Evolution of Precipitation in Zhengzhou over the Past 42 Years and the Multi-scale Mechanisms of the "720" Extreme

Based on NASA MERRA-2 and Zhengzhou Meteorological Bureau precipitation data from 1982 to 2024, this study analyzes the evolution of annual precipitation in Zhengzhou and the mechanisms associated with the "7·20" extreme rainstorm. Results show an upward trend in grid-cell average annual precipitation at a climatic tendency rate of 6.2 mm·a⁻¹, with substantial interannual fluctuations. The interannual variation in annual precipitation is closely associated with the frequency of heavy precipitation days (≥20 mm·d⁻¹). The 2021 precipitation maximum was largely associated with a single extreme weather process that contributed 41.6% of the annual precipitation total, rather than with an increase in the number of heavy precipitation days. Mechanistic analysis indicates that the "7·20" rainstorm was associated with the anomalously northward-positioned western Pacific subtropical high, remote moisture transport by Typhoons In-Fa and Cempaka, and topographic forcing. The 2021 event highlights the potential for low-frequency, high-intensity precipitation extremes in Zhengzhou and the need for urban hydrological planning to consider scenario-based stress testing for such events.