Mortality displacement denotes a temporal or temporary increase in the rate of mortality in a given population, usually attributable to environmental phenomena such as heat waves or cold spells.
During heat waves, for instance, there is usually an excess mortality rate in the population, affecting especially older adults and those who are sick. For some heat waves, however, there has also been observed a decrease in overall mortality during the subsequent weeks after a heat wave. 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".