Impact of Leaf Area Index seasonality on the annual land surface evaporation in a global circulation model

Numerical experiments with the global model of the European Centre for Medium-Range Weather Forecasts (ECMWF) were devoted to the sensitivity of the modelled evaporation and precipitation to the vegetation Leaf Area Index (LAI). The temporally static LAI-distribution was replaced with a seasonally varying LAI, derived from Normalized Difference Vegetation Index (NDVI) archives. The seasonality of surface evaporation increased likewise, in combination with a response of increased precipitation seasonality over land. In a second set of experiments, the LAI-estimates were perturbed by a noise term reflecting measurement accuracy and interannual variability. The resulting noise in evaporation and precipitation was compared to the noise intrinsically generated by the atmosphere. For periods and areas where evaporation forms a large term in the surface energy balance, the noise added to the LAI could be clearly discerned from the atmospheric noise, indicating that improved LAIestimation techniques can have a detectable impact on the surface evaporation calculated in the ECMWF global model.