Global response of floods to tropical explosive volcanic eruptions

Tropical volcanic eruptions with a high volcanic explosivity index (≥5) impact the global climate system, but little is known about how they affect floods. Here, leveraging global climate model simulations with volcanic forcings and statistical relationships between seasonal climate drivers and peak discharge, we investigate the response of seasonal peak discharges at 7,886 streamgauges worldwide to three tropical explosive volcanic eruptions in the twentieth century: Agung 1963 (Indonesia), Santa Maria 1902 (Guatemala) and Pinatubo 1991 (Philippines), whose stratospheric aerosol plumes were distributed primarily in the Southern Hemisphere, primarily in the Northern Hemisphere and symmetrically across both hemispheres, respectively. For the eruptions with interhemispherically asymmetric aerosol distributions, tropical regions show more immediate and widespread responses to the eruptions than non-tropical regions, with a distinct interhemispheric contrast of decreasing (increasing) peak discharges in the hemisphere in which the eruption happened (did not happen). For the case of symmetric aerosol distribution, tropical (arid) regions have the strongest tendency to respond to the eruption by decreasing (increasing) peak discharges in both hemispheres. These regional flood responses are attributed mainly to seasonal precipitation changes across the climate regions. Beyond direct volcanic hazards, our study provides a global view of the secondary flood hazards resulting from hydroclimatic changes induced by large explosive eruptions.