Large-scale displacement takes place in the context of disaster because the threat or occurrence of hazard onset makes the region of residence of a population uninhabitable, either temporarily or permanently. Contributing to that outcome, the wide array of disaster events is invariably complicated by human institutions and practices that can contribute to large-scale population displacements. Growing trends of socially driven exposure and vulnerability around the world as well as the global intensification and frequency of climate-related hazards have increased both the incidence and the likelihood of large-scale population dislocations in the near future. However, legally binding international and national accords and conventions have not yet been put in place to deal with the serious impacts, and material, health-related, and sociocultural losses and human rights violations that are experienced by the millions of people being swept up in the events and processes of disasters and mass population displacements. Effective policy development is challenged by the increasing complexity of disaster risk and occurrence as well as issues of causation, adequate information, lack of capacity, and legal responsibility. States, international organizations, state and international development and aid agencies must frame, define, and categorize appropriately disaster forced displacement and resettlement to influence effective institutional responses in emergency humanitarian assistance, transitional shelter and care, and durable solutions in managing migration and resettlement if return is not possible. The forms that disaster-associated forced displacements are projected to take and corresponding national responses are explored in the Indian Ocean tsunami of 2004 in Sri Lanka, a massive disaster in a nation riven by civil conflict; Hurricane Katrina of 2005 in the United States, where the scale and nature of displacement bore little relation to hazard intensity; and the 2011 Great East Japan Earthquake, Tsunami, and nuclear exposure incident exemplifying the emerging trend of complex, concatenating, multihazard disasters that bring about large-scale population displacements.
When natural hazards lead to disasters, they can affect people in many ways, including damaging their housing and negatively impacting their livelihoods. Each year, millions of people are injured or killed as a result of disasters. They can also force people out of their homes: In 2020, 30.7 million new internal displacements linked with disasters, mostly storms or floods, were recorded throughout the world. Between 2010 and 2020, disaster displacements were recorded in 198 countries and territories, making the issue truly global. Such displacement can have severe and long-lasting consequences on physical and mental health, often similar to those of conflict-related displacement. Psychosocial trauma and the deterioration of living standards and housing conditions often alter displaced people’s well-being and their ability to maintain healthy lives or obtain treatment and care. People with disabilities or long-term illnesses are particularly vulnerable in displacement, as are children and older people. Depression and anxiety, malnutrition, communicable diseases, and lack of access to sexual and reproductive health are among the most frequent issues for internally displaced people. The health consequences of displacement linked with disasters vary depending on affected people’s pre-existing conditions and sociodemographic characteristics, the duration and severity of their displacement, and the type of support they are able to access. In cases of mass and protracted displacement, the health of people in communities of refuge and the health systems in the areas of origin and refuge can also be affected, with repercussions on the broader society. Although some of these impacts are relatively frequent and should be systematically considered by national and local governments, humanitarian organizations, and aid providers, each situation requires tailored approaches. Information on the health impacts of displacement remains limited, but the body of knowledge is growing as awareness increases on the scale of current and future displacement crises linked with disasters in a changing climate.