Analysis of precipitation characteristic differences and their causes between dry and wet basins on the southern section of the Hengduan Mountains

The southern section of the Hengduan Mountains is characterized by complex terrain and frequent meteorological disasters, with distinct local heterogeneity in precipitation distribution being frequently observed. To reveal the characteristics and causes of precipitation distribution in this region, this study utilized hourly precipitation data from 213 regional automatic weather stations and 12 national meteorological stations during 2019−2023, as well as two national stations (Binchuan and Dali) during 2004−2023. The differences in precipitation characteristics between typical dry and wet basins, represented by the Binchuan and Dali stations, were analyzed. The causes of these differences were further examined using Dali Doppler weather radar data during 2019−2023. The results are as follows. (1) The annual precipitation amount and frequency in the southern Hengduan Mountains generally displayed a trend of lower values in the east and higher values in the west, but the difference in precipitation intensity was relatively small. The annual, monthly, and daily precipitation amount and frequency of the wet basin were all higher than those of the dry basin. The precipitation in the wet basin peaked in August, while that in the dry basin reached its peak in July. (2) The diurnal variation of precipitation in the wet basin showed a single-peak pattern, with the peak occurring at 05:00 (Beijing time, referred to as BT below). In the dry basin, it presented a bimodal pattern, with peaks occurring at 05:00 BT and 15:00 BT. The frequency and intensity of precipitation in the wet basin were significantly higher during nighttime than during the daytime, while an opposite diurnal distribution was observed in the dry basin. (3) Short-duration precipitation events dominated both the dry and wet basins. However, the average precipitation duration in the wet basin was 2 h longer than that in the dry basin, making it the primary contributor to regional precipitation. During regional coincident precipitation events, the wet basin was characterized by high-frequency, medium- to long-duration precipitation, whereas in the dry basin, precipitation was mainly contributed by short-duration convective precipitation occurring in the afternoon. (4) The diurnal variation of radar reflectivity factor during coincident precipitation events indicated that precipitation systems generally propagated from west to east. During the propagation, the intensity tended to weaken, making it difficult to reach the dry basin. This resulted in the higher frequency and duration of precipitation in the wet basin compared to the dry basin. These findings provide a reference for refined weather forecasting and regional water resources management in the southern section of the Hengduan Mountains.