## Data and Methods
### LDAS-Monde System Components
#### 2.1.1 The SURFEX Modelling Platform  
LDAS-Monde uses the CO\({}_{2}\)-responsive version of ISBA embedded within the SURFEX platform. The most recent version of SURFEX (version 8.1) is used in this study with the \"NIT\" plant biomass monitoring option for ISBA. In this configuration, ISBA simulates leaf-scale physiological processes and plant growth [15; 16; 17]. The dynamic evolution of the vegetation biomass and LAI variables is driven by photosynthesis in response to atmospheric and climate conditions. Photosynthesis enables vegetation growth resulting from the CO\({}_{2}\) uptake. During the growing phase, enhanced photosynthesis corresponds to a CO\({}_{2}\) uptake, which results in vegetation growth from the LAI minimum threshold (prescribed as 1 m\({}^{2}\) m\({}^{-2}\) for coniferous forest or 0.3 m\({}^{2}\) m\({}^{-2}\) for other vegetation types). Transfers of water and heat through the soil rely on a multilayer diffusion scheme [29; 30]. The ISBA parameters are defined for 12 generic land surface patches. They include nine plant functional types (needle leaf trees, evergreen broadleaf trees, deciduous broadleaf trees, C3 crops, C4 crops, C4 irrigated crops, herbaceous, tropical herbaceous, and wetlands) as well as bare soil, rocks, and permanent snow and ice surfaces.  
This version of ISBA is coupled to the CTRIP river routing model through OASIS-MCT [31] in order to simulate streamflows of the main rivers [32; 33; 34; 35]. Besides, a single-source energy budget of a  
Figure 1: Averaged (**a**) surface soil moisture from the Climate Change Initiative project of ESA (for pixels with less than 15% of urban areas and with an elevation of less than 1500 m above sea level); (**b**) GEOV1 leaf area index from the Copernicus Global Land Service project (for pixels covered by more than 90% of vegetation) from 2010 to 2016. ESA CCI SSM—European Space Agency and Climate Change Initiative surface soil moisture; LAI—leaf area index.  
soil/vegetation composite is computed. SURFEX also involves data assimilation techniques to analyse LSVs from the ISBA LSM.  
This study makes use of the simplified version of an extended Kalman filter (SEKF), as already used and described in [13; 19; 21; 36]. The SEKF uses finite differences from perturbed simulations to estimate the linear tangent model linking the model state control variables to the observed variables. Satellite derived surface soil moisture (SSM) and leaf area index (LAI) are simultaneously assimilated to update eight model state control variables (i.e., control variables); LAI and soil moisture from seven layers of soil, from 1 cm to 100 cm. Assimilating SSM and LAI within LDAS-Monde results in updates of the LSM variables in different ways. Model variables corresponding to the observations are first updated through the Kalman gain computed by the SEKF. Secondly, control variables are updated through their sensitivity to the observed variables. For example, the assimilation of LAI impacts LAI itself, but also soil moisture from the seven layers present in the state vector and the assimilation of SSM impacts LAI. Finally, other variables are indirectly modified by the analysis through biophysical processes and feedbacks in the model by updates of the control variables.