Regression analyses for the minimum intensity-duration conditions of continuous rainfall for mudflows triggering in Yan'an, northern Shaanxi (China)

An empirical minimum intensity-duration (I-D) condition of continuous rainfall for mudflows triggering is proposed for Yan'an, northern Shaanxi, China, where rainfall-induced mudflows occur frequently. Adopting the quantile-regression method, a program was built using R programming language and statistical computing environment, and 175 continuous rainfall records were analyzed objectively. The 35th percentile regression line was determined as the minimum I-D condition of continuous rainfall that can potentially trigger mudflows within the duration interval of 24-336 h, where I is measured in millimeters per hour and D in hours. Comparison of the minimum I-D condition of continuous rainfall determined by this study with those rainfall I-D thresholds developed for the world and other regions reveals that lower rainfall intensity has the potential to trigger mudflows in the Yan'an district, which proves the necessity of defining regional minimum rainfall I-D conditions and site-specific operational rainfall I-D thresholds for mudflows triggering in Yan'an.