Influences of Volcanic Eruptions on Ongoing Multi-year Droughts over Europe

Large volcanic eruptions alter the Earth's radiative balance inducing a decrease in the global surface temperature and changes in regional precipitation. Although the post-eruption influences on hydroclimate over Europe have been examined in many studies, how large eruptions affect ongoing extreme hydroclimate conditions, such as droughts, are still not fully addressed. Here, we investigate the effects of volcanic eruptions on multi-year droughts over Europe during the last 2000 years. For this end, we use two records of volcanic eruptions, Evolv2k and IVI2, tree-ring-based reconstructed drought indices, and climate model simulations from the Community Earth System Model (CESM).

The tree-ring-based reconstruction indicates that large volcanic eruptions can alleviate ongoing droughts in southern Europe by wettening the region and decreasing the intensity of droughts during the first two years after the eruptions. Over central Europe, droughts are not strongly affected by the eruptions. Simulations from CESM show a similar post-eruption hydroclimate response that agrees with the proxy record. However, the model indicates that the influences of eruptions on droughts are dependent on the season of occurrence of eruptions. Over southern Europe, eruptions occurring in January exhibit more tendency to reduce the duration of ongoing droughts, while those occurring in April do not present a significant association with droughts. This result can be related to the timing of the maximum peak of sulfate injections into the stratosphere. Eruptions occurring in January reach their maximum peak of sulfate injection in summer causing a decrease in surface temperature which in turn reduces the land-atmosphere interaction that has sustained multi-year droughts over the region. This effect is not apparent when the eruptions occur in spring with their maximum sulfate injection reaching in autumn and winter. However, the influence of the season of occurrence of eruptions is not strong in central Europe.

Our result highlights the importance of correctly assessing the timing of past eruptions and provides some insights into the effects of eruptions over drought-prone regions, such as southern Europe, where droughts are expected to intensify in the future warmer world.