Variations in GPS precipitable water vapor and rainfall during the 2006–2019 Mei-yu season in Taiwan

The Mei-yu season contributes 26.3% of the annual precipitation and provides important water resources to Taiwan. GPS meteorology derives continuous, real-time and high spatial coverage of perceptible water vapor (PWV), which supports weather forecasting for rainfall indicators. This study analyzes the long-term spatial–temporal changes in GPS PWV and rainfall data during the Mei-yu season from 2006 to 2019. The daily average data show that the Mei-yu season extended in recent years. Both daily rainfall and PWV increase in mid-May and rainfall reaches a maximum in early June, while PWV maintains stable in June. The yearly results show that the trend of the accumulated rainfall in the Mei-yu season is flat, and that PWV increases by 13% over 14 years, which may be due to global warming as the trend of temperature increases by 8%. Spatially, PWV is significantly higher in southern Taiwan during the Mei-yu season, and rainfall increased the most in both the central and southern mountain regions.