Transpiration Prediction

Abstract

Management of water resources, especially under arid conditions predicted to result from climate change, will be become more critical in the future. Currently water loss from crop canopies is often estimated using an energy balance approach, e.g., the Penman-Monteith equation. However, there are several difficulties in this approach including accurately accounting for temporal variability in the inputs and the use of crude approximations to quantify some of the variables. Ultimately, the calculation is an empirical exercise as ‘guesstimates’ are required for an undefined crop coefficient with which to make adjustments in the energy balance output. An alternative to the energy balance approach, is the use of a mechanistic derivation that explicitly defines crop yield as a function of transpiration based on up-scaled leaf gas exchange equations. An input in estimating transpiration rate is crop radiation use efficiency, which is generally well documented for individual crop species. Tracking of plant stresses can allow adjustments of radiation use efficiency when stresses causing decreases in radiation use efficiency develop. Hence, crop transpiration can be calculated from well-defined, basic variables accounting for key processes determining plant transpiration rate.