Natural Disaster Exposure and Informal Caregiving Burdens: Intensive and Extensive Margin Responses

As natural disasters increase in frequency and severity globally and populations age rapidly, understanding how disasters affect informal care systems becomes critical for policy design in aging societies. This study examines the causal impact of disaster exposure on informal caregiving burdens and caregiver health, exploiting spatial variation in seismic intensity from the 2011 Great East Japan Earthquake. Using difference-in-differences estimation applied to unique longitudinal survey data linked to administrative records, we provide the first empirical evidence distinguishing impacts across the intensive margin (existing caregivers) and extensive margin (new caregivers) — a theoretically important distinction grounded in household production theory that prior disaster-caregiving research has overlooked. We find that a 12 percentage point increase in the proportion of destroyed or damaged houses increases weekly care time by 8.5 hours (45.9% increase) among existing caregivers and raises care provision likelihood by 2.3 percentage points (19.5% increase) among new caregivers. Mental health deteriorates exclusively among new caregivers, with effects concentrated among female and less-educated caregivers. Two key mechanisms drive these effects: disrupted formal at-home care services, with an estimated elasticity of informal-to-formal care substitution near unity, and reduced employment among new caregivers. Our findings reveal substantial hidden welfare costs beyond standard disaster impact assessments and demonstrate that optimal policy responses must account for fundamental differences in household adjustment mechanisms across margins. The results have broad relevance for disaster preparedness planning in aging economies worldwide.