Global patterns of river flow change significantly in the year or two following a volcanic eruption, shows a study published online in Nature Geoscience. The findings suggest that future eruptions could affect water availability in many regions throughout the world.

In regions that are usually wet, reductions in rain and snowfall have previously been documented in the years following volcanic eruptions. However, whether any of these changes in precipitation systematically translate into variability in river flow was unclear.

Carley Iles and Gabriele Hegerl studied observational records of streamflow volume for 50 major world rivers, with each record including at least two and up to six large volcanic eruptions in the twentieth and late nineteenth century. In the years following these eruptions, they find statistically significant reductions in streamflow in some rivers, such as the Amazon, Congo and Nile, and in larger regions such as high-latitude Asia. In contrast, they found that streamflow consistently increased in the southwestern US and the southern part of South America after a large eruption took place. The authors also note that some geoengineering schemes may have a similar effect.