Impact of extreme rainstorm-induced flooding on emergency healthcare demands in a mountainous district: a multi-group interrupted time-series analysis.

Floods have severe impacts on human health and emergency healthcare systems; however, research on their short-term acute health effects remains insufficient, particularly in vulnerable mountainous regions. The severe floods that occurred in Beijing from July 29 to August 2, 2023, had a substantial significant impact on remote mountainous districts. Utilizing daily emergency department (ED) visit data from a hospital in these remote areas, this study employed a difference-in-differences interrupted time series design to compare the 2023 disaster period with the corresponding periods in 2024 and 2025. We assessed temporal trends in all-cause ED visits, as well as cause-specific visits for cardiovascular disease (CVD), respiratory diseases, and physical trauma, across the acute blockade, and short-term recovery phases. During the acute blockade phase, all-cause ED visits (relative risk [RR] = 0.74, 95% confidence interval [CI]: 0.58-0.96) and CVD visits (RR = 0.50, 95% CI: 0.28-0.91) exhibited significant immediate declines. This reduction may reflect decreased healthcare accessibility resulting from physical isolation caused by extreme rainfall and road disruptions. Moreover, the daily slope of CVD visits showed an increasing trend (RR = 1.26, 95% CI: 1.04-1.54). Upon entering the short-term recovery phase, there was an immediate compensatory surge in all-cause ED visits (RR = 1.28, 95% CI: 1.13-1.44), particularly in visits for physical trauma (RR = 2.23, 95% CI: 1.82-2.75). This rebound was primarily driven by males and adults aged 18-64 years. These findings suggest that acute physical blockades in mountainous regions may temporarily suppress healthcare utilization by limiting access to emergency services, followed by a substantial delayed compensatory surge in ED visits, predominantly for physical trauma. Accordingly, primary healthcare capacity for the management of physical trauma and CVD should be strengthened at the grassroots level to enhance the resilience of emergency medical systems.