Mortality displacement denotes a temporary increase in the mortality rate (number of deaths) in a given population, also known as excess mortality or excess mortality rate. It is usually attributable to environmental phenomena such as heat waves, cold spells, epidemics and pandemics, especially influenza pandemics, famine or war.
During heat waves, for instance, there are often additional deaths observed in the population, affecting especially older adults and those who are sick. After some periods with excess mortality, however, there has also been observed a decrease in overall mortality during the subsequent weeks. Such short-term forward shift in mortality rate is also referred to as harvesting effect. The subsequent, compensatory reduction in mortality suggests that the heat wave had affected especially those whose health is already so compromised that they "would have died in the short term anyway".
Death marches can also lead to a significant mortality displacement, such as in the Expulsion of the Valencian Moriscos in 1609 throughout the Kingdom of Valencia and Spanish-held Algeria, the American Indian Trail of Tears, the Armenian Genocide, and the Bataan death march, wherein the oldest, weakest, and sickest died first.
- The Impact of Heat Waves and Cold Spells on Mortality Rates in the Dutch Population Environmental Health Perspectives Volume 109, Number 5, May 2001