Assessing the Diurnal Cycle of Surface Energy and Water Fluxes in an Irrigated Agricultural field using an Hydrological Model

The diurnal variation of water and energy fluxes at the land surface is important to understand the diurnal cycle of photosynthesis, moisture and temperature at surface and deeper soil layers, especially during the growing season. The objective of the paper is to characterize the diurnal cycle of surface water and energy fluxes during the growing season of a corn in an irrigated agricultural field. The paper aims to study the response of the landsurface to observed atmospheric forcing at Citra, Florida, using a 1D column implementation of an existing land surface hydrology model. The observational data are analyzed first, including a careful analysis of physical consistency and measurement error. Particular emphasis is placed on the steps taken to evaluate and improve the quality of the two key physical forcing for the model: observed precipitation and radiation forcing. Simulations of energy fluxes, soil moisture and soil temperature from the model are compared against observations at fifteen minute time scales. The model is able to reproduce diurnal variability of the soil moisture and temperature in response to applied forcing. Root mean square error for soil moisture is calculated to be 0.033 m^3/m^3, 0.04 m^3/m^3, and 0.005 m^3/m^3 for superficial, middle and deeper layers respectively. A sensitivity study is conducted to investigate model behavior by changing thermal diffusivity and hydraulic diffusivity (not specified in the observation data), while keeping all other boundary conditions and physical forcing constant in the model. As opposed to previous applications with the model (at larger field scales and not for agricultural fields), it was found that thermal diffusivity and hydraulic diffusivity have a strong impact on the partitioning of the surface energy fluxes, especially in the case of thermal diffusivity with regard to diurnal variation of deep soil temperature.