## 2 Materials and Methods
### Methods
#### 2.2.2 Improvement of the Autumn Phenology Model  
The traditional autumn phenology model is based on low temperature accumulation, known as the cold degree day (CDD) model [10]. Considering the potential impacts of SOS and growing season GPP on EOS [9; 15], we incorporated SOS, GPP, and their combination \begin{table}
\begin{tabular}{c c c} \hline
**Dataset** & **Spatial/Temporal Resolution** & **Data Access** \\ \hline MODIS NDVI (MVD13C1) & 0.05\({}^{\circ}\)/16-day & [[https://ladsweb.modaps.cosdis.nasa.gov](https://ladsweb.modaps.cosdis.nasa.gov)]([https://ladsweb.modaps.cosdis.nasa.gov](https://ladsweb.modaps.cosdis.nasa.gov)) (accessed on 29 January 2025) \\ MODIS Tem (MOD11C2) & 0.05\({}^{\circ}\)/8-day & [[https://ladsweb.modaps.cosdis.nasa.gov](https://ladsweb.modaps.cosdis.nasa.gov)]([https://ladsweb.modaps.cosdis.nasa.gov](https://ladsweb.modaps.cosdis.nasa.gov)) (accessed on 29 January 2025) \\ Revised FC-UC-CPP & 0.05\({}^{\circ}\)/8-day & [[https://ladsweb.modaps.cosdis.nasa.gov](https://ladsweb.modaps.cosdis.nasa.gov)]([https://ladsweb.modaps.cosdis.nasa.gov](https://ladsweb.modaps.cosdis.nasa.gov)) (accessed on 29 January 2025) \\ GPP based on NIRW & 0.05\({}^{\circ}\)/monthly & [[https://ladsweb.modaps.rosdis.nasa.gov](https://ladsweb.modaps.rosdis.nasa.gov)]([https://ladsweb.modaps.rosdis.nasa.gov](https://ladsweb.modaps.rosdis.nasa.gov)) (accessed on 29 January 2025) \\ CLASS PAPAR & 250 nm/8-day & [[http://glasss.amad.edu/](http://glasss.amad.edu/)]([http://glasss.amad.edu/](http://glasss.amad.edu/)) (accessed on 29 January 2025) \\  & 0.05\({}^{\circ}\)/daily & [[http://glasss.amad.edu/](http://glasss.amad.edu/)]([http://glasss.amad.edu/](http://glasss.amad.edu/)) (accessed on 29 January 2025) \\ ERA5 ET & 0.1\({}^{\circ}\)/monthly & [[https://cds.climate.opernicus.eu/datasets](https://cds.climate.opernicus.eu/datasets)]([https://cds.climate.opernicus.eu/datasets](https://cds.climate.opernicus.eu/datasets)) (accessed on 29 January 2025) \\ China FET & 1 km/monthly & [[http://luesg.godalta.ca](http://luesg.godalta.ca)]([http://luesg.godalta.ca](http://luesg.godalta.ca)) (accessed on 29 January 2025) \\ China Per & 1 km/monthly & [[https://dos.org/10.5281/zenodo.31149](https://dos.org/10.5281/zenodo.31149)]([https://dos.org/10.5281/zenodo.31149](https://dos.org/10.5281/zenodo.31149)) (accessed on 29 January 2025) \\ MODIS land use (MCD12C1) & 0.05\({}^{\circ}\)/yearly & [[https://ladsweb.modaps.cosdis.nasa.gov](https://ladsweb.modaps.cosdis.nasa.gov)]([https://ladsweb.modaps.cosdis.nasa.gov](https://ladsweb.modaps.cosdis.nasa.gov)) (accessed on 29 January 2025) \\ \hline \end{tabular}
\end{table} 
Table 1: The spatiotemporal resolution and data accessibility details of the satellite datasets. Figure 2: The framework of NEP improvement. SOC refers to soil organic carbon density. into the CDD model, naming the models \(\text{CDD}_{\text{S}}\), \(\text{CDD}_{\text{G}}\), and \(\text{CDD}_{\text{SG}}\), respectively. The CDD model hypothesizes that the cooling degree starts to accumulate when the daily temperature drops below the critical temperature and stops on the day of foliar senescence [10]. The formula was as follows:  
\[CDD_{d}=\sum_{d=d_{0}}^{d_{y}}\text{max}\text{ }\left(T_{th}-T_{(d)},\text{ }0\right) \tag{1}\]  
\[EOS=d_{y},\text{ }if\text{ }CDD_{d}\geq CDD_{th} \tag{2}\]  
where \(CDD_{d}\) represents the accumulated cooling degree from day \(d_{0}\) to day \(d_{y}\); \(CDD_{th}\) is the required threshold upon which EOS occurs; \(T_{th}\) is the critical temperature; \(T_{(d)}\) is the mean daily temperature on day d; and \(d_{0}\) is set to 1 July [23]. The model has two free parameters, \(T_{th}\) and \(CDD_{th}\). For the \(\text{CDD}_{\text{S}}\) and \(\text{CDD}_{\text{G}}\) models, \(CDD_{th}\) depends on SOS and the growing season GPP (Equations (3) and (4)), while the \(CDD_{th}\) for \(\text{CDD}_{\text{SG}}\) model is linearly linked to both SOS and the growing season GPP (Equation (5)).