This study evaluated the effect of soil surface moisture on the performance of the original and modified Penman method by two-wind function. The evapotranspiration was obtained with constant water table lysimeters. In Period I, the border area of lysimeter was wetted by precipitation only and due to water table depth (46 cm) the soil surface remained dry. A plastic cover was placed on the lysimeters during the rainy days. During the Period II, the border area of lysimeter was irrigated and water table depth at 30 cm allowed soil surface to be maintained wet. In Period I, the Penman method overestimated evapotranspiration and the obtained wind function showed to be physically inconsistent. In Period II, the original and modified Penman methods showed better performance demonstrating the importance of maintaining moisture content of soil surface constant.
available water; lysimeters; evapotranspiration
