Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Determination of regional scale crop coefficients for crop water requirement calculations a RS perspective (Kenya)

Auteur : Mekonnen, Woldemariam

Etablissement de soutenance : International Institute for Aerospace Survey, Netherlands

Grade : Master of Science (MSc) 1999

Résumé
Since the publication of FAO booklets in the late seventies (Doorenbos and Pruitt, 1977), the calculation of crop potential evapotranspiration (ETc) through a combination of reference evapotranspiration (ETref) with appropriate crop coefficients (Kc) has become increasingly popular among practicing irrigation engineers and water managers. This study investigates the application of satellite data to obtain regional scale Kc analytically without the prior knowledge of crop type and stage of growth. During approximately 10 days, a field campaign was held in the Lake Naivasha Vineyard Farm, Kenya to collect data on surface energy variables. Using the relevant field data, ETc values have been calculated using an energy balance residual- and Priestley Taylor equations in Squash, Bean, and Chilli fields. The latter equation, with the Priestley-Taylor ? parameter = 1.26, has yielded ETc values that are compatible with those obtained using the former equation. An empirical equation has also been developed to calculate ETc using only incoming solar radiation and surface temperature data. ETref can be calculated using the same Priestley-Taylor equation, with surface albedo = 0.23. By taking the quotient between Priestley-Taylor equations for ETc and ETref, the formulation for Kc is stated, both on instantaneous and daily temporal scales. Attempts are also made to further simplify Kc input parameters. Kc values calculated using the Kc equation are compared to those derived from the FAO Table. The Kc equations are then applied to satellite data. The resulting Kc and ETc maps, based on the LANDSAT-TM data, are displayed. For small scale irrigated areas, like that of the study area, the spatial resolution of NOAA-AVHRR imagery is found to be unsuitable for the calculation of Kc using the derived equations. However, the procedure which ought to be followed while applying the derived Kc equations to NOAA-AVHRR data acquired over large-scale irrigated areas is outlined.

Sujets : Lake Naivasha, Kenya ; Hydrology ; Meteorology ; Water ; Irrigation ; Remote sensing ;

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