Abstract
The value-added by plastic film mulches are numerous in agricultural productivity and its global acceptance is unprecedented. However, its disturbing effects on the natural water cycling, surface energy fluxes and partitioning of evapotranspiration (ET) in drip-irrigated fields with plastic film mulch are often overlooked or not investigated due to deficiencies in existing process-based ET models. This study optimized the simulation of plastic film-mulched soil effects on surface energy fluxes by incorporating a thermal contact resistance component into a satellite derived Land Surface Temperature-based Two-Source Energy Balance (i.e.,TSEBPM) model, in a drip-irrigated cotton field for two consecutive growing seasons (2009 and 2010). The optimized model agrees better with Eddy Covariance (EC) flux tower observation and showed reduced error biases than the original TSEB model. The RMSE values decreased for the net radiation, latent, sensible and ground heat fluxes by 10.85, 1.93, 4.84, 0. 81 (Wm−2), respectively. Moreover, ET partitioning by TSEBPM revealed the actual contribution of evaporation (E) and transpiration (T) in cotton water use at different growth stages. When cotton growth reaches the ball-opening stage (i.e., harvesting period or cotton canopy coverage > 75%), the mean E/ET value was 0.20 ± 0.05, while T/ET was 0.79 ± 0.05 during the irrigation seasons. Meanwhile, the plastic mulching altered the reflected shortwave radiation, thereby impacting on surface albedo reflectance under well saturated cotton canopy. As such, the transpiration sub-model parameters such as fractionalvegetationcover and vegetationgreenfraction had influential effects, and are the most sensitive in the TSEBPM model parameterization. This study showed that TSEBPM can provide robust insights into the effects of plastic mulching on surface energy fluxes and cotton ET, therefore can be explored further across arid agroecosystems.
