Assessing the simple dynamical systems approach in a Mediterranean context: application to the Ardèche catchment (France)

摘要

This study explores how catchment heterogeneity and variability can besummarized in simplified models, representing the dominant hydrologicalprocesses. It focuses on Mediterranean catchments, characterized byheterogeneous geology, pedology and land use, as well as steep topographyand a rainfall regime in which summer droughts contrast with high-rainfallperiods in autumn. The Ardèche catchment (Southeast France), typical ofthis environment, is chosen to explore the following questions: (1) can sucha Mediterranean catchment be adequately characterized by a simple dynamicalsystems approach and what are the limits of the method under suchconditions? (2) what information about dominant predictors of hydrologicalvariability can be retrieved from this analysis in such catchments?In this work we apply the data-driven approach of Kirchner (2009) toestimate discharge sensitivity functions that summarize the behaviour of foursub-catchments of the Ardèche, using low-vegetation periods(November–March) from 9 years of measurements (2000–2008) from operationalnetworks. The relevance of the inferred sensitivity function is assessedthrough hydrograph simulations, and through estimating precipitation ratesfrom discharge fluctuations. We find that the discharge sensitivity functionis downward-curving in double-logarithmic space, thus allowing furthersimulation of discharge and non-divergence of the model, only duringlow-vegetation periods. The analysis is complemented by a Monte Carlosensitivity analysis showing how the parameters summarizing the dischargesensitivity function impact the simulated hydrographs. The resultingdischarge simulation results are good for granite catchments, which arelikely to be characterized by shallow subsurface flow at the interfacebetween soil and bedrock. The simple dynamical system hypothesis worksespecially well in wet conditions (peaks and recessions are well modelled).On the other hand, poor model performance is associated with summer and dryperiods when evapotranspiration is high and low-flow discharge observationsare inaccurate. In the Ardèche catchment, inferred precipitation ratesagree well in timing and amount with observed gauging stations and SAFRANclimatic data reanalysis during the low-vegetation periods. The model shouldfurther be improved to include a more accurate representation of actualevapotranspiration, but provides a satisfying summary of the catchmentfunctioning during wet and winter periods.