European Field Experiment Research Articles

Parameterisations for energy transfers from a sparse vine crop

Parameterisations are presented for the energy budget of a sparse vine crop growing under semi-arid conditions in southern Spain. The measurements were made as part of the European Field Experiment in a Desertification-threatened Area (EFEDA) project which has as one of its main aims the development of regional scale land-atmosphere models appropriate to sparse crops and natural vegetation growing under these conditions. The results presented here should prove useful to this objective as well as providing information of more general interest for modelling sparse crops. All of the main components in the energy balance were recorded, including the sensible and latent heat fluxes which were measured using eddy correlation equipment. The measurements were made over the first 50 days of plant growth during which the plant area coverage increased from zero to about 30%. Over this period, 18 mm of rainfall was recorded and the maximum soil moisture content reached was about 5% in the 0–5cm surface layer. The measurements have been interpreted within the framework of the Shuttleworth—Wallace energy combination model. The roughness length increased from about 0.01 m to 0.04–0.06 m for the fully grown vines and peak daily bulk canopy conductances increased from about 0.5 mm s −1 to 1.5 mm s −1. Results are also presented for the influence of plant growth and variations in soil moisture on the overall available energy and the energy partition between the plants and bare soil. The models suggest that, of the total observed evaporation of 69 mm, approximately 45 mm could be attributed to plant transpiration with the remainder arising from the bare soil.