Estimation of the minimum canopy resistance for croplands and grasslands using data from the 2002 International H₂0 Project

The mean rcmin for all the sites is 72 s m⁻¹ with a standard deviation of 39 s m⁻¹. This variability is due to both the empirical nature of the Jarvis scheme and a combination of changing environmental conditions, such as plant physiology and plant species composition, that are not explicitly considered by the scheme. This variability in rcmin has important implications for land surface modeling where rcmin is often parameterized as a constant.

For example, the Noah land surface model parameterizes rcmin for the grasslands and croplands types in this study as 40 s m⁻¹. Tests with the coupled Weather Research and Forecasting (WRF)-Noah model indicate that the using the modified values of rcmin from this study improves the estimates of latent heat flux; the difference between the observed and modeled moisture flux decreased by 50% or more. While land surface models that estimate transpiration using Jarvis-type relationships may be improved by revising the rcmin values for grasslands and croplands, updating the rcmin will not fully account for the variability in rcmin observed in this study.

As such, it may be necessary to replace the Jarvis scheme currently used in many land surface and numerical weather prediction models with a physiologically based estimate of the canopy resistance.