Long-term pan evaporation trend and preliminary investigation of evaporation complementarity in taiwan

Shien Tsung Chen, Yi Hsin Li

Research output: Contribution to journalArticlepeer-review


Under global warming, the evaporation is expected to increase as the temperature increases. However, pan evaporation data over the past 50 years show a decreasing trend in many places. This has recently been discussed, and is termed the “pan evaporation paradox.” Pan observations during recent two decades in Taiwan also exhibit a decreasing trend. Although long-term pan evaporation data are available and the recording periods of some stations are more than 100 years, no long-term trend analysis of pan evaporation data has been studied in Taiwan. This is because that long-term pan evaporation data in Taiwan are not homogeneous in data properties. This inhomogeneity in long-term data is due to the use of different evaporation pans in the early time (20-cm pan) and the modern time (Class A pan). The observations from the 20-cm pan are usually greater than those from the Class A pan in the magnitude of as large as 50 mm/month in Taiwan. This study developed a data reconstruction model by using support vector machines to homogenize the long-term evaporation data from the two evaporation pans. Mann-Whitney-Pettitt method was used to detect the trend of long-term pan evaporation data. Analytical results reveal that, except for one station, the long-term pan evaporation trend in Taiwan exhibits an increasing trend in the north and a decreasing trend in the south. Preliminary analysis of the evaporation complementary relationship in Taiwan was also discussion. Using the precipitation as a variable to explain the environmental wetness, the evaporation complementary relationship can be demonstrated in Taiwan.

Original languageEnglish
Pages (from-to)12-28
Number of pages17
JournalJournal of Taiwan Agricultural Engineering
Issue number1
Publication statusPublished - 2016 Mar

All Science Journal Classification (ASJC) codes

  • General Agricultural and Biological Sciences
  • General Engineering


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