Spatial Compounding of Flash Droughts at different time scales in the Huaihe River Basin, China

Flash droughts, characterized by rapid onset and intensification, have received increasing attention. Previous studies focused on their identification, evolution, and climatic drivers, while the spatial co-occurrence and connectivity of flash droughts (i.e., compound flash droughts) remain poorly understood, limiting regional impact assessment. Based on a case study of the Huaihe River Basin, we develop a framework for identifying compound flash drought events and analyzing their spatial connectivity. Utilizing multi-dimensional flash drought indicators, connectivity and clustering analyses are conducted at annual and seasonal scales, and the dominant driving factors are further examined. The results revealed spatial heterogeneity of compound flash droughts across the basin. High-connectivity areas are concentrated in the northern, north-western, and central regions, with substantially lower connectivity in the southeast. The basin is divided into four types of compound flash droughts based on annual clustering. The high-intensity and high-deficit types are primarily located in the northern and northwestern regions, forming a southeast–northwest increasing gradient. Autumn exhibits the strongest spatial differentiation and the most frequent and widespread compound flash droughts based on seasonal clustering. The dominant driving factors differ among compound flash drought types. This study advances flash drought understanding from a spatial organization and connectivity perspective. It provides new support for basin-scale drought risk assessment and water resources management.