Effect of water temperature on the performance of emitters in drip irrigation

Water temperature can vary during drip irrigation operation and may affect emitter hydraulic performance, although current standards define nominal discharge at a reference temperature of 23 ± 3 °C and do not account for thermal variability. This study evaluated the effects of water temperature on pressure-compensating (PC) and turbulent-flow (T) drip emitters under controlled laboratory conditions. Six commercial emitter models (four PC and two T) were tested at 15, 23, and 33 °C and operating pressures from 50 to 400 kPa following UNE-EN ISO 9261:2010 procedures. Emitter discharge, pressure–discharge relationships, and hysteresis were analysed using linear mixed-effects models (LMM) and nonlinear regression. Water temperature significantly affected emitter discharge (p < 0.05), with contrasting responses between emitter types. T emitters showed a consistent reduction in discharge with increasing temperature. In contrast, PC emitters exhibited model-dependent responses, with some emitters increasing and others decreasing discharge as temperature increased, indicating changes in compensation behaviour. Temperature also modified the pressure–discharge parameters k and x, particularly in PC emitters, suggesting reduced compensation stability at higher temperatures. Hysteresis during pressure ramp cycles was observed only in PC emitters, reflecting the delayed response of the compensation membrane. Although discharge variations were generally small, water temperature influenced emitter hydraulic performance and may affect hydraulic evaluation, system design, and irrigation uniformity under field conditions. These findings support the inclusion of temperature effects in the assessment and selection of drip irrigation emitters.