Global variability of simulated and observed vegetation growing season

Vegetation phenology and its variability have substantial influence on land-atmosphere interaction, and changes in growing season length are additional indicators of climate change impacts on ecosystems. For these reasons, global land surface models are routinely evaluated in order to assess their ability to reproduce the observed phenological variabil- ity. In this work, we present a new approach that integrates a wider spectrum of growing season modes, in order to better describe the observed variability in vegetation growing season onset and offset, as well as assess the ability of state-of-the-art land surface mod- els to capture this variability at the global scale. The method is applied to the Community Land Model version 4.5 (CLM4.5) simulations and LAI3g satellite-observation. The com- parison between data and model outputs shows that CLM4.5 is capable of reproducing the growing season features in the Northern Hemisphere mid- and high-latitudes, but also displays its limitations in areas where water availability acts as the main driver of veg- etation phenological activity. Besides, the new approach allows evaluating land surface models in capturing multi-growing-season phenology. In this regard, CLM4.5 proves its ability in reproducing the two-growing-season cycles in the Horn of Africa. In general, the new methodology expands the area of analysis from northern mid- and high-latitudes to the global continental areas, and allows to assess the vegetation response to the ongoing climate change in a larger variety of ecosystems, ranging from semi-arid regions to rain forests, passing through temperate deciduous and boreal evergreen forests.