Construction and Variation of the Regional Rainstorm Grade Series for the Hekouzen-Shanmenxia Basin of the Yellow River in the past 200 years

According to the temporal and spatial distributive concentration and the recurrence of the regional rainstorms over the Hekouzen-Shanmenxia basin,and their closing relationships with the magnitude order of flood peaks and the number of occurrences of flood at Sanmenxia (Shanxian),the regional grade index series from 1770-1989 is constructed by using the gage pile date at Wanjintan in Shanxian county,the historical information regarding stormflood disasters,and the recorded pr ecipitation data for the Hekouzen and Shanmenxia basin.From the analysis of the grade series it follows that the regional rainstorms,just like other meteorological elements,have their own variation pattterns,and that six prominent cycles of the regional rainstroms are detected for the past 200 years period.