A natural disaster is any calamitous event generated by the effects of naturally, rather than humanly caused, phenomena that result in great loss of life and the destruction of private property and public infrastructure. Its causes may be weather and climate-related (flooding, famine and wildfires due to shifts in precipitation patterns; hurricanes, typhoons, tornadoes and derechos caused by wind); or Earth-driven (Earthquakes and volcanic eruptions). No region of the world is immune from these events; however, risks of particular types of natural disaster differ from one region to another.

The consequences of a natural disaster are similar to those of war or combat: damage to buildings, crops and infrastructure leads to loss of livelihood; lack of food and clean drinking water increases the risk of disease; and, the displaced suffer stress-related problems including PTSD and major depressive disorders. In addition, the financial burdens of a disaster – particularly in developing countries – are enormous.

Natural disasters also increase the vulnerability of people to health risks by destroying or damaging hospitals and community health services. They can also create new opportunities for health risks by providing a breeding ground for vector-borne diseases such as cholera and malaria. However, it is important to remember that a natural disaster does not automatically lead to epidemics, and that the majority of deaths in a disaster are due to trauma rather than from the outbreak of a communicable disease. Moreover, research shows that if the threat of an epidemic does exist after a disaster, it is mainly because of people with pre-existing vulnerabilities such as chronic illnesses.