Floods and tropical cyclones (TCs) are two of the most
common and
costliest climate disasters worldwide, yet a consistent evaluation
of their individual and interactive health effects across events and
countries remains lacking. We aimed to quantify the individual and
joint all-cause and cardiopulmonary mortality risks associated with
flood and TC exposure across countries and regions. Daily all-cause,
cardiovascular, and respiratory mortality data between Jan 1, 2000,
and Dec 31, 2019, were obtained from 2049 locations in 69 countries
or territories globally. Historical flood and TC events were sourced
from the Dartmouth Flood Observatory and the International Best Track
Archive for Climate Stewardship, respectively. For each location,
we applied quasi-Poisson regression with distributed lag nonlinear
models to estimate cumulative mortality risks over 14, 30, 60, and
180 days following flood-only, TC-only, and joint flood-TC exposures.
Location-specific estimates were then pooled using multivariate random
effects meta-analysis to derive overall risk patterns. A total of
24.9 million all-cause deaths, 6.9 million cardiovascular deaths,
and 3.4 million respiratory deaths from 114 locations with ≥1
joint exposure day were analyzed. Relative to hazard-free days, TC-only
exposure days were associated with substantially higher and more prolonged
mortality risks than flood-only days. Overall, we observed a 3% (95%
confidence interval [CI]: 0–7%) increase in mortality over
60 days following flood-only days, compared to 19% (8–32%)
for TC-only days. In the modification analysis of flood effects by
TCs (using nonflood days as risk reference), flood days co-occurring
with TCs exhibited considerably higher mortality risks than flood
days without TCs, particularly for cardiovascular deaths at 30 days
following the event (1.9% [95% CI: 0.9–3.0%] versus 0.1% [0.0–0.2%]).
However, additive interactions between flood and TC exposures were
generally not statistically significant. Strong effect modification
was observed for economic development and institutional quality, as
locations having lower GDP per capita, government effectiveness, and
regulatory quality exhibited particularly elevated mortality risks,
especially for mortality related to TC-only exposure days. In the
current study, TC-only exposure days were found to be associated with
greater short-to-medium-term mortality risks than flood-only days,
and floods co-occurring with TCs could exhibit higher mortality risks
than flood-only events, particularly from cardiovascular causes. Strengthening
economic and institutional capacity and directing targeted postevent
clinical support (particularly cardiovascular care) to socioeconomically
and institutionally vulnerable locations may help reduce disaster-related
deaths, especially after TCs.