The Positive Pacific-Japan Pattern Drives Compound Heat and Dry Extremes in Summer Over Taiwan

This study investigates the role of the Pacific–Japan (PJ) pattern, a dominant mode of the East Asian summer monsoon, in driving compound heatwave–drought events in Taiwan, with a particular focus on land–atmosphere interactions. While the PJ pattern is known for modulating regional rainfall and circulation, its use as a physically interpretable framework to examine dry and warm atmospheric forcing at the land surface remains underexplored for Taiwan. Using a high-resolution 2-km regional reanalysis dataset (TReAD) for Taiwan from 1980 to 2019, we show that the positive phase of the PJ pattern is associated with suppressed rainfall, depleted soil moisture, and more frequent heatwaves. To understand the processes linking these anomalies, we analyze land-atmosphere energy and water exchanges, revealing that soil moisture deficits reduce latent heat flux and increase sensible heat flux—amplifying near-surface temperatures and exacerbating heat extremes. These findings highlight the importance of land–atmosphere coupling in modulating surface climate responses under large-scale meteorological forcing. By connecting predictable large-scale climate modes with local surface processes, this study provides a process-based foundation for using the PJ pattern as a seasonal-scale indicator of compound hot and dry risk in Taiwan. The framework has potential application in early warning and climate risk management, particularly when combined with sub-seasonal to seasonal (S2S) forecast products.