This investigation has permitted us to come to the conclusion that the INSTAT+3.37 and CROTWAP8.0 methods of computation of the evapotranspiration are coherent in Guinea Bissau. Therefore, they can be quietly introduced in operative works in the country. The best period of cultivation period is very short in Bafata, approximately 50 days. Consequently, irrigation is unavoidable there as the vegetative cycle of many agricultural species is around 90 days.