## 2 Data and Methods
### Data Processing Method
#### 2.2.3 Data Acquisition and Preparation  
The Terra MODIS NDVI product (MOD13Q1, collection v006) with 250 m ground resolution and 16-day revisit cycle was downloaded from the National Aeronautics and \begin{table}
\begin{tabular}{c c c c} \hline
**Category** & **NDVI Anomaly Values (\%)** & **Category** & **NDVI Anomaly Values (\%)** \\ \hline Extreme drought & Below \(-50\) & Mild wet & 0 to 10 \\ Severe drought & \(-25\) to \(-50\) & Moderate wet & 10 to 25 \\ Moderate drought & \(-10\) to \(-25\) & Severe wet & 25 to 50 \\ Mild drought & 0 to \(-10\) & Extreme wet & Above 50 \\ \hline \end{tabular}
\end{table} 
Table 1: Categorization of dryness/wetness of normalized difference vegetation index (NDVI) anomaly values. Space Administration Earth Observing System Dataset and Information System ([[https://ladsweb.modaps.eosdis.nasa.gov](https://ladsweb.modaps.eosdis.nasa.gov)]([https://ladsweb.modaps.eosdis.nasa.gov](https://ladsweb.modaps.eosdis.nasa.gov)), accessed on 17 October 2017) for drought index. The daily climatic data, including precipitation, air temperature, net surface radiation, wind speed, snow depth, and dew point temperature, for the period of 2003-2018 were retrieved from the European Centre for Medium-Range Weather Forecast (ECMWF) products. The ECMWF provides global gridded three-hour time-varying climatology products ([[http://www.ecmwf.int/research/era](http://www.ecmwf.int/research/era)]([http://www.ecmwf.int/research/era](http://www.ecmwf.int/research/era)), accessed on 10 December 2018) with a spatial resolution of 0.125\({}^{\circ}\)\(\times\) 0.125\({}^{\circ}\). The data provided in the NetCDF-4 (network Common Data Form) file format was processed and converted to a common img. format in their respective units as mentioned in Table 2.  
The vegetation index is an important input variable for the BEPS model. We used collection 6 (C6) leaf area index (LAI) data from the MODIS as input for vegetation dynamics that constrain BEPS for a more realistic estimation of NPP at a regional scale. The MODIS LAI product (MCD15A3H) with 4-day temporal and 500 m spatial resolution from NASA's Terra and Aqua satellites was obtained through the Earth data search client website ([[https://doi.org/10.5067/MODIS/MCD15A3H.006](https://doi.org/10.5067/MODIS/MCD15A3H.006)]([https://doi.org/10.5067/MODIS/MCD15A3H.006](https://doi.org/10.5067/MODIS/MCD15A3H.006)), accessed on 1 January 2019). Data gaps in the 4-day temporal MODIS LAI were interpolated to daily intervals from the original 4 days raster using the direct linear interpolation method for 2003-2018. For the BEPS model, land cover information was obtained from the European Space Agency (ESA) Climate Change Initiative Land Cover (CCI-LC) product through the project's website ([[http://maps.elie.ucl.ac.be/CCI/viewer/download.php](http://maps.elie.ucl.ac.be/CCI/viewer/download.php)]([http://maps.elie.ucl.ac.be/CCI/viewer/download.php](http://maps.elie.ucl.ac.be/CCI/viewer/download.php)), accessed on 17 June 2019). In addition, an additional layer of percent tree cover at a spatial resolution of 250 m [56] and the available soil water-holding capacity (AWC), the 30 m digital elevation data (DEM), and the latitude data were also major input parameters for the BEPS model (Figure 2). Wilting point and field capacity at a resolution of 0.083\({}^{\circ}\)\(\times\) 0.083\({}^{\circ}\) were downloaded from the International Geosphere-Biosphere Program, Data and Information System (IGBP-DIS; [[https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id=569](https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id=569)]([https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id=569](https://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id=569)), accessed on 15 January 2019) to calculate the AWC.