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 complete dataset was collected in the south-west of France. it included climatic data, surface fluxes, vegetation evolution and soil moisture monitoring. The soil hydrodynamic and thermal properties were also determined in situ and through laboratory measurements. The experiment was conducted during 3 years (1995-1997) on a 20 ha held. A natural plant-residue mulch layer was constantly covering the field. Its thickness artificially increased in June 1995 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 were compared using the 1995 dataset: the original version which did not take into account the mulch layer; and a modified version where explicit modelling of the mulch was included (SiSPAT-mulch). The prediction of soil temperature, surface fluxes and surface soil moisture was improved when considering a mulch layer. Annual surface evaporation was divided by a factor two to four and transpiration increased by 30-50% when considering the mulch layer. Annual total evaporation decreases by 4-10% according to mulch characteristics, leading to a better simulation of the annual and daily water balance of the sitz. A sensitivity analysis investigated the robustness of these results and possible causes of inaccuracies on half hour values. (C) 1999 Elsevier Science B.V. All rights reserved.