# Monitoring and Forecasting the Impact of the 2018 Summer Heatwave on Vegetation
## 3 Results and Discussions
### Monitoring the Heatwave Impact on Vegetation Lising LDAS-Monde
From Figure 5 (all panels), one may see that LDAS-ERA5 and LDAS-HRES open-loops are quite comparable, LDAS-HRES open-loop being slightly better than LDAS-ERA5 open-loop in representing both LAI and soil moisture. It is also visible that the analyses add skill to both open-loops for both variables, which indicates the healthy behavior from the land data assimilation system. Over the whole common period (from April 2016 to October 2018), averaged R and RMSD values for LDAS-ERA5 open-loop (analysis) are 0.575(0.798) and 1.215 m\({}^{2}\)m\({}^{-2}\) (0.796 m\({}^{2}\)m\({}^{2}\)) for LAI, 0.748(0.772) and 0.038 m\({}^{3}\)m\({}^{-3}\) (0.035 m\({}^{3}\)m\({}^{-3}\)) for soil moisture, respectively. For LDAS-HRES, they are 0.601(0.808) and 1.150 m\({}^{2}\)m\({}^{-2}\) (0.772 m\({}^{2}\)m\({}^{-2}\)) for LAI and 0.750(0.772) and 0.038 m\({}^{3}\)m\({}^{-3}\) (0.036 m\({}^{3}\)m\({}^{-3}\)), respectively. It is also worth mentioning that if the analysis brings a clear improvement in the representation of LAI, reducing the overestimation in the senescence phase, as its model counterpart, it fails capturing the observed LAI onset. [PERSON] et al. [7] has evaluated the model sensitivity of the observation for Europe over 2000-2012 reflected in the SEKF Jacobians. The Jacobians depend on the  
Figure 4: **(a)** Observed CGLS GEOV2 Leaf Area Index (LAI) (green stars) over January 2008 to December 2018 as well as LDAS-Monde LAI time-series forced by either ERA5 (Open-loop is in blue, analysis is in red) over January 2008–October 2018 or high resolution operational analysis (HRES) (Open-loop is in cyan, analysis is in orange) over April 2016–December 2018. (**b**) Same as a) over Land Data Assimilation System (LDAS)-HRES and LDAS-ERA5 common period (April 2016 to October 2018). Data are averaged over the domain illustrated by Figure 2, dashed line represents the date from when HRES is available (April 2016) and the date up to when ERA5 is available (at the time of the study). model physics and their examination provides useful insight that explains the data assimilation system performances [34; 65]. [PERSON] et al. [7] suggests a seasonal dependency of the model sensitivity to the observed LAI. High sensitivity is found in autumn. Smaller model sensitivity at the time of the year where the LAI onset occurs (spring) prevails the analysis to match the observations correctly. As highlighted by [75], who have evaluated the capacity of several LSMs (including ISBA) to accurately simulate observed energy and water fluxes during droughs, there is a need to re-examine existing model components in LSMs to improve simulations of soil hydrological processes and water-plant interactions. Finally, Figure 6 shows LAI for the month of July 2018 from the open-loop, observations, analysis as well as LAI differences (analysis minus open-loop) for LDAS-ERA5 (upper panels, 0.25\({}^{\circ}\)\(\times\) 0.25\({}^{\circ}\) spatial resolution) and LDAS-HRES (lower panels, 0.10\({}^{\circ}\)\(\times\) 0.10\({}^{\circ}\) spatial resolution). From the two open-loops, one can see that LDAS-ERA5 and LDAS-HRES overestimate LAI with respect to the observations. LDAS-HRES open-loop is however in better agreement with the observations than LDAS-ERA5 open-loop, particularly over the area most affected by the heatwave (e.g., over Belgium, the Netherlands, Germany and Poland). While the assimilation is efficiently reducing LAI in both LDAS-ERA5 and LDAS-HRES analyses, the latter is in better agreement with the observations than LDAS-ERA5 analysis. Despite their spatial resolution differences, ERA-5 and HRES results present  
Figure 5: Upper panel, seasonal (**a**) root mean square differences (RMSD) and (**b**) correlation values between leaf area index (LAI) from the model forced by either ERA5 (LDAS-ERA5 Open-loop in blue) or HRES (LDAS-HRES Open-loop in cyan), the analysis forced by either ERA5 (LDAS-ERA5 Analysis in red) or HRES (LDAS-HRES Open-loop in pink) and GEOV2 LAI estimates from the Copernicus Global Land Service project from April 2016 to October 2018.