The "7.20" Zhengzhou torrential rainfall is the most severe storm in the 21st century, characterized by long persistence and intense hourly precipitation. Through comparative analysis of PBL (Planetary Boundary Layer) eddy transport for this instantaneous precipitation process, this study attempts to investigate PBL structure and turbulent diffusion impacts on heavy precipitation intensity. Three comparative experiments are conducted by tuning coefficients of local eddy diffusion and counter-gradient term. Results show that PBL turbulent transport has strong influences on severe hourly precipitation during the "7.20" Zhengzhou torrential rainfall event. It is found through comparison that the decrease in local eddy diffusion noticeably leads to weakening in precipitation intensity and the counter-gradient term mainly results in changes in rainfall location and evolution. Furthermore, PBL eddy transport can modulate large-scale atmospheric conditions for heavy storms, such as local water vapor supply and atmospheric instability. Finally, the eddy vapor and heat transports can notably modify the distribution, intensity and evolution of moisture flux convergence and PBL atmospheric instability, and thus exhibit great influences on this severe storm simulation.

Accurate forecasting of heavy precipitation in central China is still a challenge, within which a key issue is our still incomplete understanding of the convective systems (CSs) responsible for such events. In this study, through use of an iterative rain-cell tracking algorithm, the macroscale characteristics (scale, intensity, duration, etc.) of the CSs that produced 595 short-term heavy precipitation events in Hunan Province, central China, are quantitatively analyzed, based on radar reflectivity, echo top, and rainfall observations at 1-km and 6-min intervals in April–September of 2016–2018. The results show that CSs present significant seasonal and diurnal features. Spring CSs usually cover a larger echo area with stronger convective cores and thus generate more precipitation than summer CSs, though summer CSs develop more vigorously and frequently. CSs initiated at 1400–1600 local time are characterized by the strongest convection and a smaller spatiotemporal scale, causing violent and transient showers with typical areal precipitation of 0.5–1 mm km⁻², but less total precipitation. Further analyses of the relationships among the scale, intensity, duration, and total precipitation of CSs reveal that the convective intensity is linearly correlated to the spatiotemporal scale of CSs, with the duration increasing on average by 0.0372 h dBZ⁻¹; the echo area is significantly correlated to the total precipitation, and the duration and rainfall amount are connected with the area expansion rate (AER) of CSs: when the AER exceeds 50%, CSs expand rapidly with increasing total precipitation, but the duration is shorter. These findings provide a helpful reference for the forecasting of short-term heavy precipitation induced by CSs in central China.