Abstract
Abstract. Plant phenology plays a fundamental role in land–atmosphere interactions, and its variability and variations are an indicator of climate and environmental changes. For this reason, current land surface models include phenology parameterizations and related biophysical and biogeochemical processes. In this work, the climatology of the beginning and end of the growing season, simulated by the land component of seven state-of-the-art European Earth system models participating in the CMIP6, is evaluated globally against satellite observations. The assessment is performed using the vegetation metric leaf area index and a recently developed approach, named four growing season types. On average, the land surface models show a 0.6-month delay in the growing season start, while they are about 0.5 months earlier in the growing season end. The difference with observation tends to be higher in the Southern Hemisphere compared to the Northern Hemisphere. High agreement between land surface models and observations is exhibited in areas dominated by broadleaf deciduous trees, while high variability is noted in regions dominated by broadleaf deciduous shrubs. Generally, the timing of the growing season end is accurately simulated in about 25 % of global land grid points versus 16 % in the timing of growing season start. The refinement of phenology parameterization can lead to better representation of vegetation-related energy, water, and carbon cycles in land surface models, but plant phenology is also affected by plant physiology and soil hydrology processes. Consequently, phenology representation and, in general, vegetation modelling is a complex task, which still needs further improvement, evaluation, and multi-model comparison.
Highlights
We inspect the main differences between LAI3g, Moderate Resolution Imaging Spectroradiometer (MODIS), and CGLS by plotting the spatial distribution of the four growing season types, growing season start (GSS), and growing season end (GSE) (Fig. 2)
Compared to MODIS, LAI3g differs mainly in EVG regions (Table 2) due to an underestimation of EVG areas in the tropics (Fig. S2 in the Supplement). These regions are characterized by high canopy density, which saturates to high leaf area index (LAI) in the satellite data (e.g. Myneni et al, 2002), resulting in limited seasonal variability
This study evaluates the ability of the land component (LSMs) of seven state-of-the-art European Earth system models participating in the CMPI6 to reproduce the timings of the start and end of the plant growing season at the global level
Summary
Plant phenology and its variability have a substantial influence on the terrestrial ecosystem (e.g. Churkina et al, 2005; Kucharik et al, 2006; Berdanier and Klein, 2011) and land– atmosphere interactions (e.g. Cleland et al, 2007; Richardson et al, 2013; Keenan et al, 2014). The work by Richardson et al (2012) is an example of a systematic evaluation of LSMs’ phenology representation They evaluate 14 models participating in the North American Carbon Program Site Synthesis against 10 forested sites, within the AmeriFlux and FLUXNET Canada networks. Their assessment reveals a typical bias of about 2 weeks in LSM representation of the beginning and end of the growing season. The work by Buermann et al (2018) is another example of a multi-LSM evaluation They observe widespread lagged plant productivity responses across northern ecosystems associated with warmer and earlier springs, which is weakly captured by 10 evaluated TRENDYv6 current LSMs. current LSMs still present biases in simulating timings and the magnitude of the vegetation active season
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