Tropical Cyclone Stalling Shifts Northward and Brings Increasing Flood Risks to East Asian Coast

Tropical cyclone (TC) stalling has been widely perceived to yield a greater threat of flooding. Understanding the effect of stalling and its long-term trends will enhance adaptation strategies to cyclone-associated disasters. We show that stalling prolongs western North Pacific TCs to live 24 hr longer and produces 23% greater 24-hr rainfall accumulations in a more concentrated area, which is more prominent over a 72-hr rolling period. More importantly, we discover a northward migration of TC stalling (similar to 0.7 degrees N decade(-1)) over 1979-2020, bringing increasingly higher flood risks to the highly-populated East Asian coast. Further diagnoses suggest the role of binary cyclone interactions in TC stalling, whereby the second larger TC slows down the smaller one by weakening the northwestward steering flows. The northward shift of TC stalling can be explained by a similar trend in binary TC cases and environmental fields. Our findings are robust across various best track and precipitation products. Plain Language Summary Tropical cyclone (TC) stalling occurs when the cyclone resides in a small area for long. It is widely perceived to produce increased accumulated rainfall and flood risks in coastal areas nearby. However, little effort has been made to comprehensively quantify the difference in the general properties and hydrological impacts between stalled and non-stalled TCs, as well as the spatial pattern and the possible causes of TC stalling. This study addresses the above research gaps by focusing on TC stalling over the western North Pacific (WNP) since the satellite era (1979-2020). We discover that stalling enables TCs to live significantly longer and produce greater rainfall accumulations in a more concentrated area, which is more prominent when measuring over a long rolling period (e.g., 72 hr). We highlight a northward migration of TC stalling phenomenon over the past decades, bringing increasingly greater flood risks to the highly-populated East Asian coast, especially the Pearl River Delta. The plausible physical causes of stalling are discussed and our conclusions are validated across various sources of data. Findings here improve the understanding of TC stalling and stress the need for future adaptations against more frequent stalling events along the East Asian coasts.