Submitted to: Transactions of the ASABE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/15/2011
Publication Date: 9/30/2011
Citation: Licciardello, F., Rossi, C.G., Srinivasan, R., Zimbone, S.M., Barbagallo, S. 2011. Hydrologic evaluation of a Mediterranean watershed using the SWAT model with multiple PET estimation methods. Transactions of the ASABE. 54(5):1615:1625. Interpretive Summary: A semi-arid Mediterranean watershed has been evaluated using the Soil and Water Assessment Tool. Within this watershed in Sicily, water quantity is difficult to simulate due to climate variability and the impact of geological structures. Few hydrologic studies have been conducted in the Mediterranean however there is substantial interest to identify a prediction model that can provide realistic and adequate simulations to assist water resources management as directed by the United Nations and the European Union. A water quantity evaluation requires using a correct potential evapotranspiration (PET) method to describe the area being simulated. The recommended evapotranspiration procedure by the Food Agricultural Organization is the Penman-Monteith method stated in the Irrigation and drainage paper 56 (FAO-56 P-M). The three existing PET methods were compared to the FAO-56 P-M. The water balance was better predicted using the FAO-56 P-M method because the surface runoff was more realistic. The addition of this method broadens the model’s capability to be applicable to semi-arid environments with high intensity, short duration rainfall events.
Technical Abstract: The Penman-Monteith method suggested by the Food Agricultural Organization in the Irrigation and drainage paper 56 (FAO-56 P-M) was used to evaluate surface runoff and sediment yield predictions by the Soil and Water Assessment Tool (SWAT) model at the outlet of an experimental watershed in Sicily. A sensitivity analysis determined the potential evapotranspiration (PET) parameter as the most sensitive out of 10 parameters impacting surface runoff and sediment volumes in this small Mediterranean watershed. The FAO-56 P-M method was employed in the SWAT model to determine the model’s ability to adequately simulate the water balance within this region from 1997 to 2003 compared with the three PET methods previously existing in SWAT. The water balance was more realistically reflected by the FAO-56 P-M method than by the other PET methods in this watershed. The traditional P-M method incorporated into SWAT overestimated total (surface and base flow) runoff volumes observed during the entire period by approximately 50 percent; total runoff volumes were underestimated by only 17 percent when the FAO-56 P-M method was used. The surface runoff simulation results using the FAO-56 P-M potential evapotranspiration (PET) equation for calculating daily values was good at monthly and event scale (E> 0.75) during both the calibration and validation periods. The simulation of 25 observed sediment yield events was good (E=0.91) and satisfactory (E=0.44) during the calibration and validation period respectively, after adjusting the USLE_C parameter by approximately 90 percent of the original default value. The incorporation of the FAO-56 P-M method has broadened the model’s applicability to watershed’s that are in semi-arid environments with high intensity, short duration rainfall events.