Development and Distribution Characteristics of Debris Flow in Zhejiang Province and Its Regional Forecast

Debris flow is one of the major geohazards that may lead to mass injuries or casualties in Southeast China, however, studies on the development law and predictions need to be furthered. This study presents the characteristics of debris flow development and spatial-temporal distribution in Zhejiang Province based on the results of small drainage geohazards survey. It is found that the debris flows mainly occur in Meiyu period (i.e. 27.4%) and typhoon season (i.e. 70.1%). Generally, the debris flows in typhoon season are mostly distributed in southeast Zhejiang, whereas those in Meiyu period are distributed in west. Based on that, rainfall thresholds of different raining seasons have been determined. Separate forecasting models based on extension method have been established taking small drainage as assessment unit, where the susceptibility map, 24-hour forecast rainfall and effective antecedent precipitation are employed as model inputs. Two debris flows, occurred in Yunna typhoon period in 2004 and in Meiyu period in June, 2006, were selected to validate the established forecasting models. The results in terms of hazard intensity (R) and receiver operating characteristiccurve (ROC) confirm the feasibility of the proposed scheme for debris flow forecasting.