Three-Dimensional Characteristics Identification of Drought in the Yellow River Basin Based on the Standardized Precipitation Index

Drought is an abnormal hydrological phenomenon characterized by high frequency, long duration, and extensive effect, exerting significant effects on both the ecological environment and the socioeconomic system. This study uses the Standardized Precipitation Index (SPI) to identify drought events in the Yellow River Basin from 1961 to 2021. The identified drought events were analyzed from a three-dimensional perspective to examine their spatial–temporal continuity. Furthermore, this study reveals the spatial and temporal evolution of key drought characteristics, including drought duration, drought area, intensity, density, and centroid position (latitude and longitude). The results indicate the following: (1) A total of 77 drought events have occurred in the Yellow River Basin since 1961, with an average duration of 8.7 months. Of these events, 55.8% lasted longer than the average duration. The average drought area was 50 855 km 2 , and the average drought density was 0.95, indicating a severe overall drought situation. (2) All the drought characteristics showed increasing trends over time (except for drought density). Drought area, drought duration and drought intensity show a strong correlation. Drought events are becoming more severe in the basin. (3) The directions and trajectories of 55 typical drought events in the Yellow River Basin were identified. Overall, they show a reversed migration pattern between the northeastern and southwestern regions of the basin, reflecting a dynamic transition between the Loess Plateau region and Gansu–Ningxia region. This phenomenon is closely associated with variations in El Niño–Southern Oscillation (ENSO) events.