Mount Pinatubo eruption caused the major East China flood in 1991

by C. Xing & F. Liu, Jan 2023 in InnovativeGeoscience

The devastating flood of 2020 along the Yangtze River serves as a painful reminder of the 1991 East China’s largest flood. The latter event profoundly impacted the Yangtze-Huaihe River basins (YHRBs), causing extensive damage to both human lives and property1. The flood engulfed numerous villages and cities across seven provinces in East China, affecting over 15,000,000 hectares of farmland and approximately 100 million people. In response, millions of individuals in Anhui and Jiangsu provinces were forced to evacuate, with some seeking refuge on the banks of the Huaihe River. Gaining a comprehensive understanding of the contributing factors to this historically significant flood will enhance our ability to predict the East Asian summer monsoon and mitigate related climate disasters. Over the past three decades, this pursuit has been a persistent challenge1,2,3.

The 1991 East China flood was attributed to prominent intraseasonal oscillations, as evidenced by three episodes of heavy rain occurring from mid-May to mid-July over the YHRBs2, primarily linked to the persistent Meiyu front during early July1. The stable western Pacific subtropical high (WPSH), which plays a crucial role in influencing the East Asian monsoon by altering the convergence of southeasterly and southwesterly, provided substantial support for the prolonged existence of the Meiyu front in 19911; However, the reason behind the prolonged stability of the WPSH during that specific period remains a mystery.

No internal climate variability modes were reported to be in their most flood-favorable conditions during 1991, and the effect of external forcing on this flood disaster was not taken into consideration at all. Half a month before the flood, the Mount Pinatubo (located at 120.4ºE, 15.1ºN) in Luzon, the Philippines, explosively erupted on June 15th, 1991, which later is known as one of the strongest volcanic eruption in the past century. This eruption released approximately 20 Tg of SO2 into the tropical stratosphere4, which can form stratospheric aerosol that impact the global radiative balance. The stratospheric volcanic aerosol acts as a major forcing on the climate by cooling the global surface and slowing down the water cycle on annual to decadal timescales5. However, it remains unclear whether explosive volcanic eruptions have short-term impacts on the climate, particularly on the intraseasonal timescale.