Watersheds As Complex Systems: Looking For Emergent Properties In Hydrological Behavior

Murugesu Sivapalan, Professor of Geography and Civil & Environmental Engineering, UIUC

Watersheds are self-organized natural entities, consisting of interacting, inter-dependent parts, e.g., climate, soils, vegetation, topography (hillslopes), and the river network. They are characterized by strong (usually non-linear) interactions between the parts, including significant thresholds, and complex feedback loops that make it difficult to distinguish between cause and effect. Much of the focus on past hydrological research has focused on developing a predictive understanding of individual processes, and then combining them within a watershed modeling framework to mimic and learn from past observations in individual watersheds. Attempts to decipher the underlying, repeatable signatures of hydrologic responses in individual watersheds and similarities between watersheds and interpreting these in terms of the underlying climate, soil, vegetation and topographic controls are less common. Increasingly the notion that watersheds are complex systems which contribute to the formation of emergent patterns in the landscape – river network structure, soil catena, vegetation organization – and patterns in observed hydrological behavior. I will present a few examples of these “emergent properties” in hydrological responses to rainfall and attempts to understand the underlying physical controls.

Audio Slides