Positive or negative correlation between actual and potential evaporation? Evaluating using a nonlinear complementary relationship model. Issue 2 (18th February 2014)

• Record Type: Journal Article
• Authors: Han, Songjun; Tian, Fuqiang; Hu, Heping
• Is Part Of: Water resources research. Volume 50:Issue 2(2014:Feb.)
• Page Start: 1322
• Page End: 1336
• Publication Date: 2014-02-18
• Subjects: Hydrology -- Periodicals; 333.91
• DOI: 10.1002/2013WR014151
• Languages: English
• ISSNs: 0043-1397

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>Understanding whether a positive or negative correlation between actual (<italic>E</italic>) and potential (<italic>E<sub>p</sub></italic>) evaporation is of great importance in detecting changes of <italic>E</italic> from <italic>E<sub>p</sub></italic>. In this study, such correlation was evaluated via the linear regression slope (<italic>k</italic>) between <italic>E</italic> and <italic>E<sub>p</sub></italic> derived from a nonlinear complementary relationship model. <italic>k</italic> varies with the relative degree of variability in the radiation term (<italic>E<sub>rad</sub></italic>) and aerodynamic term (<italic>E<sub>aero</sub></italic>) of <italic>E<sub>p</sub></italic>, and is further affected by water availability. The sign of <italic>k</italic> is always positive under conditions with high <italic>E<sub>rad</sub></italic> variability but at the same time with low <italic>E<sub>aero</sub></italic> variability (commonly true on an hourly basis). Under conditions with high <italic>E<sub>aero</sub></italic> variability but at the same time with low <italic>E<sub>rad</sub></italic> variability, the sign of <italic>k</italic> tends to change from negative to positive with more readily water availability. On a daily or annual basis, the sign of <italic>k</italic> would be related with water availability. Under water‐limited conditions, the <italic>E<sub>aero</sub></italic> variability is more significant than the <italic>E<sub>rad</sub></italic> variability, and negative <italic>k</italic> is expected. Under energy‐limited conditions, the <italic>E<sub>rad</sub></italic> variability is compared to or even much obvious than the <italic>E<sub>aero</sub></italic> variability, and positive <italic>k</italic> is expected. This implies a negative correlation between <italic>E</italic> and <italic>E<sub>p</sub></italic> under water‐limited conditions but a positive correlation under energy‐limited conditions on the daily or annual basis. The above analysis is confirmed in a grassland site in Northeast China at daily and half‐hourly time scales. The correlation between annual <italic>E</italic> and <italic>E<sub>p</sub></italic> over China was evaluated using data of 690 meteorological stations from 1956 to 2005. The <italic>k</italic> values change from negative in arid regions to positive in humid regions. According to <italic>k</italic> and the decreasing trends in annual <italic>E<sub>p</sub></italic>, it is deduced that <italic>E</italic> increased for most stations in arid regions but decreased for most stations in humid regions.</p> </abstract>