# Evaluation of Five Reanalysis Products over France: Implications for Agro-Climatic Studies
## 2 Materials and Methods
### Agro-Climate Indicators  
To represent the potential effects of weather conditions on crop productivity and management, a set of six AgcIs were chosen based on the two common climate variables among the datasets: daily mean temperature and daily total precipitation. The AgcIs, summarized in Table 2, were selected to cover various aspects of climate impact on agriculture. The concept of growing degree days (GDD) is first introduced before briefly describing the AgcIs below. GDD measures heat accumulation, assuming that plant and insect development largely depends on heat exposure during the growing season, rather than calendar days. It is calculated as the accumulated sum of the difference between daily mean temperature and a species-specific base temperature, below which growth is limited. 1. Winkler Index (WI), also known as the Winkler Scale or Winkler Regions, is commonly applied to classify the climate of wine growing regions based on daily temperature converted to GDD during the growing season (1 April to 31 October in the Northern Hemisphere) [48]. The regions are classified into five climate regions, characterized by increasing temperature levels: from Region I (\(<\)1390 \({}^{\circ}\)C, for example Champagne) to Region V (\(>\)2220 \({}^{\circ}\)C, for example Palermo);
2. Hydroothermic index of Branas, Bernon, and Levadoux (Hyl) developed by [49] considers both precipitation and temperature regimes to estimate the risk of downy mildew for grapevines. An Hyl value below 2500 \({}^{\circ}\)C mm represents a low risk of infection, whereas a value above 5100 \({}^{\circ}\)C mm is considered as a high risk of infection;
3. Flowering date (FD) for maize, also known as R1 or silking stage, begins when female flowers (i.e., silks), first appear outside the husk leaves [50]. It is reached when at least 50% of a field's plants show visible silks. This stage initiates the reproductive phase and is crucial to monitor as it determines the harvest date and therefore its quality and yield. It can be estimated using a modified GDD method, using a 6 \({}^{\circ}\) \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Dataset**} & \multicolumn{2}{c}{**Resolution**} & \multicolumn{2}{c}{**Coverage**} \\ \cline{2-5}  & **Spatial** & **Temporal** & **Spatial** & **Temporal** \\ \hline ERA5 & 0.25\({}^{\circ}\)\(\times\) 0.25\({}^{\circ}\) & Hourly & Global & 1950–Present \\ ERA5-Land & 0.1\({}^{\circ}\)\(\times\) 0.1\({}^{\circ}\) & Hourly & Global & 1950–Present \\ SCOPE Climate & 0.08\({}^{\circ}\)\(\times\) 0.08\({}^{\circ}\) & Daily & France & 1871–2012 \\ FYRE Climate & 0.08\({}^{\circ}\)\(\times\) 0.08\({}^{\circ}\) & Daily & France & 1871–2012 \\ RFHR & 0.01\({}^{\circ}\)\(\times\) 0.01\({}^{\circ}\) & Daily & France & 1979–2021 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Details of the climate reanalysis products (RPs) datasets used in this study. base temperature, with an upper temperature threshold of 30 \({}^{\circ}\)C, starting from the date of planting;
4. Dry days (DDs) Maize is a water-demanding crop and its water requirements vary by growth stage [51]. Peak demand occurs in early reproductive stages; around the pre- and post-flowering stage (June to August). During this period, water stress should be avoided as the drought negatively impacts plant and grain development, ultimately reducing yield [52]. One way to measure dry conditions is by counting dry days;
5. Dormancy breaking (DB) To break dormancy and initiate flowering, most fruit trees need to accumulate a certain amount of cold [53], referred to as chilling requirement (CR) and measured in chilling units (CU). For apple trees, cold needs are satisfied by daily mean temperatures between \(-20\)\({}^{\circ}\)C and \(+20\)\({}^{\circ}\)C, with temperatures close \(0\)\({}^{\circ}\)C being the most effective. To estimate CU, various models are available. Here, a triangular function inspired by the F1 GOLD1 model is used, which has been previously applied to the \"Golden Delicious\" apple [54].