Revealing the intricate relationship: Droughts and typhoons in Taiwan using the Standardized Precipitation Index (SPI)

Study region: Taiwan Study focus: This study examines the relationship between typhoon parameters and droughts in Taiwan, particularly following the severe drought of 2020-2021. Using tropical cyclone best- track and satellite-based precipitation datasets from 1981 to 2020, we analyzed anomalies, correlation matrices, and wavelet coherence. Seasonal variations and long-term trends were also detected. New hydrological insights for the region: We found a positive correlation between typhoon characteristics (count, duration, length, wind speed) in Taiwan and drought occurrence and severity, especially over 2-4 year periods. Conversely, negative relationships were observed between typhoon duration and length in the Western North Pacific (WNP) and drought indices in Taiwan, influenced by large-scale atmospheric patterns. Typhoon duration and length in the WNP had a greater impact on Taiwan's drought than typhoon quantity, showing significant coherence with long-term drought over multi-year to decadal timescales. Seasonally, drought intensity peaked in central and southeastern Taiwan during late winter and early spring when typhoons were absent, in contrast to the rainy summer typhoon season. Spatially, increasing drought trends were identified in central and southern Taiwan, while northern regions exhibited decreasing dryness, potentially linked to the concentration of typhoon landing points in the north. This study underscores the complex relationships between drought severity in Taiwan and typhoon behavior in both the vicinity of Taiwan and the WNP.