Abstract
A surface energy balance model was conceived to estimate crop transpiration and soil evaporation in orchards and vineyards where the floor is partially wetted by micro-irrigation systems. The proposed surface energy balance model for partial wetting (SEB-PW) builds upon previous multiple-layer modelling approaches to estimate the latent, sensible, and soil heat fluxes, while partitioning the total evapotranspiration ( E T ) into dry and wet soil evaporation ( λ E s o i l ) and crop transpiration ( T ). The model estimates the energy balance and flux resistances for the evaporation from dry and wet soil areas below the canopy, evaporation from dry and wet soil areas between plant rows, crop transpiration, and total crop E T . This article describes the model development, sensitivity analysis and a preliminary model evaluation. The evaluation shows that simulated hourly E T values have a good correlation with field measurements conducted with the surface renewal method and micro-lysimeter measurements in a micro-irrigated winegrape vineyard of Northern California for a range of fractional crop canopy cover conditions. Evaluation showed that hourly L E estimates had root mean square error ( R M S E ) of 58.6 W m−2, mean absolute error ( M A E ) of 35.6 W m−2, Nash-Sutcliffe coefficient ( C N S ) of 0.85, and index of agreement ( d a ) of 0.94. Daily soil evaporation ( E s ) estimations had R M S E of 0.30 mm d−1, M A E of 0.24 mm d−1, C N S of 0.87, and d a of 0.94. E s estimation had a coefficient of determination ( r 2 ) of 0.95, when compared with the micro-lysimeter measurements, which showed that E s can reach values from 28% to 46% of the total E T after an irrigation event. The proposed SEB-PW model can be used to estimate the effect and significance of soil evaporation from wet and dry soil areas on the total E T , and to inform water balance studies for optimizing irrigation management. Further evaluation is needed to test the model in other partially wetted orchards and to test the model performance during all growing seasons and for different environmental conditions.
Highlights
Evapotranspiration (ET) is generally the second largest component of water balance, following precipitation
This study indicated that the two-layer model overestimated the latent heat flux and ET by about 2% and 6%, respectively, and that the model was very sensitive to errors in the measurements of stomatal conductance
Similar to previous multiple-layer model approaches [25,26], the modified surface energy balance model for partial wetting (SEB-PW) model has four layers (Figure 1): The first layer extends from the reference height above the vegetation to the sink for momentum within the canopy; a second layer spans between the canopy and the soil surface, followed by a third layer comprising the top soil layer, where the surface resistance can be calculated as a function of the soil water content
Summary
Evapotranspiration (ET) is generally the second largest component of water balance, following precipitation. Researches and water resource managers require accurate and reliable ET estimates to understand water availability and distribution for both short and long-term water resource. Water 2019, 11, 1747 management [1]. ET is the amount of water lost to the atmosphere, including net water evaporation and the water transferred through the vascular system of the plant into the atmosphere from leaves. Water managers and growers seek robust methods to quantify ET and assess the impact of water management and conservation measures, such as to reduced tillage, on ET during crop growing seasons [2]. Evapotranspiration is an integrated term, composed of the precipitation intercepted by plant canopies, vapor fluxes of plant transpiration, and soil evaporation [3]
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