Climate Change: An unfolding public health crisis

Climate change is no longer merely an environmental issue; it is emerging as a profound threat to human health and well-being. In this post, Chandra, Sen Gupta, and Zheng discuss the diverse and complex pathways through which climate change affects health. They contend that by investing in infrastructure, empowering vulnerable populations, and implementing evidence-based policies, we can mitigate the health risks posed by a changing climate.

According to the World Health Organization, 50% of the global population resides in areas highly susceptible to climate change, and between 2030 and 2050, climate change is expected to result in an additional 250,000 deaths annually. Other reports by the World Economic Forum and Oliver Wyman present an even more disconsolate scenario, highlighting an additional 14.5 million deaths, US$12.5 trillion in economic losses, and US$1.1 trillion in extra costs to healthcare systems by 2050. From the spread of infectious diseases to respiratory ailments, heat-related stress, food insecurity, and mental health challenges, the pathways through which climate change affects health are diverse and complex. In this post, we discuss insights from a new report by the Asian Infrastructure Investment Bank (AIIB), on the myriad ways in which climate change affects planetary health.

Rise of water- and vector-borne infectious diseases

Extreme rainfall and floods are key events through which climate change accelerates the spread of water- and vector-borne diseases (WVBD) which have a deleterious impact on human health. Excessive rainfall or flooding can cause an overflow of sewage and damage to water and sanitation facilities, resulting in the consumption of contaminated water and the prevalence of diseases like diarrhoea, cholera, typhoid, and leptospirosis. Rising global temperatures affect both surface water and groundwater quality by increasing the concentration of contaminants in water sources due to greater evaporation.

In Indonesia, the number of flood-related disasters surged from 492 in 2008 to 1,299 in 2023, exposing millions to water-borne diseases. As per the AIIB report, health risks significantly increased after a flood event. The probability of sick visits to healthcare facilities in flood-affected regencies is 0.2% higher compared to regencies that did not experience a flood. Similarly, the probability of contracting water-borne diseases post-floods is 0.02% higher in those regencies. With the average direct cost of treating water-borne disease being around US$100 per case, in a city with a population of one million, the direct cost would be around US$20,000 per flood event. In 2022, floods impacted 405 regencies, home to 225 million people, which is estimated to have resulted in 289,093 additional cases of water-borne disease – leading to a direct cost of US$28.7 million. The inclusion of indirect effects such as loss of productivity, mortality, and other long-term impacts would entail a much higher cost.

Similarly, in Sri Lanka, the incidence of leptospirosis in flood-affected districts is four times higher as compared to districts that did not experience floods (Figure 1). Although leptospirosis is less frequently reported, quarterly household data indicate that a one-centimetre increase in rainfall is associated with 0.04 additional cases.

Figure 1. Incidence of leptospirosis and dengue in Sri Lanka

Source: Estimates by AIIB staff.

By exacerbating warmer temperatures and altering precipitation patterns, climate change also raises the survival, replication, and virulence of pathogen and disease vectors such as mosquitoes and ticks. This facilitates the spread of vector-borne diseases like malaria, dengue fever, and Lyme disease to new regions. Studies show that malaria and dengue fever cases are rising in tandem with changing climatic conditions (Clarke and Berry 2012). Flooding compounds these challenges, as stagnant water left in the aftermath of floods becomes breeding ground for mosquitoes, escalating the prevalence of vector-borne diseases.

In Sri Lanka, districts affected by floods report 2.5 times more dengue cases relative to unaffected areas. Granular household data indicate that a one-centimetre increase in rainfall is associated with three additional dengue cases (Figure 1).

Climate change is jeopardising children’s fundamental right to health and well-being in India

Children under five are particularly vulnerable to WVBDs as their immune systems are not fully developed, they have less access to safe water and sanitation, and they may not receive timely treatment. According to the United Nations Inter-Agency Group for Child Mortality Estimation (2019), diarrhoea and malaria account for 8% and 5% of child deaths, respectively. Climate change, by reducing the quality of surface water and groundwater and increasing the exposure to disaster events, is likely to influence the prevalence of these diseases among children.

