*2.2. Datasets*

#### 2.2.1. Satellite Reflectance Data

The MODIS MCD43A4 Nadir Bidirectional Reflectance Distribution Function (BRDF) Adjusted Reflectance (NBAR) product with a 500 m resolution was used in this study to remove the viewing angle effects from directional reflectivity [42]. A total of 366 images from 1 January 2020 to 31 December 2020 were freely downloaded from the NASA Land Processes Distributed Active Archive Center (LP DAAC, http://lpdaac.usgs.gov (accessed on 10 July 2021)), which were processed to UTM/WGS-84 projection and 500 m resolution. Based on repeated manual tests, missing values of 50 consecutive days would introduce significant errors in reconstructing the VI trajectory. To eliminate errors caused by missing

values in the daily NBAR products, pixels with more than 50 consecutive days of missing data were flagged as poor-quality pixels and excluded from subsequent analysis, which accounted for only 3.34% of the study area. Reflectance in the red, green, near-infrared (NIR), and shortwave infrared (SWIR) bands was used to calculate the different VIs and to further determine the SOS dates.
