Combining a large aperture scintillometer and estimates of available energy to derive evapotranspiration over several agricultural fields in a semi-arid region

Abstract

The objective of the present study was to investigate the potential of a large aperture scintillometer (LAS) combined with a simple available energy model to estimate area-averaged latent heat flux in difficult environmental conditions. The difficulties are related to the sparseness of the vegetation, the heterogeneity of the soil characteristics, and, most importantly, the heterogeneity in terms of soil moisture induced by the “flood irrigation” method. In this context, three sites (Agdal, R3 and Sâada) in the Tensift Al Haouz plain (region of Marrakech city, central Morocco) have been equipped with a LAS and eddy covariance (EC) system (local scale measurements). Agdal and R3 are a flood-irrigated olive yard and wheat field, respectively. Sâada is a drip-irrigated orange orchard. Due to the irrigation method applied, the Agdal and R3 sites shifted from being almost homogeneous between two irrigations (dry conditions) and completely heterogeneous during the irrigation events (large variability of soil moisture along the site), while Sâada was always heterogeneous, at least at the scintillometer footprint scale. Consequently, the comparison between the sensible heat fluxes derived from both LAS and EC showed a large scatter during the irrigation events, while a good correspondence was found in between two irrigations. It was also found that combining LAS and an estimate of the available energy (using a simple model) can provide reasonable large-scale evapotransipration estimates, which are of prime interest for irrigation management.

Keywords:

• Evapotranspiration
• olive
• orange
• scintillation
• semi-arid region
• wheat

Acknowledgements

This research was performed within the framework of SUDMED, EU-funded IRRIMED (http://www.irrimed.org), and PLEIADES (http://www.pleiades.es) projects. We are grateful to the Institut de Recherche pour le Développement (IRD, France) and to the director and staff of the Agdal olive and Sâada orange orchards, for access and use of the field site and for assistance with irrigation scheduling and security. We thank the CMIFM (Comité Mixte Inter-universitaire Franco-Marocain) committee for its financial support in the framework of a P.A.I. programme (2006–2009). The authors are grateful to ORMVAH (Office Regional de Mise en Valeur Agricole du Haouz, Marrakech, Morocco) for its technical help in the R3 wheat site.