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Table 3

Methods of estimating PET

ClassificationEstimation methodsEstimation formulaInitial value
Methods based on temperature Blaney & Criddle (1950)   k = 0.87 
Linacre (1977)   m = 500 
 
Kharrufa (1985)   a = 0.34,
b = 0.55 
Hamon (1961)    
  
Methods based on mass-transfer Rohwer (1962)   c = 0.44 
Penman (1948)   d = 0.35 
Methods based on radiation Priestley & Taylor (1972)   f = 1.26 
Makkink (1957)   g = 0.61 
Abtew (1996)   K = 0.53 
Hargreaves (1975)   n = 0.0135 
Doorenbos & Pruitt (1977)    
Jensen & Haise (1963)    
ClassificationEstimation methodsEstimation formulaInitial value
Methods based on temperature Blaney & Criddle (1950)   k = 0.87 
Linacre (1977)   m = 500 
 
Kharrufa (1985)   a = 0.34,
b = 0.55 
Hamon (1961)    
  
Methods based on mass-transfer Rohwer (1962)   c = 0.44 
Penman (1948)   d = 0.35 
Methods based on radiation Priestley & Taylor (1972)   f = 1.26 
Makkink (1957)   g = 0.61 
Abtew (1996)   K = 0.53 
Hargreaves (1975)   n = 0.0135 
Doorenbos & Pruitt (1977)    
Jensen & Haise (1963)    

is the reactant influence coefficient; p is the percentage of daytime hours as a percentage of the daytime hours; is the dew point temperature (°C); h is the site elevation (m); A is the latitude (°), where the site is located, it is the daytime duration (h); is the saturated water vapour density term; is the short-wave radiation (MJ/(m2d)); in the Doorenbos & Pruitt (1977) formula, ; is the temperature constant, this study considers −3 °C; removes the selected parameters that need to be adjusted (experience coefficients are not explained), and other symbols have the same meaning as formula 3.

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