Spatial and temporal variations in rainfall characteristics in mountainous and lowland areas in Taiwan

Although changes in rainfall characteristics have been noted across the world, few studies have reported those in mountainous areas. This study was undertaken to clarify spatial and temporal variations in rainfall characteristics such as annual rainfall amount (Pr), mean daily rainfall intensity (η), and ratio of rain days (λ) in mountainous and lowland areas in Taiwan. To this aim, we examined spatial and year-to-year variations and marginal long-term trends in Pr, η, and λ, based on rainfall data from 120 stations during the period 1978-2008. The period mean rainfall (Pr-) at the lowland stations had strong relationships with the period mean daily rainfall intensity (η-) and the period mean ratio of rain days (λ-) during those 31 years. Meanwhile, Pr- was only strongly related to η- at mountainous stations, indicating that influences on spatial variations in Pr- were different between lowland and mountainous stations. Year-to-year variations in Pr at each station were primarily determined from the variation in η at most stations for both lowland and mountainous stations. Long-term trend analysis showed that Pr and η increased significantly at 10% and 31% of the total 120 stations, respectively, and λ decreased significantly at 6% of the total. The increases in Pr were mostly accompanied by increases in η. Although stations with significant η increases were slightly biased toward the western lowland area, increases or decreases in Pr and λ were not common. These results contribute to understanding the impacts of possible climate changes on terrestrial hydrological cycles.