Analysis on typical and atypical spatiotemporal characteristics of Meiyu precipitation over Zhejiang Province in 2024

The spatial distribution of Meiyu precipitation in Zhejiang Province is highly heterogeneous, with pronounced interannual variability. Investigating both its typical and atypical characteristics is therefore essential for understanding precipitation anomalies. Using daily precipitation observations from 66 national meteorological stations in Zhejiang Province from 1973 to 2024 (June-August), daily NCEP/NCAR reanalysis data, the East Asian summer monsoon, western North Pacific subtropical high (hereafter referred to as the subtropical high), and South Asian high indices from the Climate Monitoring and Prediction Analysis System (CIPAS3.1), as well as monthly ERSSTv5 sea surface temperature (SST) data, this study first analyzes the spatial and temporal characteristics of the 2024 Meiyu precipitation, then investigates its stage-dependent characteristics, associated atmospheric circulation, and preceding SST background, and finally preliminarily explores the diversity and complexity of normal Meiyu years. The results are as follows. (1) The statistical characteristics of the 2024 Meiyu over Zhejiang Province were generally close to the climatological mean. The Meiyu season started on 9 June and ended on 4 July, and both the Meiyu precipitation amount and Meiyu intensity index were within the normal range, indicating a typical normal Meiyu year. However, its precipitation exhibited atypical spatial distribution characteristics, with an overall pattern of “more precipitation in the west and less precipitation in the east”. Precipitation intensity was relatively strong, the number of days with moderate or heavier precipitation increased significantly, and some non-Meiyu regions also experienced notable precipitation anomalies, with the non-Meiyu precipitation amount reaching nearly 90% of the Meiyu precipitation amount. (2) The 2024 Meiyu precipitation process showed distinct stage-dependent characteristics. During 9-18 June, heavy precipitation mainly occurred in southwestern Zhejiang, while after 19 June, the precipitation center shifted to northwestern Zhejiang. Around 19 June, a critical transition occurred due to the coordinated influences of an enhanced East Asian summer monsoon, the development and northward shift of the subtropical high, and the adjustment of the South Asian high, leading to intensified precipitation and a northward migration of the precipitation center. The preceding winter-spring El Niño event and multi-basin SST anomalies affected the early-summer circulation by enhancing moisture transport and suppressing southward cold-air intrusions. Their opposite effects may have partially offset each other, contributing to the near-normal Meiyu intensity in Zhejiang Province in 2024. (3) The precipitation spatial patterns of the nine normal Meiyu years in Zhejiang Province did not always exhibit the typical “central and northern Zhejiang Meiyu” pattern. Large interannual differences existed in precipitation distributions, and heavy precipitation could also occur in non-Meiyu regions. These findings indicate that a normal Meiyu precipitation amount does not necessarily correspond to a precipitation spatial pattern close to the climatological mean state.