Evaluation of Vegetation Indexes and Green-Up Date Extraction Methods on the Tibetan Plateau

The vegetation green-up date (GUD) of the Tibetan Plateau (TP) is highly sensitive to climate change. Accurate estimation GUD essential for understanding dynamics and stability terrestrial ecosystems their interactions with climate. usually determined from a time-series indices (VIs). adoption different VIs extraction methods can lead GUDs. However, our knowledge uncertainty in these GUDs on TP still limited. In this study, we evaluated performance 2003 2020. were six Moderate Resolution Imaging Spectroradiometer (MODIS) derived VIs: normalized difference index (NDVI), enhanced (EVI), infrared (NDII), phenology (PI), (NDPI), greenness (NDGI). Four (?max, CCRmax, G20, RCmax) applied individually each VI determine GUD. obtained all showed similar patterns early eastern late western plateau, trend advancement postponement plateau. accuracy was by comparison ground-observed 19 agrometeorological stations. Our results show that two snow-free VIs, NDGI NDPI, had better than snow-calibrated conventional NDVI EVI. Among gave highest when combined four methods. Based NDGI, extracted CCRmax method found have consistency (r = 0.62, p < 0.01, RMSE 11 days, bias ?3.84 days) ground observations. also preseason snow-covered site-years 0.71, 10.69 ?4.05 days), indicating its optimal resistance snow cover influence. comparison, NDII PI hardly captured seriously affected cover, as indicated negative correlation coefficient ?0.34, 0.1), high (RMSE 50.23 ?24.25 days).