Classification of natural flow regimes in the Ebro basin (Spain) by using a wide range of hydrologic parameters

This paper presents a classification of different natural flow regimes found in Ebro basin, one of the largest in the Mediterranean region.Determination of flow regimes was based on multivariate analyses using long-term discharge series of unaltered flow data. Mean monthlydischarges of the 30 ‘best’ flow series and a total of 52 flow series containing unaltered flow data were selected to represent baseline flowconditions for tributaries throughout the basin. Metrics representing magnitude, duration and frequency components of flow were used toidentify hydrologic differences across the basin. A total of six natural flow regimes were identified in the Ebro Basin, using a Ward clustermethod. The flow patterns identified and their spatial distribution largely corresponded with climatic zones previously reported for the EbroBasin, with regime types ranging from pluvio-oceanic in the western part of the basin to Mediterranean in the eastern region. Geologiccharacteristics of the catchment and altitude of headwaters were also found to play an important role in defining flow regime type. A19-hydrologic variable subset was used to explain main hydrologic differences among groups (such as magnitude and frequency ofextreme flow conditions or magnitude and variance of average flow conditions). However, stepwise discriminant analysis was not able to identifyconsistent subsets of hydrologic variables that adequately identified the six natural flow regime types in this basin. Canonical discriminant analysiswas useful to understand class separation and for the interpretation of results. Copyright © 2012 John Wiley & Sons, Ltd.