Analysis of the Agricultural Applicability of Sentinel-2 NDVI Anomalies: Comparison with Onion Yield

As climate change intensifies yield variation, the South Korean government is developing the Compact Advanced Satellite 500-4 (CAS500-4), whose planned products include vegetation index anomalies.This study offers a pre-operational evaluation of that vegetation index anomaly.Sentinel-2 Level-2A imagery was used to compute year-to-year and five-year normal normalized difference vegetation index (NDVI) anomalies for crop areas in Jeollanam-do, and these were compared with concurrent precipitation and provincial onion-yield departures (2022-2024).The results indicated a general correspondence in the directional trends of the indicators, but also suggested that the strength and nature of this relationship appear to be context-dependent.For instance, in one year, negative NDVI signals were not associated with below-average long-term yields, while in another year, positive environmental indicators coincided with a regional yield decline.Conversely, the long-term anomaly aligned well with the most significant yield loss in a year of presumed sustained pressure, suggesting its utility for diagnosing cumulative stress.The year-to-year NDVI anomaly sensitively detects short-term fluctuations but can be misleading due to base effects or dominant local factors.The five-year normal anomaly, in contrast, provides a more stable diagnosis of cumulative stress.These findings underscore the importance of employing both baselines concurrently to capture short-term impacts and long-term trends as CAS500-4 data become operational.