2.3.1. Estimation of Potential Evapotranspiration and Net Irrigation Requirement

Maximum and minimum air temperatures (Tmax and Tmin, ◦C), average relative humidity (RH, %), wind speed (U, m s−1) and solar radiation (Rs,Wm−2) were measured by weather stations located near the study schemes, 10◦54'54.1" N and 0◦49'35.3" W in the BIS, and 10◦50'44.6" N and 0◦54'43.9" W in the VIS. Potential evapotranspiration was calculated based on the Penman–Monteith equation [40]:

$$ET\_0 = \frac{1}{\lambda\_w} \frac{\Delta (R\_{\rm tr} - G) + \rho\_a C\_p (e\_s - e\_a)}{\Delta + \gamma\_a \left(1 + \frac{r\_c}{r\_a}\right)} \tag{1}$$

where *ET*<sup>0</sup> is reference evapotranspiration (mm day−1), *Rn* is net radiation (W m−2), *G* is soil heat flux (W m−2), (*es* − *ea*) is the vapor pressure deficit of the air (kPa), *<sup>ρ</sup><sup>a</sup>* is mean air density at constant pressure (kg m−3), *Cp* is the specific heat of the air (MJ kg−<sup>1</sup> ◦C−1), Δ is the slope of the saturation vapor pressure–temperature relationship (kPa ◦C−1), *λ<sup>w</sup>* is latent heat of vaporization (MJ kg<sup>−</sup>1), *γ<sup>a</sup>* is psychrometric constant (kPa ◦C<sup>−</sup>1), *rc* is crop resistance (s m<sup>−</sup>1), and *ra* is aerodynamic resistance (s m<sup>−</sup>1).

Next, the net irrigation requirement was calculated based on the actual evapotranspiration simulated in AquaCrop as follows [22,41]:

$$NIR = \sum\_{i=1}^{n} \left[ (K\_{cb} + K\_t) ET\_{0\_i} - P\_{c\_i} - CR\_i - W\_{b\_i} \right] \tag{2}$$

where *NIR* is the net irrigation requirement (mm), *n* is the number of days in the crop cycle, *Kcb* is the basal crop coefficient, *Ke* is the evaporation coefficient, *Pe* is effective rainfall (mm), *CR* is capillary rise (mm), and *Wb* is stored soil water (mm).
