## 2 Materials and Methods
### Field Data  
Meteorological variables were collected by two weather stations of the Agricultural Information System of Murcia (CA52 for Plot 1 and JU42 for Plot 2; SIAM, [[http://siam.imida.es/](http://siam.imida.es/)]([http://siam.imida.es/](http://siam.imida.es/))). Daily reference crop evapotranspiration (ET\({}_{0}\)) was estimated using the Penman-Monteith equation and daily mean air vapour pressure deficit (VPD) using air temperature and relative humidity data [27]. Additionally, in Plot 1, three microclimate sensors (ATMOS-14, METER Group Inc., Pullman, WA, USA) were installed. The ATMOS-14 sensors were connected to a datalogger (CR1000 with AM16/32B multiplexer, Campbell Scientific Ltd., Logan, UT, USA), programmed to take measurements every 30 s and report mean values every 10 min. In both experiments, every 2-5 days in Plot 1 and 10-15 days in Plot 2, midday stem water potential (Tstem) was measured at solar noon (12:00 to 13:00 UT) with a Scholander-type pressure bomb (mod. SF-PRES-70, SolFranc Tecnologias, S.L., 43480 Tarragona Spain) following the recommendations of [PERSON] and [PERSON] [30]. **V**stem was measured in 2 mature leaves per replicate (6 leaves per treatment). The mature and healthy leaves, close to the trunk, were enclosed in small black plastic bags and covered with aluminium foil for 2 h before the measurement. The canopy temperature (Tc) was measured at the same time as **V**stem with a low-cost thermal camera (ThermalCam Flir One, Flir Systems, Wilsonville, OR, USA) connected to a smartphone. Two images per replicate (n = 6) were taken at 1.5 m from the sunny side of the trees in order to identify the highest differences between irrigation treatments, according to [PERSON] et al. [31] and [PERSON] [13]. The camera uses a thermal sensor with a spectral range of 8-14 \(\upmu\)m and 80 \(\times\) 60 pixels, and a visible-light sensor of 1440 \(\times\) 1080 pixels with \(\pm\)2% precision. The emissivity, \(\varepsilon\), was set at matt (\(\varepsilon\) = 0.95), as suggested by [PERSON] and [PERSON] [32] and [PERSON] et al. [31]. The images were analyzed using the Flir Tools application (Flir One, Flir Systems, Wilsonville, OR, USA). The Tc average of four sunny areas was selected within the same image (24 areas per treatment; Figure 1). The distance of the camera from the canopy, the background temperature, relative humidity and air temperature were used as input to discard the effect of reflection by the object's surface and the radiation emitted by the object's surroundings, according to the methodology proposed by [PERSON] [33] and [PERSON] [22]. Three thermal indices were calculated to mitigate the effect of meteorological variables: (i) The difference between the canopy and air temperature (\(\Delta\)T); (ii) crop water stress index (CWSI), calculated following the recommendation by [PERSON] et al. [19]; and (iii) the degree above control treatment (DAC) and degree above non-water-stressed baseline (DANS) were calculated according to [PERSON] et al. [15]:  
\[\Delta\mathrm{T}=\mathrm{Tc-Tair}, \tag{1}\]  
\[\mathrm{CWSI}=\frac{\Delta\mathrm{Tc-\Delta T_{wet}}}{\Delta\mathrm{T_{dry} -\Delta T_{wet}}}, \tag{2}\]  
\[\mathrm{DAC}=\mathrm{T_{S}-T_{CTL}}, \tag{3}\]  
\[\mathrm{DANS}=\mathrm{T_{c}-(Tair+\Delta T_{wet})}, \tag{4}\]  
where Tc is the canopy temperature; Tair is the air temperature at the moment of the measurement; T\({}_{S}\) is the canopy temperature of the water-stress treatment; T\({}_{CTL}\) is the canopy temperature of the control treatment; \(\Delta\mathrm{T_{wet}}\) and \(\Delta\mathrm{T_{dry}}\) are the differences between canopy and air temperature when the crop has the stomata fully transpiring and fully closed, respectively. According to [PERSON] et al. [18]\(\Delta\mathrm{T_{wet}}\) was calculated from non-water-stress baselines (NWSB; \(\Delta\mathrm{T_{wet}}\) = a + b-VPD).