DETERMINATION OF POTENTIAL AND ACTUAL EVAPOTRANSPIRATION IN WATERSHED, USING MATHEMATICAL MODELS DETERMINACIÓN DE LA EVAPOTRANSPIRACIÓN POTENCIAL Y REAL EN CUENCA HIDROGRÁFICA, UTILIZANDO MODELOS MATEMÁTICOS

In this research, it is analyzed the calculation of real evapotranspiration in hydrographic basins, it is taken as a reference the Aguablanca Creek, located in the municipality of Bochalema, North of Santander-Colombia, where it is evaluated the hydrologic balance of this basin from the determination of detailed calculations of four mathematical models, to later evaluate the hydrologic balance of this basin, with the purpose of being able to make a better administration of these resources, as well as the use of the soil, betting on the development of an ecologically sustainable society with low environmental impact. The values of potential and real evapotranspiration, according to the most optimal model ETP Thorwaite 874 mm/year ETR 43712 mm/year, Cenicafe 712.81 mm/year ETR 612.1 mm/year Turc ETR 884.83 mm/year quota ETR 825 mm/year.

However, these are not the only variables.
Thorwaite's potential evapotranspiration equation is: (1) Where: Tm is the average monthly temperature in C I : annual heat index I = Summation ( ij ) ; j = 1, ..., 12 (which is calculated by adding the twelve monthly heat indexes).
ij = (tmj/5) 1.514 a : parameter that is calculated from I according to the expression: (2) a = 0,000000675× I 3 -0,0000771× I 2 + 0,01792× I + 0,49239 (1) And finally we have to: (4) Where: (5) In the Turc model, a mass balance is established, resulting in the following expression: Where, ETR, is the actual evapotranspiration (mm/year), P is the average precipitation of the basin during one year (mm/year) and T is the average annual temperature in ºC.
When the P/L ratio > 0.316, equation 6 is used where L is represented by the following equation: If P/L < 0.316, then ETR=P.

Turc Model
In the Turc model, a mass balance is established, resulting in the following expression: When the P/L ratio > 0.316, equation 6 is used where L is represented by the following equation: = 300 + 25 + 0.05 3 If P/L < 0.316, then ETR=P.

Turc Model
In the Turc model, a mass balance is established, resulting in the following expression: When the P/L ratio > 0.316, equation 6 is used where L is represented by the following equation: = 300 + 25 + 0.05 3 If P/L < 0.316, then ETR=P.

Turc Model
In the Turc model, a mass balance is established, resulting in the following expression: When the P/L ratio > 0.316, equation 6 is used where L is represented by the following equation: = 300 + 25 + 0.05 3 If P/L < 0.316, then ETR=P.

Turc Model
In the Turc model, a mass balance is established, resulting in the following expression: When the P/L ratio > 0.316, equation 6 is used where L is represented by the following equation: = 300 + 25 + 0.05 3 If P/L < 0.316, then ETR=P.

Turc Model
In the Turc model, a mass balance is established, resulting in the following expression: When the P/L ratio > 0.316, equation 6 is used where L is represented by the following equation: = 300 + 25 + 0.05 3 If P/L < 0.316, then ETR=P.
This model is based on the meteorological conditions of the basin. Where an estimation of the real evapotranspiration is made as a function of the precipitation and the temperature of the: Where ETR is the actual evapotranspiration in mm/year and P is the precipitation in mm/year.
The lambda factor is a temperature-dependent factor. (10) T is the value of the average annual temperature in Cº. Equation 9 is only applicable for P values between (8λ) -1 and (2λ) -1 . If rainfall is less than (8λ) -1 then:

III. Results and Discussions
3.1 Thorwaite model. The results of equations 2, 3 and 5 are in the following tables: The total value of I is given by the sum of all the (8) The values of actual evapotranspiration would be of the order: The factor L in equation 5 is now calculated from the data in Table 1.  The values corresponding to (8λ)-1 and (2λ)-1 equal to 0.438 and 1.754 expressed in meters, and the precipitation is equal to 1327.9 mm or 1,327 m, therefore, it is in the range.
Actual evapotranspiration is calculated as defined by equation 10.

IV. CONCLUSION
The calculation of the real evapotranspiration is one of the most important parameters to establish the water balance of a basin, in this case of study, the basin of the Aguablanca stream located in the municipality of Bochalema, Norte de Santander, Colombia.
The values of potential and actual evapotranspiration, according to the model are.