## 2 Materials and Methods
### Reanalysis Data  
Meteorological reanalysis data provide an accurate description of the past weather by assimilating land surface and atmospheric observations from several sources into the most advanced numerical weather prediction models that obey physical laws, in order to create a complete and consistent climate dataset that covers several decades back in time and that is coherent both from physical and dynamic perspectives [53]. Reanalysis data are generally freely available on dedicated platforms of the web, released in regular grid formats, with a delay of few months from present. In this study, we employed the most advanced reanalysis data produced in Europe, specifically optimized for the land surface: UERRA MESCAN-SURFEX (UMS) [54] and ERA5-Land (E5L) [50, 55]. The former is a regional reanalysis model implemented for Europe within an European FP7 reanalysis preoperational project with the participation of the European Centre for Medium-Range Weather Forecasts (ECMWF), while the latter is a global atmospheric reanalysis model implemented by ECMWF. Both are freely available as products of the Copernicus Climate Change Service that holds the intellectual property rights of the raw data. UERRA MESCAN-SURFEX is a downscaled surface analysis system of the UERRA-HARMONIE regional reanalysis forced by the global ERA-Interim reanalysis data [56] and its production ceased with the end of availability of ERA-interim (July 2019). It will be replaced by a new system called Copernicus European Regional ReAnalysis (CERRA). CERRA will be used to create a pan-European reanalysis, with very high resolution (5.5 km) forced by the global ERA5 reanalysis [57]. UERRA MESCAN-SURFEX has a spatial resolution of 5.5 km over Europe and covers the period January 1961-July 2019. Figure 2a shows its numerical grid over the study area. Daily mean values of air temperature at 2 m, wind speed at 10 m, relative humidity at 2 m, global incoming solar radiation and barometric pressure as well as maximum and minimum daily air temperature were computed by aggregating the six-hour forecasts available at 00, 06, 12 and 18 UTC. ERA5-Land is a rerun of the land component of the ERA5 reanalysis, obtained by implementing a series of improvements with respect to ERA5, in order to make it more accurate for all types of land applications [58]. ERA5-Land runs at enhanced spatial resolution (9 km vs 31 km in ERA5), but it has the inconvenient that data, including atmospheric variables, are not provided for numerical grid points falling on sea surface. Thus, for land areas close to the coast, since they are not surrounded by four valid grid data values, the assessment of weather variables must rely on inland data only. Figure 2b shows the numerical grid of the E5L data: the gray dots refer to the grid points on the sea surface for which no data are available. Figure 2: Ground weather station sites (red triangles) and reanalysis grid points (**a**) UERRA MESCAN-SURFEX (UMS), blue circles; (**b**) ERA5-Land (E5L), green and gray circles. The gray circles are grid points located on the sea, for which E5L does not release data, being the reanalysis focused for the grid points located on the land. ERA5-Land data are produced with an hourly time-step. Thus, daily values were derived by collecting 24 values starting from 00 UTC every day. The available weather variables are air temperature at 2 m, wind speed at 10 m, global incoming solar radiation, barometric pressure and dew point temperature at 2 m. Instead of relative humidity, dew point temperature was then used for computing vapor pressure deficit. For both E5L and UMS data, a simple bias correction technique was applied to temperature, vapor pressure deficit and solar radiation data to remove the systematic bias. Raw reanalysis data were corrected by subtracting the corresponding regional mean bias computed at the 18 AWSs.