History of Irrigation in Taiwan

Part I: Natural Environment of Taiwan

  1. A. Topography and Rivers
  2. Taiwan is an island with total area of 36,000 km2. Approximately 70% of the island is covered by mountains that mainly lying on along the central region running north to south and thus forming a ridge for the east- and west-bound rivers, and the rest 30% is the plains below the elevation of 100 m.

    There are altogether 151 rivers in Taiwan, but only nine of them each possess a basin area exceeding 1,000 km2. As regards to riverbed slopes, those of the upstream reaches of most rivers exceed 1/100, and of the downstream are between 1/200 to 1/500, among them only five rivers with slope below 1/1,000. The sediment yield per unit area of the rivers in Taiwan is about 64 times of the world average and the sediment concentration is about 16 times of the world average.

    Taiwan Map

  3. B. Climate and Rainfall
  4. Overlying both subtropical and tropical oceanic zones and situated in the Asian monsoon region, Taiwan features warm climate, the annual average temperature in the plain areas is as high as 22°C; even thelowest temperatures in a year stay above 10°C.

    The rainfall in Taiwan is approximately 2,500 mm annually, which is about 2.6 times that of the world average. Owing to the dense population on this island, however, the average precipitation share per capita amounts to only 3,913 m3 per year, which is less than one eighth of the world average. Hence, it is appropriate to say that Taiwan is among the regions where the potential for water-resource is categorized as low. Statistics further show that there have been huge differences of rainfall distributions among seasons in Taiwan, with the highest annual total rainfall of 3,250 mm, and the lowest, 1,600 mm. The annual evaporation by regional amount is approximately 1,250 mm in the northeast, 1,600 mm in the west, 2,000 mm in the south, and 1,700 mm in the east, and the highest evaporation rate occurs in July.