Robusta coffee production in Vietnam's Central Highlands relies heavily on irrigation, raising concerns about water resource depletion. As climate change increases the likelihood of prolonged dry seasons, there is an increasing need to understand crop water use in order to tailor irrigation practices and enhance the resilience of coffee systems. This study investigates the transpiration dynamics and productivity of Robusta coffee under two cropping systems (monoculture and agroforestry) and two irrigation regimes (high: 133 mm yr-1 vs. low: 83 mm yr-1) in a split-plot field trial. Transpiration was monitored from January 2023 to July 2024 on 24 coffee trees using sapflow sensors, and compared with reference evapotranspiration (ETo) to estimate monthly basal crop coefficients (Kcb). Leaf water potential was measured before each irrigation event to assess plant water status. Finally, coffee yield and physical quality were monitored over three years (2022–2024). Interestingly, this trial offers insights into contrasted climatic conditions, with a normal dry season in 2023 and an extreme dry season in 2024. Results show that during normal conditions (dry season 2023), irrigation could be reduced by 40% without negatively affecting transpiration, yield, or quality. However, under extreme drought (dry season 2024), reduced irrigation was insufficient to sustain tree transpiration and yield in the monoculture system. In agroforestry systems, coffee trees transpired on average 33% less than in monoculture, allowing for a reduction in irrigation even under extreme drought. The corresponding Kcb values ranged from 0.55 to 0.85 in monoculture and from 0.36 to 0.57 in agroforestry systems. While coffee trees under agroforestry demonstrated greater resilience to prolonged dry seasons, their yield was overall 18–33% lower than in monoculture. These findings highlight the potential of agroforestry to buffer drought impacts and contribute new Kcb values for Robusta coffee. They sup