The Global Atmospheric River Network: A Complex Network Approach to Global Moisture Transport Dynamics

The increasing frequency and severity of hydrological extremes, such as heavy precipitation events, are significant challenges for human-environmental systems. Atmospheric rivers (ARs) are key drivers of these extremes, but the complex transport patterns of ARs at global scale remain underexplored. Our research introduces a novel network-based approach to studying global AR dynamics, applying methods from complexity science to reveal the “global road network” of ARs.

In analogy to terrestrial river networks, the pathways that ARs follow through the Earth’s atmosphere can be effectively represented by a transport network. Generally, the paradigm of complex networks encodes interactions between the units of a system through interlinked nodes. Recent applications illustrate that complex networks have provided novel insights into climate teleconnection patterns, synchronization of extremes and vegetation-atmosphere feedbacks. We draw on the vast array of existing methods from complex network theory to reveal the global atmospheric river network. We define it on a hexagonal grid to avoid distortions due to the Earth’s spherical geometry. Multiple AR catalogs can be integrated seamlessly. To quantitatively assess the significance of a transport property, the framework is equipped with a hierarchy of data-adaptive null models that are based on random walker ensembles.

We dissect the global transport infrastructure of ARs which reveals prominent AR pathways, regions of complex multi-directional transport, the predictability of single AR tracks, and scale-dependent spatial clusters. We demonstrate that there exists complexity above and beyond the previously identified four main branches of AR transport. These main oceanic bands can be decomposed into significant sub-branches. Exploiting all these novel tools to characterise AR transport, we unveil how the AR network is evolving in a changing climate. This talk underscores the potential of complexity science to advance our understanding of ARs as critical components of the integrated human-Earth system.