily temperature and 0.01 unit change in aridity index, respectively (Anwar et al., 2019).

Several biological and physical mechanisms have been proposed to illustrate potential mechanism by which climate change is likely to enhance transmission of water- and food-borne illnesses (Levy et al., 2016; Bhandari et al., 2020a,b). Apart from the general mechanisms common to most geographical regions, a plausible mechanism possibly unique to the HKH region is the contamination of drinking water sources due to the disruptions of sanitary and sewage systems during extreme weather events such as floods resulting from the outburst of glacial lakes (Ebi et al., 2007). Endowed with the world’s tallest mountains and famous trekking routes, the HKH region is a popular tourist destination among mountaineers and trekkers. Climate change is likely to increase the warm days conducive for trekking and mountain expeditions, which in turn may overcrowd the mountains. Open defecation or improper disposal of sludge and excreta during trekking or mountain expedition may contaminate the springs and water sources (Associated Press, 2019), resulting in outbreaks of waterborne diseases. Likewise, increased frequency of travelers in the mountains – in an already compromised ecosystem with limited resources to sustain the resident population – may introduce new strains of entero-pathogens such as Cholera, which carries epidemic potential. Introduction of epidemic strains of entero-pathogens by a foreigner in an already vulnerable ecosystem was previously recorded in Haiti during the aftermath of the 2010 earthquake (Orata et al., 2014).

Diverse policy responses to climate change have been initiated worldwide including in the mountainous regions. Global debates and dialogs weighing the consequences of climate change in these regions were also realized at Sendai Framework for Disaster Risk Reduction 2015 and the Paris Agreement 2015 of the United Nations Framework Convention on Climate Change (Wester et al., 2019). Similarly, climate change and its impact on human livelihood are now an integral part of the development plans and programs of governments in the HKH region (Ahmed et al., 2019). Despite these initiatives, climate change has already impacted food, water, and nutrition security of the region. Due to the considerable variations in agro-ecological and livelihood resources across the HKH region, disproportionate impacts of climate change on these sectors were observed (Hussain et al., 2016; Merrey et al., 2018). Unprecedented climate changes including increased temperature, year-to-year changing precipitation patterns, frequent floods combined with other drivers such as deforestation and forest degradation, and commercialization of productive agriculture lands are deleteriously affecting agriculture and food security in the HKK region (Nautiyal et al., 2007).

The direct impact of climate change on agricultural productivity accompanied by increased risk of vector–borne infectious disease was reported in a household survey conducted in Rakaposhi valley of Gilgit – Baltistan, Pakistan (Bhatta et al., 2019). Ground water extraction to cope with the uncertainties of surface water availability in the HKH region in anticipation of increased energy demand and severe losses to scarce water resources (Rasul and Sharma, 2016). High incidence of food and nutritional insecurity is prevailing in western and far-western mountainous regions of Nepal, Afghanistan, Chin state in Myanmar, Baluchistan province of Pakistan, and Meghalaya state of India. Climate-induced changes like floods, droughts, landslides, livestock diseases, and increased biological invasions including crop pests have led to decreased food production and farm income for the local HKH communities (Hussain et al., 2016; Shrestha and Shrestha, 2019).

The state of food and nutrition security in the HKH region is not promising especially in remote mountain areas owing to a high incidence of natural calamities, physical constraints to better agricultural productivity, poor infrastructure, and high cost of transportation, and limited access to food markets (Huddleston et al., 2003; Ward et al., 2013). In addition, decreased productivity in agriculture with the changing climate exacerbates food insecurity and malnutrition in the region. Evidently, the causes of food security and malnutrition differ in mountains and plains (Rasul et al., 2019). Drought affects livelihoods in the HKH region by engendering food insecurity through reduced water availability for both agriculture and rangeland production (Joshi et al., 2013; Rasul et al., 2014).

