Source: https://orbi.uliege.be/jspui/bitstream/2268/131407/1/Traor%C3%A9%202007%20-%20M%C3%A9thodes%20d%E2%80%99estimation%20de%20l%E2%80%99%C3%A9vapotranspiration%20r%C3%A9elle.pdf