Estimation of zero-plane displacement height and aerodynamic roughness length on rice fields

The estimation of aerodynamic roughness length (z0) and zero-plane displacement height (d) is of primary importance in the application of a number of models that simulate soil-vegetation-atmosphere interactions at different spatial scales. Many efforts to directly measure z0 and d in the case of various surfaces were conducted in the past from multi-level measurements of wind speed over homogeneous surfaces, but results reported in the literature are still rare for some canopies and can only be used as a rule of thumb. In this work, values of d and z0 along the whole agricultural season for two rice fields located in northern Italy and characterized by different irrigation managements (continuous flooding and intermittent irrigation) were obtained from single level turbulence measurements performed by an eddy covariance (EC) system installed on the levee between the two fields. Throughout the growing season, d and z0 appeared to be well correlated (R2 greater than 90%) with the vegetation height (hv) and the mean value of the ratio between d and hv was about 0.75 for both rice fields, while the ratio between z0 and hv was about 0.06 and 0.05 respectively for the flooded and the intermittent irrigation treatments. Moreover, d and z0 did not show any clear dependence on wind speed or stability conditions of the atmosphere. Keywords: aerodynamic roughness length, zero-plane displacement height, eddy covariance, paddy field, aerobic rice, northern Italy.