Assessment of spatiotemporal compound drought propagation in the Nakdong River basin, South Korea, using a multi-layer complex network

초록

Study region: The Nakdong River basin (NRB), one of South Korea’s major river basins, exhibits significant spatial and temporal variability in drought propagation. Study focus: Drought is a continuous disaster that evolves both temporally and spatially. This complex evolution process is defined as drought propagation. Previous studies have typically addressed the propagation mechanisms between different drought categories and the spatial dispersion of individual drought types as independent processes. To overcome these limitations, a multi-layer complex network approach was adopted to evaluate the spatiotemporal compound propagation of meteorological and hydrological droughts in the NRB. Furthermore, clustering of sub-watersheds by topological indicators was used to highlight distinct physical dynamics across different clusters. New hydrological insights into the region under study: A total of 272 sub-watersheds in the NRB were classified into sources (28%) and sinks (72%) based on the propagation strength. Source watersheds were clustered as C1(high-intensity and multi-direction), C2(uni-direction), and C3(multi-direction), while the sink watersheds were grouped into C4(multi-direction), C5(uni-direction), and C6(high-intensity and uni-direction). Spatial analysis showed that watersheds in C1 were concentrated in the southeast, whereas those in C6 predominated in the northwest. This distribution underscored the need for proactive monitoring in the southeast and enhanced resilience in the vulnerable northwest. The propagation features were differentially associated with distinct topological indicators. Attenuation was significantly correlated with source out-strength, and sink entropy, lag with sink in-strength, and lengthening with source out-strength, sink in-strength and sink entropy. These associations demonstrated that the propagation features are linked to the structural role of each sub-watershed within the network, which conventional complex network or probabilistic approaches cannot detect. By quantifying spatiotemporal compound propagation from a network perspective, this study supports tailored drought management strategies including source control, impact mitigation, and proactive implementation of early warning systems.

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