Scale effects and driving mechanisms of flood in a multilevel sub-basin perspective - A case study of Haihe River Basin, China

Abstract

Amidst the escalating dynamics of climate change, there has been a notable global uptick in the frequency and intensity of extreme meteorological phenomena. The resultant basin-wide flooding, triggered by extreme rainfall events, poses a formidable challenge to regional security and stability. In an effort to transcend the constraints inherent in previous studies that employed single-scale or raster-based approaches, the present research adopts a novel methodology by utilizing sub-watersheds as the fundamental units for delineation, thereby facilitating a multi-scale hierarchical analysis. This approach has been meticulously applied to the delineation of eight distinct sub-basins within the Haihe River Basin, with scales varying from 100 to 40,000 km², serving as a robust case study. The analytical framework of this study is both comprehensive and multidisciplinary, incorporating advanced techniques such as spatial autocorrelation analysis, Spearman regression analysis, and random forest modeling. These methodologies are employed with the objective of unraveling the complex mechanisms influencing flood phenomena and elucidating the scale-dependent dynamics that drive flood patterns across various scales. Empirical results from this study reveal a distinct spatial distribution of flood occurrences within the Haihe River Basin, characterized by a higher frequency in the eastern regions and a lower frequency in the western areas. Notably, flood aggregation predominantly manifests in designated flood storage zones and along riverine corridors. This research also accentuates the significant scale effects in flood distribution, particularly highlighting that the impact of spatial indicators reaches its zenith at the 300 km² sub-basin scale. Furthermore, the study delineates the differential impacts of topographic, hydrological, and land cover elements across varying basin scales. It is observed that these elements exert their most pronounced effects at large, medium, and small basin scales respectively. Intriguingly, the contribution rates of these indicators fluctuate across different sub-basin scales, with surface cover emerging as the most influential factor, followed by topographical features and hydrographic conditions. These insights offer invaluable guidance for the strategic prioritization and targeted management of flood mitigation efforts within river basins, thereby contributing significantly to the enhancement of regional resilience against hydrological disasters. This study not only advances our understanding of flood dynamics but also underscores the critical importance of scale-aware strategies in the effective management of water resources in the face of climate change.