The aim of this research is to simplify the methodof getting Evapotranspiration
Potentielle (ETP) which forms the limit of water needs for crops . This was using done
some experimental Equation like Turc formula and Thornthwaite formula
(Thornthwa
ite, 1948) compared with the modified Blaney_ Criddle formula
( BlaneyCriddle , 1950) which is considered the basic formula in this research . Also , this
research aims to find a formula enables us to use (Pans evaporation) method (class A) as a
relative evidence to the need of watering in Lattakia by comparing it with the results of
Evapotranspiration Potentielle which are calculated by the modified Blaney _Criddle
method depending on climate data from Lattakia for fifteen years (2001 – 2015) .
The results of studying the correlation coefficient and how the experimental points
spread around the linear regression curve show that Turc gave the best approximaltion
result to the developed Blaney – Criddle formula with correlation coefficient (R=0.907).
After Turc formula there is Thornthwaite formula with correlation coefficient (R=0.846) .
On the other hand Pan class A method gave approximal results to the developed Blaney–
Criddle formula with correlation coefficient (R=0.925) and with good distribution of the
experimental points around the linear regressions straight.
So, in this study experimental conditions it could beased on Turc formula and Pan
class A method as the best approximation to the developed Blaney- Criddle formula to
define the water requirement of the agriculture crops in Lattakia.