Using data from the most recent National Family Health Survey, conducted between 2019 and 2021, we evaluate a range of factors that may have a bearing on the prevalence of malaria and diarrhoea among children in India (Figure 2). The likelihood of contracting these diseases depends on various factors at the individual, household, and community levels. Girls have lower chances of contracting malaria or diarrhoea compared to boys.Age also plays an important role. One-year-olds exhibit a higher likelihood of being infected with malaria than infants, but older children are progressively less vulnerable to both malaria and diarrhoea. Certain household factors also have an effect: For example, children of educated mothers have lower odds of contracting malaria compared to those of uneducated mothers, while households with better hand hygiene tend to be less prone to diarrhoea (Figure 3). Unsurprisingly, children from wealthier households show a lower likelihood of contracting malaria and diarrhoea.

Figure 2. Key drivers of malaria prevalence

Source: Estimates by AIIB staff.

Note: WQI = Water Quality Index.

Figure 3. Key drivers of diarrhoea prevalence

Source: Estimates by AIIB staff.

Water quality also affects the prevalence of diarrhoea. Children living in areas with unsuitable groundwater quality have 25.4% higher odds of malaria compared to those in areas with good groundwater. A factor mitigating the adverse impact of water quality on these diseases could be the sharp increase in the proportion of the population having access to improved water. According to the World Bank, 94% of the population in India has access to improved sources of drinking water.

Exposure to natural disasters is also associated with a higher likelihood of both diarrhoea and malaria. For example, households in districts with moderate exposure to disasters have a 44.8% higher likelihood of contracting malaria compared to those in low-exposure districts. Similarly, households in districts with high exposure to disasters are 20.4% more likely to be infected with malaria and 32.4% more likely to contract diarrhoea. A perplexing fact is the relatively higher odds of contracting malaria in districts with moderate exposure to disasters compared to those with high exposure. This could be because high-exposure districts, over time, may have developed better disaster preparations and resilience in comparison to moderate-exposure districts. These observations need further exploration.

Solutions and call to action

While the challenges posed by climate change to public health are immense, solutions exist. Coordinated action, robust policies, and targeted investments within and outside the healthcare system can mitigate these health risks. Some policy options include:

Developing robust and climate-resilient health systems: Investments in public health systems and preparedness are essential to safeguard communities. Expanding healthcare facilities, especially in rural and remote areas, ensures better access to medical services for vulnerable populations. Upgrading primary healthcare networks to handle current needs and future challenges will provide essential support in addressing health risks intensified by climate change. Establishing infectious disease control units in susceptible areas will ensure prompt diagnosis and treatment. Incorporating climate-resilient designs in healthcare infrastructure – such as elevated structures for flood protection, reinforced roofs, passive cooling systems, solar-powered healthcare facilities, and mobile or modular clinics – can help prepare the healthcare system for the future and reduce mortality and morbidity during disasters.

Improving connectivity: Enhanced climate-resilient road infrastructure – such as roads with improved drainage and reinforced embankments, landslide- and erosion-resistant roads and elevated roads and bridges – can significantly reduce travel time to healthcare facilities and improve access to markets and essential services. For instance, India’s rural roads programme has increased the utilisation of reproductive health services and institutional deliveries, particularly in disaster-prone areas.

Gender-responsive disaster preparedness: Women are disproportionately exposed to WVBD due to rigid gender norms (such as bearing the primary responsibility of fetching water for household activities), institutional factors (unequal access to medical care and transportation) and occupation choices (water-intensive sectors such as farming, animal husbandry, household work, etc.). Addressing disparities in resource access and decision-making will help to better protect women during climate-related disasters.

Climate change and health are deeply intertwined. From infectious diseases to mental health challenges, the pathways through which climate change impacts public health are diverse and urgent. By investing in infrastructure, empowering vulnerable populations, and implementing evidence-based policies, we can mitigate the health risks posed by a changing climate. The time to act is now. Together, we can secure a healthier and more resilient future for all.

This article is adapted from an excerpt from Chapter 3: In Deep Water—Climate Change Impacts on Water Systems and Human Health of the report Asian Infrastructure Finance 2025: Infrastructure for Planetary Health.

Disclaimer: The contents of this work are the authors’ own and do not necessarily represent the views or policies of AIIB, its Board of Directors or its Members. The contents also do not necessarily reflect the opinions, positions, or policies of any institutions, organisations, or entities with which the authors may be affiliated.