## 1 Introduction  
Irrigated agriculture is the largest consumer of fresh water, accounting for 70% of worldwide water use [1]. In this sense, water availability in arid and semi-arid regions is the main factor limiting agricultural production. These regions are subjected to water constraints and are particularly vulnerable to climate change. As a direct result, it is expected that there will be an increase in the mean air temperature with severe drought events occurring during the high evapotranspiration demand periods, accompanied by an irregular rainfall pattern during the wet periods [2]. In addition, Spain--the largest fresh fruit producer in the European Union--has been experiencing severe water supply issues in recent decades, caused mainly by a structural imbalance between water resources and demand [3]. With regards to sweet cherry (_Prunus avium_ L.) production, Spain is the seventh-largest producer of cherries in the world and the second-largest producer in Europe [4]. The application of water-saving strategies to this crop, such as deficit irrigation (DI) procedures, should be a priority for their production in areas with water supply issues. Sweet cherry has been described as sensitive to water deficit during the pre-harvest period, when water stress could affect fruit development [5]. However, the application of deficit irrigation in the post-harvest period does not negatively affect yield or fruit size [6, 7]. To achieve this, tree water status indicators play the main role and lead to better decisions in DI application strategies, leading to favorable water management at the farm level. These indicators are measured and calculated by sensors which are critical for the correct application of DI. Midday stem water potential (\(\Psi\)stem) is considered the reference indicator for monitoring plant water status in many woody crops such as sweet cherry trees [8, 9, 10]. Even though its measurement is laborious, destructive and cannot be automated, it has been described as the most accurate, reliable and stable water status indicator in fruit trees [11]. In recent years, other water status indicators have increased in popularity due to their consistent, accurate and non-destructive measurements, that enable the implementation of automatic irrigation systems. Moreover, some of them are associated with lower costs and simple management devices. Infrared thermal sensing has emerged as a powerful technology for monitoring crop water status due to its non-destructive and continuous measurement at an affordable cost and at different scales (from individual plants to complete fields) [12, 13]. The principle of infrared thermography is based on leaf energy balance [14]. The transpiration process involves water evaporation through stomata and has a cooling effect, which decreases the crop canopy temperature (Tc) [13]. The degree of canopy cooling can be used as an indicator of stomatal conductance and transpiration rate, and hence, as a measure of plant response to water status, as severe water stress will produce a stomatal closure and the Tc will increase [15]. However, Tc does not only depend on stomatal aperture but is also determined by weather variables such as solar incident angle, solar radiation, air temperature and wind speed [13, 16]. To normalize the variation and minimize the effect of environmental factors, several thermal indexes were developed and implemented to monitor and quantify water stress. [PERSON] et al. [17] suggested the first index--the difference between the canopy and air temperature Ta (Tc - Ta = \(\Delta\)T). \(\Delta\)T was able to minimize the weather variables; however, it was highly dependent on vapour pressure deficit (VPD). Subsequently, [PERSON] et al. [18] and [PERSON] et al. [19] developed the crop water stress index (CWSI) for establishing stress for crops by determining non-water-stress baselines (NWSB) and non-transpiration baselines (NTB).