In this paper, we investigate the statistical features of the influences of local zero-plane displacement on effective roughness length and effective zero-plane displacement for three surface categories, with a so-called joint calculation scheme for effective aerodynamic parameters over heterogeneous terrain proposed by Zhong et al. [Zhong Z, Lu W, Song S and Zhang Y 2011 J. Hydrometeor. 12 1610]. The local zero-plane displacement is found to magnify the effective roughness length. However, such a magnification effect tends to decrease as the roughness step increases. On the other hand, the effective zero-plane displacement increases as local zero-plane displacement increasing, though it is always less than the area-weighted linear average of the local zero-plane displacement. However, the effective zero-plane displacement tends to decrease with the roughness step increasing.