In the face of extensive malnutrition, food insecurity and dampened health care systems in the HKH region, no concerted plans are put in place focusing on enhancing food production and increasing household incomes. For example, one third to half of the children below 5 years of age from the HKH region suffer from stunting and wasting. Climate change and deteriorating agro-ecological environment turn up to be the most significant contributing factors toward food and nutrition insecurity in the region (Rasul et al., 2018). For example, almost two-thirds of Baluchistan and the Federally Administered Tribal Areas (FATA) of Pakistan are extremely food insecure by dint of limited income to purchase sufficient food by the local population (Hussain and Routray, 2012). Myriad challenges worsening food security and nutrition in the HKH region encompass debilitated health care systems, unavailability of clean drinking water, insufficient sanitation, unsafe food, limited knowledge of nutrition at household level, and inability to empower women (Rasul et al., 2019). Climate change has further exacerbated the existing food security challenges.

Climate change in the HKH region increases the frequency and magnitude of both “rapid-onset” hazards and “slow-onset” hazards (Eriksson et al., 2008). Floods, landslides, glacial lake outburst floods (GLOFs), flash floods, and debris flows are categorized as “rapid-onset” hazards, while droughts, heat waves, cold spells, and biological and hydrological changes are “slow-onset” hazards. The frequency and magnitude of GLOFs have increased along the region in recent decades, causing large social and economic damages (Eriksson et al., 2008).

Atmospheric warming in the Himalayan region causes glacial retreat and the formation of meltwater lakes, increasing the likelihood of disasters such as GLOFs. GLOFs are not only an environmental threat but also the cause of social and economic hardship for affected populations. The incidence of GLOFs is increasing in the HKH region. For instance, in the past 7 decades, 20 GLOF events have been recorded in the Himalayan region, which have caused the destruction of life and property, infrastructure as well as agricultural lands and forests. A report released by ICIMOD has mapped and classified more than 25,000 glacial lakes in the HKH region, of which 47 have been labeled potentially dangerous GLOF hazards (Bajracharya et al., 2020). Climate-induced heavy rainfall causes floods, landslides and extreme precipitation interrupts power, contaminates water sources, damages roads, and closes health centers all of which affect public health.

Flash floods destroy crops, directly affecting the supply chain of food, water, sanitation, and hygiene. Floods’ impacts are felt differently among gender and affect women disproportionately. For instance, the flood-related mortality was higher for girls (13.1 per 1,000) compared to boys (9.4 per 1,000), and higher for women (6.1 per 1,000) compared to men (4.1 per 1,000) during the severe flood in Sarlahi district in 1993 in Nepal (Pradhan et al., 2007). Moreover, poor and marginalized groups are more vulnerable to climate-induced disasters because of their settlement in river banks, flood plains and far away from major settlements in which mainly rich and socially advantaged groups reside. This in turn delays rescue and support operations during and after such disasters (Gurung and Bisht, 2014). These examples suggest that disasters will have the greatest impact on poor women and marginalized populations.

Hazards such as floods, GLOFs, and landslides have sustained negative impacts on the livelihoods and health of people in the HKH region. Since these disasters cause major damage to property and agricultural lands, people are stripped of their sustenance and source of income. Besides obvious effects of this such as lack of proper food and resources, psychological stress from these events can also have negative impacts on health (Eriksson et al., 2008).

The effects of “slow-onset” disasters, although less conspicuous, are no less devastating than those of “rapid-onset” disasters. Climate change has affected the hydrological cycles, increasing water stresses, water-related illness. In Yunnan province of China, despite the high economic growth in the region in the past 15 years, the rate of water-borne diseases has not declined. Climate change also causes changes in the ecosystem and biodiversity altering people’s diets, causing issues related to nutrition. In Nepal, there is some preliminary evidence that malnutrition in some indigenous groups can be attributed to “diminishing of wild food,” as local flora and fauna are part of their livelihoods (Eriksson et al., 2008).

