Energy and Water Balance of An Irrigated Agricultural Area in Northern Utah.

Traditionally, the components of the water balance such as evapotranspiration are approximated with a conservation of mass approach requiring detailed flow measurements. Hydrological models for a region can estimate the quantity of the different water balance components including evapotranspiration. At present, the use of remote sensing techniques provided the application of surface energy balance methods for accurate calculations of evapotranspiration at a regional scale. Models exist for estimating the latent heat flux, which represents the energy component for evapotranspiration. These two distinct methods are compared in this presentation using data from a 26800 ha irrigated agricultural system in Northern Utah. The farmers in this agricultural region mainly practice surface irrigation to water their grain and forage crops.

Flow measurements through-out the irrigation system provides the data necessary to evaluate the input of irrigation water to the farm fields. Additionally, on-farm irrigation evaluations are performed for different soils to determine the infiltration. Using an appropriate hydrological model, the water balance found at the field level can be expanded to a regional level, using spatial GIS datasets for soil types. These values are compared with the crop evapotranspiration estimated with a surface energy balance model SEBAL, applied using satellite and airborne shortwave and thermal infrared imagery. This model has been used in various countries and is proven to be applicable for macro-scale evapotranspiration estimates. The model is run for a number of remote sensing images throughout the irrigation season and validated with ground-data.

Results from both the water and surface energy balance methods are compared for the same irrigation season. Outputs indicate the degree of cohesiveness between the two methods in estimating evapotranspiration at an irrigation system scale and gives insight in the applicability of both techniques.