Bulk Canopy Conductance and NDVI Along a Precipitation Gradient During IHOP 2002 in the U.S. Southern Great Plains

Bulk canopy conductance (Gc) of water was calculated from a rearranged form of the Penman-Monteith equation for nine surface flux stations across a precipitation gradient for different land-uses during the International H2O Project 2002 in the U.S. Southern Great Plains. Gc is compared to ground-based normalized difference vegetation index (NDVI) measurements from mid-May through late July 2002. The putative relationship of which - under optimal environmental conditions of high vapor pressure deficit (D), photosynthetic photon flux density (PPFD), and soil moisture (Theta) - may provide an upper bounds for Gc (Gcmax). Here we explore the relationship of Gcmax as a function of NDVI for optimal D, PPFD and Theta as well as the influence of suboptimal D, PPFD and Theta on this relationship to constrain Gcmax to Gc. The potential for separating Gc into its primary components of soil conductance (Gg) and stomatal conductance (Gs) is also examined using a log-linear model to calculate Gs, leaving the residual Gg. This could be useful in estimating Gc, which may allow subsequent separation of the relative contribution of Gg and Gs to Gc using the log-linear relationship of Gs to D in addition to constraints of PPFD and Theta on Gs. Such an approach could be especially powerful when combining satellite NDVI with remotely sensed soil moisture indices to generate these relationships.