## 3 Results
### Site-Level Start of Season in Evergreen Needle-Leaf Forest  
We compared ENF_SOSEC in Sodankyla and Hyytiala with JSBACH-simulated dates based on the two different sets of meteorological drivers: ENF_SOSmod,loc and ENF_SOSmod (Figure 3). ENF_SOSEC ranged from mid-March to mid-April (33 days) at Hyytiala, and from the end of April to the beginning of May (14 days) at Sodankyla. The ENF_SOSmod,loc was too early in comparison with observations (Table 3). The bias was twice as large for Sodankyla as compared to Hyytiala and correlations between ENF_SOSmod,loc and ENF_SOSEC were not significant. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline
**Site Name** & \begin{tabular}{c} **Number of** \\ **Observations** \\ \end{tabular} & \begin{tabular}{c} **Mean Bud** \\ **Break (Doy)** \\ \end{tabular} & \begin{tabular}{c} **Mean DBF_SOSat** \\ **(Doy)** \\ \end{tabular} & \begin{tabular}{c} **R2** \\ \end{tabular} & \begin{tabular}{c} \(p\) \\ \end{tabular} & \
\begin{tabular}{c} **RMSE (d)** \\ \end{tabular} &
\begin{tabular}{c} **Bias (d)** \\ \end{tabular} \\ \hline Aulanko & 5 & 127.2 & 122.8 & 0.28 & 0.362 & 6.6 & \(-\)4.4 \\ Vesjako & 7 & 131.6 & 126.6 & 0.01 & 0.807 & 7.0 & \(-\)5.0 \\ Koli & 7 & 133.7 & 136.8 & 0.40 & 0.127 & 5.7 & 3.1 \\ Kamus & 7 & 134.1 & 128.9 & 0.01 & 0.832 & 10.1 & \(-\)5.3 \\ Varrió & 7 & 155.0 & 160.1 & 0.43 & 0.111 & 8.6 & 5.1 \\ Kolari & 6 & 140.8 & 145.5 & 0.46 & 0.137 & 7.3 & 4.7 \\ Saariselka & 4 & 154.3 & 154.3 & 0.66 & 0.191 & 5.5 & 0.0 \\ Kevo & 5 & 155.4 & 155.8 & 0.35 & 0.294 & 4.4 & \(-\)0.4 \\ Site-means & 8 & 141.5 & 141.4 & 0.94 & 0.001 & 4.4 & 0.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison between DBF_SOSSat and phenological observations of bud break of birch for sites in Finland. A positive bias means that the detected SOS is late compared to observations. Figure 3: Comparison of the start of season in evergreen needle-leaf forest determined from eddy covariance measurements (ENF_SOSEC) and satellite observations (ENF_SOSsat), together with JSBACH model-derived dates for 2001 to 2010 in (**a**) Hyytiala, southern Finland and (**b**) Sodankyla, northern Finland. The start of season from JSBACH was determined from model runs using both REMO-generated bias-corrected meteorological data (ENF_SOSmod) and local site observations (ENF_SOSmod,loc). The bias between ENF_SOSEC and the start of season from the regional run, ENF_SOSmod, was much smaller than the bias between ENF_SOSEC and ENF_SOSmod,loc. Again, the early bias was larger for Sodankyla than for Hyytiala. Correlations between ENF_SOSmod-modelled dates with ENF_SOSEC were significant only for Hyytiala (Table 3), whereas the year-to-year anomalies correlated significantly for both sites (R\({}^{2}\) = 0.51, \(p\) = 0.001, \(N\) = 19). An investigation of the reasons for differences in ENF_SOSmod and ENF_SOSmod,loc in Sodankyla showed that GPP simulated with JSBACH followed closely the development of air temperature during the springs, 2004 and 2008 (Figures 4 and 5). However, the simulated GPP showed a higher increase during warm spells in spring than the GPP from CO2 flux measurements. This was even more pronounced for the JSBACH GPP simulations with the local driving data than for simulations with regional climate data (Figure 4a,b). The local temperature observations indicated warm spells in 2004 around the day of year (doy) 96, 108 and 119. Therefore, the simulated GPP exceeded the threshold for the start of season earlier than the observed GPP. Consequently, the JSBACH-simulated ENF_SOSmod,loc and ENF_SOSmod occurred earlier than ENF_SOSEC, on day 96 and 117, respectively. Instead, ENF_SOSEC was delayed by cold spells that occurred around day 110 and 115, and it was only observed on day 121. Modelled snow depth from JSBACH simulations with both local and regional meteorological drivers was lower than the observed snow depth and the snow melted earlier in the model (Figures 4 and 5c).