The Fuyang shallow landslides triggered by an extreme rainstorm on 22 July 2023 in Zhejiang, China

Abstract

An extreme rainstorm hit Fuyang District, Zhejiang Province, China, on 22 July 2023. A record-breaking 320 mm of rain fell in less than 48 h. In the early evening of 22 July, more than 145 shallow landslides emerged in a 20 km² hilly area of Fuyang amid turbulent flash flooding and claimed five lives. Post-event field investigations and laboratory experiments were urgently carried out, targeting two geologically typical shallow landslides, to decipher the initiation mechanism and distributing features of the regionally distributed landslides. The main findings are summarized as follows: (1) The week-long rainfall preceding the event and the intense storm on 22 July are presumably primary triggers for the landslides. Besides rainfall, convergent topography of hollows may be another important factor influencing the initiation of landslides. (2) The dominant moso bamboo has an extensive and interconnected root system, which could significantly stabilize slopes by enhancing soil strength and restricting cracks. (3) The sedimentary Heshangzhen Group area is more susceptible to landslides than the igneous Shuangxiwu Group area. Bedrock lithologies affect landslide distribution through controlling soil structures and properties to shape the hillslope hydrology and also through influencing landscape morphology. This study offers new evidence and insights into the lithological control on landslide initiation and distribution.