@article{fdi:010042151,
  title = {{C}omparison of root water uptake modules using either the surface energy balance or potential transpiration},
  author = {{B}raud, {I}. and {V}arado, {N}. and {O}lioso, {A}.},
  editor = {},
  language = {{ENG}},
  abstract = {{N}umerical models simulating changes in soil water content with time rely on accurate estimation of root water uptake. {T}his paper considers two root water uptake modules that have a compensation mechanism allowing for increased root uptake under conditions of water stress. {T}hese modules, proposed by {L}ai and {K}atul and {L}i et al. [{A}dv. {W}ater {R}esour. 2.3 (2000) 427 and {J}. {H}ydrol. 252 (2001) 189] use potential transpiration weighted, for each soil layer, by a water stress and a compensation function in order to estimate actual transpiration. {T}he first objective of the paper was to assess the accuracy of the proposed root extraction modules against two existing data sets, acquired under dry conditions for a winter wheat and a soybean crop. {I}n order to perform a fair comparison, both modules were included as possible root water extraction modules within the {S}imple {S}oil {P}lant {A}tmosphere {T}ransfer ({S}i{SPAT}) model. {I}n this first set of simulations. actual transpiration was calculated using die solution of the surface energy budget as implemented in the {S}i{SPAT} model. {U}nder such conditions, both root extraction modules were able to reproduce accurately the time evolution of soil moisture at various depths, sod water storage and daily evaporation. {R}esults were generally improved when we activated the compensation mechanisms. {H}owever. we showed that {L}ai and {K}atul [{A}dv. {W}ater {R}esour. 23 (2000) 427] module was sensitive to soil hydraulic properties through its water stress function, whereas the {L}i et al. [{J}. {H}ydrol. 252 (2001) 189] module was not very sensitive to the specification of its parameter. {T}he latter module is therefore recommended for inclusion into a larger scale hydrological model, due to its robustness. {W}hen water balance models are run at larger scales or on areas with scarce data. actual transpiration is often calculated using. models based on potential transpiration without solving the surface energy balance. {T}he second objective of the paper was to assess the loss of accuracy in such conditions for the {L}ai and {K}atul and {L}i et al. [{A}dv. {W}ater {R}esour. 2.3 (2000) 427 and {J}. {H}ydrol. 252 (2001) 189] modules. {F}or this purpose we compared results from the {S}i{SPAT} model solving the surface, energy balance with those of a degraded version where only potential evapotranspiration was imposed as input data. {W}e found that actual transpiration and evapotranspiration were in general underestimated, especially for the {L}ai and {K}atul [{A}dv. {W}ater {R}esour. 23 (2000) 427] module. when we used the potential evapotranspiration as calculated from {FAO} standards. {T}he use of crop coefficients improved the simulation although standard values proposed by the {FAO} were too small. {T}he definition of the potential evapotranspiration was the major source of error in simulating soil moisture and daily evaporation rather than the choice of the root extraction modules or the inclusion of a compensation mechanism. {W}hen used for water management studies, a sensitivity to the definition of potential evapotranspiration used to run the models is therefore advisable. ({C}) 2004 {E}lsevier {B}.{V}. {A}ll rights reserved.},
  keywords = {compensation ; root extraction ; water stress ; {SVAT} ; potential evapotranspiration ; energy balance},
  booktitle = {},
  journal = {{J}ournal of {H}ydrology},
  volume = {301},
  numero = {1-4},
  pages = {267--286},
  ISSN = {0022-1694},
  year = {2005},
  DOI = {10.1016/j.jhydrol.2004.06.033},
  URL = {https://www.documentation.ird.fr/hor/fdi:010042151},
}