Seasonally Modulated Tropical Drought Induced by Volcanic Aerosol

Abstract

Major volcanic events with a high loading of stratospheric aerosol have long been known to cause cooling, but their impact on precipitation has only recently been emphasized, especially as an analog for potential geoengineering of climate. Here, the authors use a coupled atmosphere-ocean-land-vegetation model in conjunction with observations to study the effects of volcanic aerosol on the tropical and subtropical precipitation. The small internal variability in the model enables a clear identification of the volcanic impact, which is broadly supported by observations, especially for the large Pinatubo event. Area averaged rainfall over land between 408S and 408N decreases by about 0.15 mm day 21 , 4-5 months after the height of a major volcanic aerosol loading, such as from Pinatubo, with regional changes as large as 0.6 mm day 21 or higher, such as over the Amazon and equatorial Africa. These anomalies migrate seasonally, following the movement of monsoon rainfall. This is because the low heat capacity of the land leads to rapid response of rainfall there, owing to the energy imbalance caused by volcanic aerosol cooling. In contrast, precipitation response over the ocean is much slower and considerably damped because of the much larger heat capacity. In addition, the difference in heat capacities over land and over ocean leads to an anomalous land-sea thermal contrast, which could further contribute to the reduction of rainfall over land. The volcano-induced drought may have significant impact on the ecosystem, agriculture, and the carbon cycle, especially in the monsoon regions.

Assessing the impact of large volcanic eruptions of the last millennium (850–1850 CE) on Australian rainfall regimes

“…8, 9 and 11) is in agreement with several papers that identified a precipitation surplus over Australia following large volcanic eruptions (Schneider et al, 2009;Joseph and Zeng, 2011). Our results suggest that the direct effect of volcanic aerosols on precipitation overrode the impact of the IOD and ENSO on Australian precipitation in the years following large tropical volcanic eruptions.…”

“…The direct radiative effect of volcanic aerosols has been found to cause global precipitation deficits for up to 5 years post-eruption (Robock and Lui, 1994;Iles et al, 2013Iles et al, , 2015Gillett et al, 2004;Gu and Adler, 2011;Soden et al, 2002;Joseph and Zeng, 2011;Schneider et al, 2009;Timmreck et al, 2012). However, these deficits have been shown to vary seasonally (Joseph and Zeng, 2011), and cause positive precipitation anomalies over the north-west (NW) and southeast (SE) of Australia in the Southern Hemisphere (SH) winter and early spring (July to September), despite significant precipitation deficits in the summer (Joseph and Zeng, 2011;Schneider et al, 2009).…”

“…However, these deficits have been shown to vary seasonally (Joseph and Zeng, 2011), and cause positive precipitation anomalies over the north-west (NW) and southeast (SE) of Australia in the Southern Hemisphere (SH) winter and early spring (July to September), despite significant precipitation deficits in the summer (Joseph and Zeng, 2011;Schneider et al, 2009). This study explores these relationships between volcanic eruptions and Australian rainfall during JASON (July-November), with reference to the direct radiative effect and the feedback effects of the ENSO and IOD.…”

Assessing the Impact of a Future Volcanic Eruption on Decadal Predictions

“…2). This is in agreement with previous studies (Iles et al, 2013;Joseph and Zeng, 2011). In the global precipitation-maps, we see a reduction of precipitation for both experiments through the volcanic aerosol in most regions in the first four prediction years (Fig.…”

The Role of Volcanic Activity in Climate and Global Change

“…Joseph and Zeng [87] employed a coupled atmosphere-ocean-land-vegetation model of intermediate complexity to study the volcanic aerosol effect on tropical precipitation. They found that the precipitation response over the ocean is slower and weaker than over the land due to the ocean's larger thermal capacity.…”