Analysis on duration and temporal and spatical distribution characteristics of hourly extreme rainfall in summer in Inner Mongolia

Using hourly precipitation data at 117 national stations in summer from June to August during 1991-2013 in Inner Mongolia, the threshold value of hourly extreme rainfall process (HERP) was defined by the Gumbel threshold method. Duration and temporal and spatical distribution characteristics of HERP was studied in summer in Inner Mongolia. The results show that:(1) the threshold value of HERP increases from western regions (5-10 mm·h^-1) to eastern regions (40-55 mm·h^-1), while relative intensity of HERP decreases from western regions to eastern regions. There is a longer duration than 7 h in the southwest region, in the south region of Yinshan mountain and in the east region of Greater Khingan Range mountain rage in Inner Mongolia, while HERP lasts for a relatively short time (within 6 h) in the remaining region. (2) HERP of 1-3 h duration has the highest frequency. The shorter duration of HERP, the stronger the precipitation intensity is before the peak value of HERP occurs. HERP of 4-6 h duration has the maximum deviation, and the second are 1-3 h and 7-12 h duration of HERP. (3) HERP occurs mainly in the late July and the peak value of HERP delays from 17:00 to 20:00 in recently 23 years. HERP is relatively low from 1990 to 2010, which likely caused that the HERP of 4-6 h and 7-12 h durations are less frequently observed. HERP increases obviously during 2011-2013, which probably causes that the HERP of 1-3 h, 4-6 h and 7-12 h durations increase at the same time.