Forecasting Irrigation Shifts in Fruit Cultivation Under Climate Change Scenarios in Tropical Thailand

Abstract

Irrigation management in tropical fruit orchards is most difficult during the tran- sition from the dry to the wet season, when atmospheric demand is high and rain- fall is erratic. This study presents a web-based decision-support framework that converts hourly meteorological records into irrigation requirements and evalu- ates how they shift under climate perturbation. Vapor pressure deficit (VPD) and hourly reference evapotranspiration (ETo) are computed with the FAO-56 Penman-Monteith equation, scaled by stage-specific crop coefficients and con- verted to a per-tree volume using canopy radius. The implementation reproduces the worked hourly values of FAO-56 Example 19 exactly. For a representative day in Chanthaburi, Thailand, the net requirement for durian rose from 3.53 to 7.05 liters per day for a tree of 1.0 m canopy radius under a perturbation of +2 ◦C and −20% relative humidity. Because this result depends on how hu- midity is assumed to respond to warming, the calculation was repeated under three assumptions which gave increases in mean VPD of between 12.1 and 69.9 percent and in ETo of between 4.8 and 20.4 percent. The direction of the shift is therefore robust while its magnitude is assumption-dependent and irrigation requirements are reported as a range rather than a single value.