# Monitoring and Forecasting the Impact of the 2018 Summer Heatwave on Vegetation
## 2 Material and Methods
### LDAS-Monde  
Within the SURFX modeling platform of Meteo-France (Surface Externalisee, [50], Version 8.1), the LDAS [32; 33; 34; 39; 51] developed in the research department of Meteo-France, the CNRM (Centre National de Recherches Meteorologiques) permits integrating satellite products into the ISBA (Interaction between Soil Biosphere and Atmosphere) LSM [52; 53; 54; 55] using a data assimilation scheme. The LDAS was extended to a global scale (LDAS-Monde, [18]). At the same time, the coupling to hydrological models (ISBA-CTRIP for ISBA-CNRM, Total Runoff Integrating Pathways) was consolidated. A full description of the ISBA-CTRIP system is presented in [56]. The obtained land surface reanalyses from LDAS-Monde account for the synergies of various upstream products (e.g., model and satellite derived observations) and are able to provide an improved representation of LSVs, as well as statistics which can be used to monitor the quality of the assimilated observations (e.g., [7; 18; 35]). LDAS-Monde can also be used to calibrate model parameters (e.g., [57] for the soil maximum available water content within ISBA). LDAS-Monde uses the CO\({}_{2}\)-responsive [53; 54; 55], multi-layer soil [56; 57; 58; 59], version of ISBA. The latter allows to solve the energy and water budgets at the surface level and describes the exchanges between the land surface and the atmosphere. Parameters in ISBA are defined for 12 generic land surface patches: nine plant functional types (namely: needle leaf trees, evergreen broadleaf trees, deciduous broadleaf trees, C3 crops, C4 crops, C4 irrigated crops, herbaceous, tropical herbaceous, and wetlands, C3 and C4 refer to different processes that plants use to fix carbon during the process of photosynthesis) as well as bare soil, rocks, and permanent snow and ice surfaces. They are derived from ECOCLIMAP-II, the land cover map used in SURFEX [60]. Atmospheric and climate conditions drive the dynamic evolution of the vegetation biomass and LAI through vegetation growth and mortality processes implemented in the form of a nitrogen dilution process (NIT option) [53; 55; 61]. Photosynthesis enables vegetation growth resulting from the CO2 net assimilation. During the growing phase, enhanced photosynthesis corresponds to a CO2 net assimilation, which results in vegetation growth from the LAI minimum threshold (1 m\({}^{2}\)m\({}^{-2}\) for coniferous forest or 0.3 m\({}^{2}\)m\({}^{-2}\) for other vegetation types). Vegetation phenology relies on photosynthesis-driven plant growth and mortality, and photosynthesis is related to the mesophyll conductance. More information on the CO\({}_{2}\)-responsive version of ISBA can be found in [62; 63] and by visiting the SURFEX website (www.umr-cnrm.fr/surfex, last access: February 2019). The multilayer diffusion scheme described in [58; 59] drives transfers of water and heat through the soil. Finally, the Simplified Extended Kalman Filter Data Assimilation (DA) technique (SEKF, [32; 33; 34; 39; 51]) is the main technique available within LDAS-Monde. While ensemble based DA techniques are currently being tested and implemented [39; 64], to date the LDAS-Monde SEKF is the most robust. It uses finite differences to compute the flow dependency between the assimilated observations (SSM and LAI) and the analyzed variables (soil moisture from soil layer 2 (1 cm to 4 cm) to layer 8 (80 cm to 100 cm), representing the first meter of soil and LAI, see Table 1). Further details of the analysis methodology can be found in [18; 34]. While control variables are directly updated through their sensitivity to the observed variables, expressed by the SEKF Jacobians [18; 65], other variables are indirectly modified by the analysis through biophysical processes and feedback in the model by updates of the control variables.