An alternative approach to determining zero-plane displacement, and its application to a lotus paddy field

We propose an alternative approach to determining zero-plane displacement by using friction velocities obtained by measuring wind profile and eddy correlation. In this approach, zero-plane displacement is determined so that the slope of the regression line between the friction velocities obtained from the wind profile and eddy correlation is close to 1. The approach was applied to a lotus paddy field in the back marsh of Lake Kasumigaura, Japan, and yielded acceptable results. The values determined for the normalized displacement height (0.13–0.91) and the normalized roughness length (0.023–0.092) of the lotus canopy were close to those of hard-canopy stands, such as forests and cornfields. These results are attributed to the unique structure of the lotus canopy (large, round leaves on the top of hard, thick shoots). In addition, the normalized displacement height of the lotus canopy increased linearly with the leaf area index (LAI). Because the number of comprehensive observation sites for flux measurements and micrometeorology has increased in recent years, this approach could be applicable to other study sites where there are problems in determining zero-plane displacement by the conventional method, which uses wind profile data alone.