A low complexity vegetation model to simulate Leaf Area Index and Gross Primary Productivity for use in hydrological models

Abstract:

The realistic representation of vegetation dynamics in environmental models has a substantial impact on simulated water and carbon fluxes. Hydrological models are often used to estimate and assess the impact of drought conditions across a variety of spatial and temporal scales. However, vegetation dynamics in hydrological models are often poorly represented, given the inherent complexity and associated challenges with carbon cycle representation. In this study we focus on capturing the seasonal dynamic of vegetation's leaf area index (LAI) and gross primary productivity (GPP). The former is a key determinant for evapotranspiration estimation in hydrological models and the latter is the largest CO₂ flux of the carbon cycle in terrestrial ecosystems representing the net atmosphere-land CO₂ flux. We developed a low complexity vegetation model based on the light use efficiency concept with a small number of parameters to simulate dynamics of leaf biomass (related to changes in LAI) and GPP. Our proposed model calculates daily leaf biomass from the difference between daily canopy carbon uptake and sinks that include leaf respiration and turnover. The model is solved with a finite difference approximation and consists of several sub-models including pedotransfer function, effective daily soil moisture weighted by vertical root distribution, phenology, and leaf litter generation. We establish the proposed vegetation model and analyze the sensitivity of different model parameterizations on the resulting carbon flux dynamics (GPP). Model performance is evaluated against in-situ measurements from a deciduous broadleaf forest site located in central Germany within TERENO data network. The model adequately captures the daily dynamics of observed GPP with R² > 0.88. In this presentation, we will present and discuss the suitability of the proposed vegetation model structure and the uncertainty in model parameterizations for simulations of carbon fluxes.