## 2 Materials and Methods
### Data Sources and Processing
#### 2.2.1 Data for Constructing the VMFDI  
VPD, SM, and SIF have been verified for effective drought monitoring from different perspectives [24; 38]. To establish the VMFDI, VPD, SM, and SIF data from 01/2003 to 12/2020 were collected (Table 1). Figure 1: Location and land use of study area. Figure 2: Technical flowchart. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Data Type** & **Production** & **Spatial** & **Temporal** & **Unit** & **Data Period** & **Source** \\  & **/Title** & **Resolution** & **Resolution** & **Resolution** & **Data Period** & **Source** \\ \hline VPD & HMIC & 1 km & Monthly & hPa & 2003–2020 & [[http://data.ipdc.ac.cn](http://data.ipdc.ac.cn)]([http://data.ipdc.ac.cn](http://data.ipdc.ac.cn)) (accessed on 14 May 2024) \\ SM & SMCII.0 & 30\({}^{\prime\prime}\) & Daily & 0.001 m\({}^{3}\)/m\({}^{3}\) & 2000–2020 & [[http://data.ipdc.ac.cn](http://data.ipdc.ac.cn)]([http://data.ipdc.ac.cn](http://data.ipdc.ac.cn)) (accessed on 14 May 2024) \\ SIF & COSIF & 0.05\({}^{\circ}\) & Monthly &
\begin{tabular}{c} mW m\({}^{-2}\)um\({}^{-1}\) \\ sr\({}^{-1}\) \\ \end{tabular} & 2000-2023 & [[https://data.globalobserv.edu/data/](https://data.globalobserv.edu/data/)]([https://data.globalobserv.edu/data/](https://data.globalobserv.edu/data/)) (accessed on 14 May 2024) \\ SPEI & SPEI base v2.8 & 0.5\({}^{\circ}\) & Monthly & / & 1901–2021 & (accessed on 15 May 2024) \\ TWS & GTWS-MLwc & 0.25\({}^{\circ}\) & Monthly & mm & 1940–2022 & [[https://model.org/records/1004927](https://model.org/records/1004927)]([https://model.org/records/1004927](https://model.org/records/1004927)) \\ PRE & Precipitation & 1 km & Monthly & 0.1 mm & 1901–2022 & [[https://www.ipdc.ac.cn/2h-ms/data/](https://www.ipdc.ac.cn/2h-ms/data/)]([https://www.ipdc.ac.cn/2h-ms/data/](https://www.ipdc.ac.cn/2h-ms/data/)) & \\ ET & MOD16A2 & 500 m & 8-day & mm & & \\ ENT & MOD13A1 & 500 m & 16-day & / & 0201–2023 & [[https://developers.google.cn/earth-](https://developers.google.cn/earth-)]([https://developers.google.cn/earth-](https://developers.google.cn/earth-)) \\ SMPI & MOD17A2H & 500 m & 8-day & gC m\({}^{-2}\) & 02/2000–42/2023 & \multicolumn{3}{c}{engine/datasets} \\ LAI & MOD15A2H & 500 m & 8-day & Area fraction & 02/2000– (accessed on 17 May 2024) \\ Land & LC,TypeI & 500 m & Yearly & / & 01/2001–01/2022 & \multicolumn{3}{c}{engine/datasets} \\ Maize Wheat & China/CropArenalkm & 1 km & Yearly & / & 01/2003–2019 & \multicolumn{3}{c}{(accessed on 17 May 2024)} \\  & ChuaWhent/Maize10 & 10 m & Yearly & / & 2020 & \multicolumn{3}{c}{(accessed on 04/07/2024 and 16 July 2024)} \\ \end{tabular}
\end{table} 
Table 1: Description of related datasets used in this study. VPD is an important indicator reflecting regional meteorological drought and inflowing vegetation growth, defined as the difference between saturated vapor pressure and actual vapor pressure at a specific temperature. In this study, monthly VPD data were extracted from the HiMIC-Monthly database, which provides 1 km high-resolution atmospheric moisture data for China in 2003-2020 [45]. The dataset has an accuracy of over 0.96, with a root mean square error and mean absolute error within acceptable ranges [46]. SM data were obtained from the SMCI1.0 (Soil Moisture of China by in situ data, version 1.0) of the National Tibetan Plateau/Third Pole Environment Data Center [25]. SMCI1.0 provides daily soil moisture at 10 cm depth intervals up to 100 cm, with a spatial resolution of ~1 km. The data are derived from machine learning based on the observed soil moisture from 1648 stations of the China Meteorological Administration, ERA5-land, leaf area index, land cover type, topography, and soil properties [38; 47]. In this study, monthly SM was summed from daily data, averaged to the 0-40 cm soil depth, which effectively reflects agricultural drought. The data were downscaled to 1 km via the nearest neighbor sampling method to match VPD resolution. SIF is less influenced by soil background and clouds and directly reflects plant photochemical activity.