Improving the simulation of the leaf-to-canopy scaling of solar-induced chlorophyll fluorescence in Community Land Model version 5

Abstract:

Incorporation of the simulation of solar-induced chlorophyll fluorescence (SIF) in Land Surface Models (LSMs) is a prerequisite for validating and constraining the simulation of terrestrial gross primary productivity (GPP) in LSMs with SIF observations. Recently, SIF simulations have been incorporated into a few LSMs, but the scaling of SIF from leaf-level to canopy-level is usually not well-represented. We incorporate the simulation of SIF into the Community Land Model version 5 (CLM5). An efficient method is proposed to scale SIF from leaf-level to canopy-level while taking clumping, canopy scattering, and viewing geometry into account. Model simulated SIF generally captures the magnitude and spatiotemporal pattern of satellite observed SIF (R² = 0.85), while discrepancies are found for some biomes. In temperate forests, CLM SIF agrees well with SIF observed by the Global Ozone Monitoring Instrument version 2 (relative error generally less than 10%). But CLM tends to overestimate SIF in boreal and tropical regions (by roughly 50% and 30%, respectively) and underestimate SIF in croplands (by around 30%). Incorporation of canopy clumping and viewing geometry reduces simulated nadir SIF by around 8% and 26 %, respectively. By providing a more mechanistic method for simulating sensor-observed SIF in LSMs, our work may facilitate the use of SIF observations for validating and constraining GPP modeling.