Populations remember: projecting the intergenerational consequences of heat extremes

Extreme heat events cause substantial excess mortality, yet their long-term demographic consequences extend far beyond immediate death counts. Each heatwave creates demographic memory—the cascading effects of lost individuals who would have reproduced, aged, and shaped future population structures. In this work, I will develop a microsimulation framework to quantify how a single extreme heat event reshapes population trajectories over subsequent decades, comparing outcomes with and without the heatwave to isolate its lasting demographic imprint.

I will implement microsimulations using the SOCSIM package in R, which simulates individual life events—births, deaths, migrations—through probabilistic rules applied at monthly time steps. This granular approach captures how mortality shocks propagate through populations in ways that aggregate models cannot.

I will construct synthetic populations for Western European countries affected by the July 2022 heatwave, initializing from the Human Mortality Database and Human Fertility Database. Two parallel projections will be analyzed: one incorporating observed mortality from July 2022 (including heat-attributable excess deaths), and a counterfactual where mortality follows forecasted baseline rates without the heatwave. I will use the Lee-Carter method to project baseline mortality, allowing the observed July 2022 mortality spike to capture the heat events demographic shock.

By the conference, I expect to present proof-of-concept results showing how the two scenarios diverge. Core outputs will include: excess mortality attributable to the July 2022 heatwave, measures of bereavement quantifying how many individuals lost family members due to heat-attributable mortality, and projections comparing population structures with and without this event over subsequent decades.

Focusing on a single extreme heat event establishes methodological foundations while demonstrating that even one event matters demographically. While climate change will bring repeated heat extremes that compound these effects, understanding one events impact provides the baseline for assessing cumulative effects. The difference between the two projected populations quantifies the full demographic burden: not only immediate deaths, but also potential altered age structures, depleted cohorts, and expanded bereavement.