Forest transpiration in Brazilian drylands: measurement and validation of a hydrological model

Transpiration, particularly in dryland forests, plays a major role in the water cycle. The one-million km 2 Caatinga Biome is a data-scarce region in the Brazilian Semiarid, where rainy and dry season are clearly distinct. This work aims to measure the natural Caatinga vegetation transpiration using sap flow monitoring (between Feb 2016 and Dec 2017) and to validate the hydrological Distributed Catchment Scale Model (DiCaSM). Measured transpiration in situ was on overall average 0.58 mm.day −1 for rainy and transition seasons. There is evidence that sap flow does not provide a good representation of transpiration in dry seasons: sap flow is high, whereas, according to the Literature, actual evapotranspiration is negligible (<0.01 mm.day −1 ) due to a very low soil water content, and, thus, transpiration should also be negligible. Transpiration estimated by DiCaSM presented a well-defined seasonal variability, with values close to zero during the driest months, in agreement to previous literature. Overall, the findings contribute to better expertise regarding the transpiration rates in a dryland environment and may be used in water resources management contexts, as the transpiration process gives insight into local water use and availability. • Two years of sap flow transpiration measurement have allowed seasonal assessment. • There is evidence that sap flow does not represent transpiration in the dry season. • The hydrological model was proved valid for transpiration estimation.