Characteristics and synoptic conceptual model of rainstorms in Wenshan based on dense surface precipitation observations

To improve the forecasting and early warning capability for rainstorms in Wenshan, Yunnan, and enhance understanding of rainstorm occurrence over complex terrain, this study analyzed the fine-scale spatiotemporal distribution characteristics of rainstorms, classified 110 rainstorm events by weather system type, conducted composite analyses, and developed different synoptic conceptual models for different rainstorm types. The analysis was based on hourly precipitation data from 149 automatic weather stations in Wenshan and NCEP FNL reanalysis data during 2014-2023. The results show that: (1) Rainstorms in Wenshan exhibit a slightly decreasing trend in frequency, but increasing intensity with shorter durations and increasing extremes. The diurnal variation of short-duration heavy rainfall shows a bimodal pattern, with a primary peak at 23:00 and a secondary peak at 18:00 Beijing time (BT). Events with intensities of 20-39.9 mm·h⁻¹ and 40-79.9 mm·h⁻¹ occur most frequently during the night and early evening, respectively, while events ≥80 mm·h⁻¹ mainly occur in the early morning. (2) The distribution of rainstorm days generally presents a pattern of "more in the north and south, less in the middle." High-incidence areas are mainly located on windward slopes and in trumpet-shaped topography, and localized maximum in daily precipitation occur primarily in the southern and northern parts of Wenshan. (3) Rainstorm events in Wenshan can be classified into six types, among which the shear-line type (51.8%), the two-high convergence type (20.0%), the westward-moving typhoon type (14.5%), and the southern-branch trough type (10.9%) are predominant. The shear-line type exhibits the strongest precipitation intensity. The two-high convergence type and the westward-moving typhoon type are more significantly affected by topography, while the southern-branch trough type shows the most pronounced localization. (4) The synoptic conceptual models reveal the key influencing systems and the criteria for precipitation areas for each rainstorm type: the shear-line type is jointly influenced by the shear lines at 850 and 700 hPa; the two-high convergence type is associated with the vortex or the convergence shear line within the convergence zone; the westward-moving typhoon type develops within southeasterly typhoon airflow; and the southern-branch trough type is situated in the lower-level convergence shear zone ahead of the trough. (5) The westward-moving typhoon type has the most abundant water vapor and the strongest water vapor convergence, but its thermal instability is relatively weak. The two-high convergence type and the shear-line type have comparable water vapor and thermal conditions. The southern-branch trough type has the weakest water vapor and thermal conditions but the strongest ascending motion. All four types exhibit a dynamic configuration characterized by upper-level divergence and lower-level convergence. These results can provide a clear reference model for local rainstorm forecasting.