Hydroclimatic whiplash events and social inequalities shape dengue outbreaks at the global scale

Dengue is expanding worldwide under the combined pressures of climate change, rapid urbanization, and persistent social inequalities. While temperature and rainfall are established drivers of transmission, less is known about whether rapid transitions between dry and wet extremes (i.e., hydroclimatic whiplash events) influence dengue outbreak onsets and how social inequalities modify these associations. In this study, we examine dry and wet extremes and dry-to-wet (D2W) and wet-to-dry (W2D) whiplash events at subnational scale across Latin America, Southeast Asia, the Philippines, and Australia. Event coincidence analysis showed that dengue outbreak onsets frequently followed whiplash events, particularly W2D transitions at short lags. Whiplash characteristics were associated with outbreak onset, but duration and severity alone did not explain emergence. Temperature, humidity, inequality, and urban context modify dengue risk during hydroclimatic extremes. These findings suggest that whiplash events influence dengue risk and may support surveillance when interpreted alongside social vulnerability and local epidemiological information.