The recent concurrence of electrical grid failure events
in time
with extreme temperatures is compounding the population health risks
of extreme weather episodes. Here, we combine simulated heat exposure
data during historical heat wave events in three large U.S. cities
to assess the degree to which heat-related mortality and morbidity
change in response to a concurrent electrical grid failure event.
We develop a novel approach to estimating individually experienced
temperature to approximate how personal-level heat exposure changes
on an hourly basis, accounting for both outdoor and building-interior
exposures. We find the concurrence of a multiday blackout event with
heat wave conditions to more than double the estimated rate of heat-related
mortality across all three cities, and to require medical attention
for between 3% (Atlanta) and more than 50% (Phoenix) of the total
urban population in present and future time periods. Our results highlight
the need for enhanced electrical grid resilience and support a more
spatially expansive use of tree canopy and high albedo roofing materials
to lessen heat exposures during compound climate and infrastructure
failure events.