Sensitivity of Surface Fluxes in the ECMWF Land Surface Model to the Remotely Sensed Leaf Area Index and Root Distribution: Evaluation with Tower Flux Data

Abstract

The surface-atmosphere turbulent exchanges couple the water, energy and carbon budgets in the Earth system. The biosphere plays an important role in the evaporation process, and vegetation related parameters such as the leaf area index (LAI), vertical root distribution and stomatal resistance are poorly constrained due to sparse observations at the spatio-temporal scales at which land surface models (LSMs) operate. In this study, we use the Carbon Hydrology Tiled European Center for Medium-Range Weather Forecasts (ECMWF) Scheme for Surface Exchanges over Land (CHTESSEL) model and investigate the sensitivity of the simulated turbulent fluxes to these vegetation related parameters. Observed data from 17 FLUXNET towers were used to force and evaluate model simulations with different vegetation parameter configurations. The replacement of the current LAI climatology used by CHTESSEL, by a new high-resolution climatology, representative of the station’s location, has a small impact on the simulated fluxes. Instead, a revision of the root profile considering a uniform root distribution reduces the underestimation of evaporation during water stress conditions. Despite the limitations of using only one model and a limited number of stations, our results highlight the relevance of root distribution in controlling soil moisture stress, which is likely to be applicable to other LSMs.

Upgrading Land‐Cover and Vegetation Seasonality in the ECMWF Coupled System: Verification With FLUXNET Sites, METEOSAT Satellite Land Surface Temperatures, and ERA5 Atmospheric Reanalysis

“…In fact, the calibration of model parameters is paramount, as the current model configuration has been tuned based on an outdated land cover data set. As an example, Stevens et al (2020) investigated the close relationship between LAI and the minimum stomatal resistance and rooting depth in CHTESSEL showing some potential to improve the latent heat flux variability via an adjustment of these parameters. However, those results were based on offline simulations for 17 flux towers.…”

ERA5-Land: a state-of-the-art global reanalysis dataset for land applications

“…This may induce changes to traditional watering crop strategies, harvesting periods, pest management, or even crop culture replacements. Likewise, insurance (and reinsurance) companies need reliable historical data to assess the risk of severe droughts or flooding (Tadesse et al, 2015;Jensen and Barrett, 2016), in particular for smallholder agriculture. For public and private stakeholders, offline land surface datasets can provide complementary information needed to support decision makers.…”

ECLand: The ECMWF Land Surface Modelling System

“…This uniform distribution replaces the current exponential formulation and depends only on the maximum rooting depth (R DMAX ). This root distribution formulation was investigated by Stevens et al [48] and showed potential for improvement of the water and energy fluxes. The transformation of root zone soil moisture to water stress is also an open question, and there are different approaches to relate root zone soil moisture and the water stress factor [49,50].…”