The law of reference crop evaporation's variation with time series in Yulin
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DOI:10.7606/j.issn.1000-7601.2010.01.08
Key Words: Yulin  FAO-Penman-Monteith method  reference crop evaporation  time series
Author NameAffiliation
ZHAO Lu Key Laboratory of Arid Agricultural Soil and Water Engineering of Ministry of Education Northwest A & F University, Yangling, Shaanxi 712100, China 
CAI Huanjie Key Laboratory of Arid Agricultural Soil and Water Engineering of Ministry of Education Northwest A & F University, Yangling, Shaanxi 712100, China 
WANG Jian Key Laboratory of Arid Agricultural Soil and Water Engineering of Ministry of Education Northwest A & F University, Yangling, Shaanxi 712100, China 
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Abstract:
      According to 22-year weather data from 1985 to 2006 from five selective weather stations in Yulin, FAO-Penman-Monteith method was adopted to calculate the monthly reference crop evaporation(ETo) in every station, and to analyze the law of ETo′s variation with time series. It can be drawn that the sum of ETo in May, June and July in the five stations accounted for the largest proportion of the whole year. After 1996, the ETo in every station showed a trend of inc rease, which was very significant. From 1985 to 1996, the ETo in Dingbian and Hengshan stations showed a significant decreasing trend with time; and the ETo in Suide, Yuyang and Shenmu stations showed a significant increasing trend, however, the slope of the increase trend line was less than the slop of trend line after 1996. In Yulin, the ETo had a significant positive correlation with the average temperature, sunshine hours and wind speed, while the relative humidity had a significant negative correlation. ETo and high temperature were in positive correlation; Apart from Dingbian, in other stations the minimum temperature had a significant negative correlation with ETo. The average temperature is the main reason for ETo′s change in Yulin from 1985 to 2006.