Taiwan is located on the eastern edge of the Asia Continent, off the China mainland, southeast of the main islands of Japan, and north-northwest of the Philippines. It borders in the east by the Pacific Ocean, in the north by the East China Sea, to the west by the Taiwan Strait, and to the south by the South China Sea and Bashi Channel. Approximately 70% of its total area of about 36,000 km2 is mountainous, mainly lying in the central region stretching from north to south which forms the ridges of the majority of the island’s rivers. The remaining 30% of the land is mostly the plains and mild sloping lands with elevations below 100m, mainly spreading in the western corridor and along both banks of rivers.
In the plain areas, the average annual temperature is as warm as about 23.9 °C. The average temperature in the warm season (June-September) is about 27-29 °C. In the cool season (November-March), it is around 18-22 °C. The yearly rainfalls in Taiwan between 1949 and 2020 range from 1,572 to 3,241 mm, or about 90 billion cm3 in volume, equivalent to about 2.1 times the world’s average. Taiwan, accordingly, is categorized as a region of abundant rainfall.
Each year, about 78% of the island’s rainfalls occur between the wet season of May and October mainly sourced by plum rains, storms, and typhoons. And during the months of dry seasons, the total rainfall amount is just around 22% of the yearly sum. Amounts of annual rainfall vary drastically, and the hydrological uncertainties in Taiwan are quite acute.
