What is the best way to represent surface conductance for a range of vegetated sites?

Surface conductance G s is a significant parameter for indicating the evaporative and photosynthetic properties of a vegetated surface. When comparing G s values between different observation sites, some studies have used G smax and others have used Ĝ smax (where G smax is the maximum G s value measured during the measurement period, and Ĝ smax is the maximum G s value obtained with a vapour pressure deficit (VPD) of ≥ 1·0 kPa during the measurement period). In this study, we demonstrate a clear justification for using Ĝ smax instead of G smax when comparing G s values between different sites. We examined whether both Ĝ smax and G smax lead to the same conclusions in classifying vegetated sites. Komatsu (2003b) [ Hydrological Processes 17: 2503–2512] reported a clear relationship between canopy height h and Ĝ smax for coniferous forests with a projected leaf area index (LAI) of ≥ 3·0. We examined not only the relationship between h and Ĝ smax but also the relationship between h and G smax for coniferous forests with a projected LAI of ≥ 3·0. Both Ĝ smax and G smax decreased with increasing h . However, the relationship between h and G smax was less well defined than the relationship between h and Ĝ smax because of biased G smax data. Consequently, we conclude that Ĝ smax is a more appropriate index than G smax to represent G s for sites with different vegetation. Copyright © 2007 John Wiley & Sons, Ltd.