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www.hydrol-earth-syst-sci-discuss.net/5/3247/2008/
doi:10.5194/hessd-5-3247-2008
© Author(s) 2008. This work is distributed
under the Creative Commons Attribution 3.0 License.
Threshold behavior in hydrological systems and geo-ecosystems: manifestations, controls and implications for predictability
1Institute of Water and Environment, Department of Hydrology and River Basin Management, Technische Universität München, Arcisstr. 21, 80330 Munich, Germany
2Univ. of Illinois at Urbana-Champaign, Depts. of Geography and Civil and Environmental Engineering, 220 Davenport Hall, 607 South Mathews Avenue, Urbana, IL 61801, USA
3Department of Water Management, Faculty of Civil Engineering, Delft University of Technology, PO Box 5048, 2600 GA Delft, The Netherlands
Abstract. The aim of this paper is to provide evidence that the dynamics of hydrological systems and geo-ecosystems is often influenced by threshold behavior at a variety of space and time scales. Based on well known characteristics of elementary threshold phenomena we suggest criteria for detecting threshold behavior in hydrological systems. The most important one is intermittence of phenomena, i.e. the rapid switching of related state variables/fluxes from zero to finite values, or existence of behavior regimes where the same process/response appears qualitatively differently at the macroscopic level. From the literature we present several examples for intermittent hydrological phenomena, ranging from overland flow generation in different landscapes, including the effects of hydrophobicity, to soil water flow occurring in the matrix continuum or via preferential pathways, including the case of cracking soils, nonlinear subsurface stormflow response of hillslopes during severe rainfall events, and long-term catchment flooding responses. Since threshold phenomena are often associated with environmental hazards such as floods, soil erosion, and contamination of shallow groundwater resources, we discuss common difficulties that complicate predictions of whether or not they might even occur. Predicting the onset of threshold phenomena requires a thorough understanding of the underlying controls. Through examples we illustrate that threshold behavior in hydrological systems can manifest at (a) the process level, (b) the response level, and (c) the functional level, and explain that the complexity of the underlying controls and of the interacting phenomena that determine threshold behavior become increasingly complex at the higher levels. Finally we provide evidence from field observations and model predictions that show that within an "unstable range" of system states "close" to a threshold, it is difficult to predict whether or not the system will switch behavior, for instance, as a result of the expected rainfall forcing. The term close, in this respect, depends on the expected (rainfall) forcing and the accuracy of our data/knowledge on the macroscopic state of the system.
Discussion Paper (PDF, 9352 KB) Interactive Discussion (Closed, 4 Comments) Final Revised Paper (HESS)
Citation: Zehe, E. and Sivapalan, M.: Threshold behavior in hydrological systems and geo-ecosystems: manifestations, controls and implications for predictability, Hydrol. Earth Syst. Sci. Discuss., 5, 3247-3312, doi:10.5194/hessd-5-3247-2008, 2008. Bibtex EndNote Reference Manager XML
