In most cases, the annual East Asian Monsoon brings heavy rains and widespread flooding to southeast China and drought conditions to the northeast. At various points throughout history, however, large volcanic eruptions have upset the regular behavior of the monsoon.
Sulfate aerosols injected high into the atmosphere by powerful eruptions can reduce the land-sea temperature contrast that powers the monsoon circulation. How this altered aerosol forcing affects precipitation is not entirely clear, however, as climate models do not always agree with observations of the nature and scale of the effect.
Using two independent records of historical volcanic activity along with two different measures of rainfall—including one 3,000-year-long record derived from local flood and drought observations—Zhuo et al. analyzed how large volcanic eruptions changed the conditions on the ground between 1368 and 1911. Understanding the effect of sulfate aerosols on monsoon behavior is particularly important now as researchers explore aerosol seeding as a means of climate engineering.
The authors found that large Northern Hemispheric volcanic eruptions cause strong droughts in much of eastern China. The drought begins in the north in the second or third summer following an eruption and slowly moves southward over the next 2 to 3 years. They found that the severity of the drought scales with the amount of aerosol injected into the atmosphere and that it takes 4 to 5 years for precipitation to recover. The drying pattern agrees with observations from three large modern eruptions.
China’s northeast is the country’s major grain-producing region. The results suggest that any geoengineering schemes meant to mimic the effect of a large volcanic eruption could potentially trigger devastating consequences for China’s food supply. (Journal of Geophysical Research: Atmospheres, doi:10.1002/2013JD021061, 2014)
—Colin Schultz, Writer