*3.1. Performance of the Smart ET-Based Controller*

The Weathermatic controller overestimated ETo by 5–7% in 2018 and by 5–8% in 2019 compared with CIMIS ETo values. On average, across all treatments, MAE was 2.8 mm day <sup>−</sup><sup>1</sup> (4% ETo) and 2.9 mm day <sup>−</sup><sup>1</sup> (5% ETo) in 2018 and 2019, respectively. We ran a flow test at the end of the trial, which revealed that the actual precipitation rate of the irrigation system was 28 mm h−1, 21% higher than the 23 mm h−<sup>1</sup> precipitation rate initially estimated using the catch-cans. Consequently, the applied irrigation was recalculated using the irrigation run time data recorded by the controller for the duration of the experiment, as listed in Table 2. The adjusted irrigation levels varied between 83% and 129% of ETo for the tall fescue plots and between 65% and 101% of ETo for the hybrid bermudagrass treatments.

**Table 2.** Target irrigation treatments (T1–T3) versus programmed and applied irrigation levels for tall fescue and hybrid bermudagrass irrigation research experiments.


Programmed irrigation levels are equal to target treatment levels divided by the irrigation efficiency of 0.78 (i.e., the low half distribution uniformity of the irrigation system). Applied irrigation levels were recalculated based on the irrigation run time data retrieved from the controller and precipitation rate of 28 mm day−<sup>1</sup> measured for the system at the end of the trial.

The controller closely followed programmed watering days restrictions across treatments in 2018 and 2019. For the 7 d wk−<sup>1</sup> treatment (no frequency restriction scenario) in 2019, the controller adjusted the actual irrigation days based on the evaporative demand and minimum allowed water deficit. For example, on average, plots were irrigated five days per week for 65% ETo irrigation treatment with no frequency restriction.

Figure 3 depicts the performance of the Hargreaves and Samani equation [17] against CIMIS ETo based on the long-term data (1983–2019) obtained from the CIMIS station #39. Overall, there was a strong agreement between the ETo values obtained using the Hargreaves and Samani [17] and CIMIS methods, as depicted by high correlation (*r* = 0.96) and well-scattered data points around the identity line (1:1). The MAE between Hargreaves and Samani and CIMIS ETo varied between 0 and 3.98 mm day−<sup>1</sup> with an average value of 0.55 mm day−1. The mean annual MAE values fluctuated over the years between 0.4 mm day−<sup>1</sup> and 0.8 mm day−1. The MAE values were relatively higher in peak ETo months (i.e., May to September) than during the rest of the year.

**Figure 3.** Scatter plot of ETo estimated using the Hargreaves and Samani (HS) [17] versus CIMIS values (**a**) and variation in long-term annual and seasonal mean absolute error (MAE) values (**b**). MAE shows the difference between the HS and CIMIS models and the red horizontal line in figure (**b**) represents the mean MAE.
