Evaluation and analysis of extreme continuous precipitation induced disasters of Yan' an city in 2013 July

By using the precipitation data and geographic disasters data, in this study we analyzed the characteristics of extreme and disastrous precipitation in Yan' an City during July 2013 from several angles including maximum precipitation during 1 h, 3 h, 6 h, 12 h and daily maximum precipitation, 3-day continuous maximum precipitation and monthly precipitation and so on. In the study we also analyzed the relationship between process accumulated precipitation (R_L) and process accumulated geological disaster frequency (D_L), daily precipitation (R_R) and daily geological disaster frequency (D_R). The results show that: (1) The monthly mean precipitation in Yan'an city during July 2013 is 419 mm, which is a thousand year frequency extreme precipitation. (2) R_L is closely related to D_L, and the relationship between the two can be described by piecewise function. (3) There are no group geological disasters in Yan' an city when R_L < 137 mm, seldom when 200 mm > R_L≥137 mm and R_R < 50 mm, and frequent when R_L≥200 mm or 200 mm > R_L≥137 mm and R_R≥50 mm. (4) The precipitation of Baota district in July 2013 is 568 mm, exceeding a 1 000-year frequency. There are no group geological disasters when R_L < 332 mm, and frequent group geological disasters when R_L≥332 mm.