Climatic change affects people differently according to their socio-cultural, economic and geographical contexts and impacts of climate change are not gender neutral. Although men and women face similar environmental exposures, e.g., ambient air pollution, unsafe water, and noise, many women and small children are exposed to household air pollution at higher levels than men due to their longer working hours around the cook stove (WHO, 2014). It has also been argued that accounting the gender dimensions of climate change adaptation and mitigation would facilitate understanding the root causes of climate change, and to address it in a more sustainable way than is possible with a gender-neutral approach (MacGregor, 2009). Furthermore, climate change vulnerability and adaptive capacity are dynamic in nature, and changes affecting them at one level can have intense and unseen implications at other levels (Pelling, 2010). Hence, failure to integrate gender dimensions for exploring the root causes of vulnerability and finding a sustainable solution might exacerbate rather than reduce injustices, and climate change challenges might remain unaddressed (MacGregor, 2009). The impact of climate change will not be evenly distributed across the geographical regions and socio-economic groups with greater impact among higher vulnerable regions and populations (IPCC, 2007). For instance, a review of 45 case studies from developing and developed countries supported the assumption that climate impacts affect men and women differently, and women tend to suffer more in terms of their assets and well-being (Goh, 2012). Some other literature related to climate change has shown that women will be more vulnerable than men to the effects of climate change because of unequal power relations, limited access to resources (financial, natural, social, and human) and economic opportunities (Denton, 2002; Skutsch, 2002). Some research showed that direct and indirect impacts of climate change and health risks vary for men and women due to their different gender roles (Duncan, 2007).

A study conducted in central Nepal has shown that the prevalence of undernutrition (measured in terms of underweight and stunting) is higher among boys than girls, which was not attributed to any specific reason in the study; however, it suggested that favoritism of boy child which is common in the country might not be significant in the studied community. Additionally, the study found that the education level of mothers seems to be relevant to help reduce the burden of malnutrition (Sarki et al., 2016). Another study from Humla district of northern Nepal (Himalayan region) has shown that the same social and power relations that are governing the local vulnerability dynamics (such as caste, gender, and access to social and political networks), also play vital roles in determining the impact of climate change adaptation policies (Nagoda and Nightingale, 2017). The gender differentiated health impacts of climate change in highland and lowland Nepal is reported (Dhimal, 2018). Women in general, and those living in resource constrained countries in particular, are more vulnerable to the impacts of climate induced disasters (MOHA, 2015).

The impacts of climate change in the forestry and biodiversity sectors directly affect forest dependent households and communities the most, especially the livelihoods of indigenous communities, women, marginalized, and poor people who depend on medicinal herbs and other non-timber forest products for their incomes and livelihoods (MOSTE, 2014; MOPE, 2017). For example, depletion of forest resources would increase the burden on women to gather fuel wood, food, fodder, and medicinal plants (MOSTE, 2014). In Nepal, traditions make women responsible for collecting firewood for cooking, boiling water, and heating rooms. The steep terrain coupled with climate change, which dries up water sources increases the burden and dangers of carrying water, firewood, and fodder, which takes a toll on health (Leduce, 2008, 2009). In addition, indoor smoke from the kitchen affects women and their children more than men, causing respiratory illness (Subha, 1999).

In order to reduce these burdens and improve health conditions as well as reduce greenhouse gases, environmentally friendly technologies such as biogas, improved cooking stoves, and solar cookers need to be introduced in a gender-friendly way. The disruption of ecosystem services such as the availability of safe water, and declines in agricultural productivity also increase the workload of women because the majority of women in the HKH region rely on the agriculture sector, and they are also responsible for fetching water for domestic purposes. For example, in the hills of Sankhuwasabha district in eastern Nepal, the shortage of water is becoming a critical issue, but men tend to qualify the shortage as severe, whereas women tend to qualify the same problem as moderate (ICIMOD, 2009). These differences highlight gendered prioritization since men often consider water shortages for irrigation as a serious problem, while women consider household water access for drinking, cooking food, and sanitation as a serious problem (ICIMOD, 2009). Water shortages disproportionately impose health risks and acute labor burdens on women and girls primarily responsible for collecting and carrying water over long distances across difficult mountain terrain.