Rainstorm indices and spatio-temporal change of torrential rain events in Tibet

Based on the daily precipitation datasets recorded by 38 meteorology stations in Tibet from 1971 to 2012, the cumulative distribution function value, percentile value and standard deviation were used to define rainstorm indices, and the spatiotemporal change of torrentialrain events in Tibet was analyzed. The results indicate the following. (1) The thresholds of rainstorm varied in a range of 17.2-41.2 mm, with a maximum in Nyalam and a minimum in Shiquanhe. Its spatial distribution decreased from southeast to northeast. (2) The annual rainstorm days were 0.3-2.9 d, and its spatial distribution decreased from east to west, which was consistent with annual rain days and annual precipitation.(3) There was a significant 4-5 year period of frequency of rainstorm days before 1995 and 2-4 year after 1995 in the eastern area. In southern area, the significant frequency was 2-4 year and 8-10 year from 1980s to 2010s while it was 3-6 year in the river area all the time.(4) The abrupt change of rainstorm days began at 1982 in southern region, and 1976 in river region while there was no obvious change in eastern region. Furthermore, the rainstorm days significantly increased over 1988-2012 in southern region, and 1998-2004 in river region.