University of Twente Student Theses


Tree transpiration, a spatio-temporal approach in water limited environments – Sardon study case

Ontiveros Enríquez, Ricardo (2009) Tree transpiration, a spatio-temporal approach in water limited environments – Sardon study case.

[img] PDF
Abstract:Tree transpiration (Tt) has a significant role in the water balance of a catchment whenever it is tree populated, especially in water-limited environments (WLE). In this balance, it is an important component of the ET flux and is usually underestimated when assessing for water resources due to measurement difficulties and high spatio-temporal variability. In some cases, Tt has a water uptake contribution in both, the unsaturated and the saturated zone, as some plant species have phreatophyte behaviour. This study aims to provide a spatiotemporal approach for tree transpiration flux evaluation in the Sardon catchment, a representative WLE. The methodology proposed focuses on the assessment of Tt of the two tree species that grows in the area, deciduous Quercus pyrenaica (Q.p.) and evergreen phreatophyte Quercus ilex (Q.i.) and their spatio-temporal upscaling. The species-specific flux patterns of transpiration were defined by assessing sap flux density (ν) of individual trees in different seasons using thermal dissipation probe (TDP) method. The transpiration of individual trees (Tt) was estimated by sap flow (Qs) defined as product of ν and xylem area (Ax). Ax was measured on field for tree size distributed species and then upscaled to stand transpiration (T) for spatial approach by applying species-specific biometric upscaling function (BUF). The ν was used for assessing temporal variability of Tt. Spatio-temporal variability of T was evaluated on the temporal base of representative days in climate contrasting seasons and in the spatial base of homogeneous and heterogeneous species stands. The model applied to simulate temporal variability uses two environmental factors: incoming solar radiation (Rin) and relative humidity (RH). Additionally, the use of PET was proposed as a modified version of that model for particular assessment of Tt in WLE. While analyzing sensitivity of these models, hysteresis response was observed and enhanced whenever adding the PET component. The calibrated model allowed the extrapolation of v over a five year period, from 2003 to 2008. An approach on seasonal spatio-temporal variability of tree stand transpiration is evaluated for both heterogeneous and homogeneous stands and a general attempt to upscale T for the Sardon catchment during the given period is presented.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
Link to this item:
Export this item as:BibTeX
HTML Citation
Reference Manager


Repository Staff Only: item control page