On disaster threshold of landslide and debris flow rainfall in Wenchuan County

Data of GPM L3 precipitation from 2001-2020, catalogue of hidden danger points of landslide and debris flow disasters in flood season in Wenchuan County in 2018 from the second Qinghai-Tibet scientific expedition, were used to select 11 extreme precipitation indexes taking into account of intensity, relativity, absoluteness and sustainability, to reveal the spatiotemporal evolution law of extreme precipitation in Wenchuan County．Cumulative rainfall-duration relationship threshold (E-D) model was constructed, rain field segmentation method was optimized, rainfall threshold of rainfall-type landslides and debris flows in Wenchuan County was quantified, risk grade of hidden danger points of rainfall-type landslides and debris flows were evaluated for period 2001-2020．The change of extreme precipitation index in most villages and towns in Wenchuan County was found not obvious, most indexes showed spatial distribution of low in the north, high in the south, low in the west and high in the east．The relativity index, intensity index and partial persistence index of extreme precipitation were very similar in spatial distribution．The precipitation in the eastern and southern areas of Wenchuan County showed high intensity, relativity and persistence, likelihood for geological disasters due to extreme precipitation was high．The E-D threshold curves of rainfall-type landslides and debris flows in Wenchuan County were: E = 41.69·D^0.84(3≤D≤6) and E = 81.28·D^0.36(3≤D≤23), respectively．The “easy-to-happen” hidden danger points of rainfall-type landslides in Wenchuan County accounted for 46.2%, being concentrated in the north of Shuimo Town, the east of Xuankou Town, the southeast of Caopo Township, the south-central of Mianqi Town, the southeast of Gengda Town, the east of Yingxiu Town and the northeast of Wolong Town．The “easy-to-happen” hidden danger points of rainfall-type landslides accounted for 13.84%, being concentrated in the southeast of Caopo Township and the west of Yinxing Township．The distribution of “easy to occur” and “relatively easy to occur” hidden danger points of landslides and debris flows was highly consistent with the intensity, relativity and partial sustainability indexes of extreme precipitation．The present work provides detailed forecast and early warning for disaster prevention and mitigation of landslides and debris flows caused by extreme rainfall events in Wenchuan County．