Modelling heat and water exchanges of fallow land covered with plant-residue mulch

To document the long-term energy and water budget of a fellow land, a compl ete dataset was collected in the south-west of France. it included climatic data, surface fluxes, vegetation evolution and soil moisture monitoring. T he soil hydrodynamic and thermal properties were also determined in situ an d through laboratory measurements. The experiment was conducted during 3 ye ars (1995-1997) on a 20 ha held. A natural plant-residue mulch layer was co nstantly covering the field. Its thickness artificially increased in June 1 995 when the farmer unexpectedly cut the grass and left the residue on the ground. Two versions of the simple soil plant atmosphere transfer (SiSPAT) model we re compared using the 1995 dataset: the original version which did not take into account the mulch layer; and a modified version where explicit modell ing of the mulch was included (SiSPAT-mulch). The prediction of soil temper ature, surface fluxes and surface soil moisture was improved when consideri ng a mulch layer. Annual surface evaporation was divided by a factor two to four and transpiration increased by 30-50% when considering the mulch laye r. Annual total evaporation decreases by 4-10% according to mulch character istics, leading to a better simulation of the annual and daily water balanc e of the sitz. A sensitivity analysis investigated the robustness of these results and possible causes of inaccuracies on half hour values. (C) 1999 E lsevier Science B.V. All rights reserved.