Relationship between Precipitation and Terrain over the Qilian Mountains and Their Ambient Areas

Daily precipitation observations of 08:00～20:00 in daytime,20:00～08:00 in nighttime and 20:00～20:00 in the whole day from 55 meteorological stations during 1960-2004 over the Qilian Mountains and their ambient areas(90°～104° E,32°～42° N)are primarily analyzed to study the temporal and spatial distributions of precipitation in different categories of intensity,the frequency and intensity of precipitation and their relations to elevation.The elevations of maximum total rainfall for different precipitation's intensities and seasons are found out.The frequency of flurry days linearly increases well with elevation over the Qilian Mountains.However,the days of middle rain and others have something to do with slopes and geographic locations.The maximum days of rainfall are 143 d at the elevation of 4 850 m.The first peak of total rain days and the total rainfall is at the elevation of 3 700 m or so,and the second peak of that is at the elevation of 2 700 m or so.Furthermore,it is diagnosed from the data of drought and wet years that the elevation of maximum rainfall is possibly dependent on the two maximum relative humidity centers and the elevation of the corresponding stronger cold air activity center,except for the effect of ground altitude.