A Study of the Comparison between Evaporation and Precipitation in Taiwan

Author: Yen Huai Liu

Abstract：

This study is based upon the observational data of evaporation and precipitation of the 24 stations in Taiwan during the 10 years period, 1951-1960.
Evaporation: Among the 24 stations Kaohsung had the greatest amount of annual evaporation, 2105.4 mm,. Tawu had the second highest annual evaporation, 2096.9mm. Hengchun had the third highest annual evaporation 1986. 8mm. These 3 stations are located in the tropical southern part of this island. The higher temperature and the stronger wind at these stations are favorable for higher evaporation. The least annual evaporation was found in the mountainous part of northern Taiwan. Mean annual evaporation at Anpu totals 760.4mm, and at Chutzehu totals 883.5mm. Both stations have annual precipitation more than 4000mm. The precipitation is evenly distributed in the monthes of the year. The air is always moist, and so the evaporation is very low. At most of the stations, the highest monthly evaporation was found in the warmest summer month, July. But, some of the stations had the highest evaporation in August. The least monthly evaporation was found in winter month, January, February or December. It is remarkable that at Hengchun the least evaporation was found in August. From 24 stations there are 17 had the highest seasonal evaporation in Summr. 23 stations had their least seasonal evaporation in winter. There are 6 stations with highest seasonal evaporation in Spring and one station Yushan had the highest seasonal evaporation in Autumn.
Precipitation: Among the 24 stations in Taiwan, Chutzehu had the greatest annual precipitation; 4692. 9mm. Anpu had the second highest annual precipitation, 4524.5mm. The least annual precipitation was observed at Penghu, 1064.3mm. On the main island Taiwan, Hsinchu had the least annual precipitation, 1643.3mm. The highest monthly precipitation was found in November at Anpu, Chutzehu, and Chilung. Chilung had its least precipitation in July. At Pengchiayu, Tansui, Yilan, Chinliuchieh, Hualien, Penghu, Hsinkang, September is the month had the greatest precipitation. Taipei had the greatest precipitation in July, Hsinchu in May, Kaohsung in June. August is the month with greatest precipitation at following stations: Taichung, Jihyuetan, Alishan, Lulinshan, Hsinkang, Tainan, Taitung, Tawu, Lanyu, and Hengchun. Stations with least precipitation in January are Tansui, Hualien, Yushan, Yungkang, Tainan and Tawu. Stations with February as month of least precipitation are Hsinkang, Taitung and Kaohsung. Stations with November as month of least precipitation are Jihyuetan and Alishan. Taipei, Penghu and Lulinshan had December as the month with least precipitation. Among the 24 stations only at Chilung winter was the most rainy season and Summer had the least rainfall. Stations with Summer as the most rainy season are Taipei, Taichung, Jihyuetan, Penghu, Alishan, Lulinshan, Yushan, Yungkang, Tainan, Taitung, Kaohsung, Tawu and Hengchun. Stations with Autumn as the most rainy season are: Pengc-hiayu, Anpu, Chutzehu, Tansui, Yilan, Chinliuchie, Hualien, Hsinkang and Lanyu. Hsinchu had Spring as the most rainy Season.
Comparison: The annual evaporation at Penghu is 822.7 mm more than the annual precipitation, and so Penghu had the most dry climate among the 24 stations in Taiwan. But, Penghu had 2 wet monthes August and September with more rainfall than evaporation. Kaohsung and Yungkang had also less annual precipitation than annual evaporation and the rainfall concentrated in Summer. June, July, August and September were the 4 monthes more precipitation than evaporation. Anpu, Chutzehu, Lulinshan and Lanyu had no month with less precipitation than evaporation. At Anpu Chutzehu, Chilung, Taipei, Yilan, Chinliuchie, Lulinshan and Lanyu, all the 4 seasons had more precipitation than evaporation. Even at Kaohsung and Yungkang where the annual precipitation is less than the annual evap-oration, had a rainy Summer with more rainfall than evaporation.
Taiwan is located in the tropical and subtropical belt, and dominated by the NE monsoon in winter and SW monsoon in summer. Most of the stati-ons in Taiwan have rainfall in summer and dryness in winter. All the stations on the island Taiwan have annual precipitation more than 1600mm. The annual rainfall in the mountainous erea is still more, and at some place more than 4000mm, and at some locality annual rainfall of more than 6000 and 8000mm were reported. The mountains of the Central Range rise in the middle of the island from north to south. The distance between the mount-ain and sea is very short and the slope of the land is quite steep. Rainfall in Taiwan is well plenty, but the rain water flows down rapidly to the sea. So, one can understand how necessary it is to prevent the outflow of the rain water into the sea. In recent years, some water reservoir were conpl-eted to preserve the rain water for irrigation and powerplant in dry seasons. The efficiency of these reservoirs is still limited, and more reservoirs should be constructed. In the tropical and subtropical climate like Taiwan, 3 crops yearly could be achieved, the only problem is water. We need to prevent the outflow of the rain water and reserve it for use.

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