The severe drought-flood abrupt alternation event over the Huanghe-Huaihe Basin in summer 2024: Sequential impacts of Barents Sea ice and North Atlantic sea surface temperature

Based on the monthly ERA5 and other reanalysis data from 1980 to 2024, this study investigates the physical mechanisms by which Barents Sea ice and the North Atlantic Tripolar (NAT) jointly drive drought-flood abrupt alternations (DFAAs) over the Huanghe-Huaihe Basin (HHB) during June and July, and discusses how they contribute to the record-breaking DFAA in summer 2024. The key results are as follows: Excessive Barents Sea ice in April can persist until June, triggering upper-level Rossby wave trains via sea ice-atmosphere coupling, which leads to the anomalous anticyclone over northern China alongside a barotropic cyclone over the East China Sea. This process blocks the transportation of cold air and moisture, inducing drought in the HHB. Concurrently, the spring NAT anomalies can persist into July, stimulating upper-level Rossby wave trains that generate the anticyclone over central China, promoting upward atmospheric motion. Additionally, positive tropical sea surface temperature anomalies (SSTAs) associated with the NAT trigger equatorial Rossby wave trains, leading to the Pacific-Japan pattern (PJ) conducive to enhanced precipitation over the HHB. The drought induced by above-average sea ice is predominantly confined to June, whereas the NAT-driven rainfall primarily occurs in July. The sequential influence finally results in DFAAs over the HHB. Notably, in 2024, Barents Sea ice and the NAT attained their second-highest recorded levels since the onset of the 21st century and 1980, respectively, thereby contributing to the unprecedented DFAA in the HHB.