Abstract:Based on the hourly precipitation data in the wet season during 2011-2020 from the gradient observation system between Cangshan Mountain and Erhai Lake of Dali National Climate Observatory, the diurnal variation characteristics of precipitation at the mountain top, hillside and dam area are analyzed. The results show that the diurnal variation of rainfall amount at the dam station presented one peak, while that at mountain side and hilltop stations presented two peaks. The diurnal variation of rainfall frequency at dam and hilltop stations displayed a single peak, while that at the hillside station was relatively stable. All hourly rainfall amount and rainfall frequency for a whole day basically increased with the rise of altitudes. The diurnal variation of rainfall intensity at hilltop station exhibited double peaks, while that the hillside and dam stations showed remarkable fluctuation with small values in the afternoon and large values over night. There were no significant differences in rainfall intensity from 14:00 BT to 17:00 BT among the three stations, but the rainfall intensities at the hillside and dam stations were obviously greater than that at the hilltop station during other periods. The rainfall amount with a duration of 2-16 h over night was a large value area, which maintained a longer duration with the rise of altitude. The rainfall amount with a duration of less than 6 h during the daytime was a large value area, and the occurrence of the large value was delayed with the increase of altitude. The rainfall frequencies at all the three stations had a large value area during the day (night) when the rainfall duration was less than 6 h, while that at the hilltop station only had a large value area at night when the duration was 7-18 h. The rainfall frequencies over night were greater than that during the day at the dam and hilltop stations, while there was little difference in the rainfall frequency during the day and night at the hillside station. The accumulated rainfall amount and frequency of long (medium and short) duration increased (decreased) with the increase of altitudes. The contribution of long duration rainfall amount (long duration rainfall frequency) to accumulated rainfall amount (accumulated rainfall frequency) at each station was the largest, but the contribution of short duration rainfall amount (medium duration rainfall frequency) was the least.