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 monthly discharges of the 30 'best' flow series and a total of 52 flow series containing unaltered flow data were selected to represent baseline flow conditions for tributaries throughout the basin. Metrics representing magnitude, duration and frequency components of flow were used to identify hydrologic differences across the basin. A total of six natural flow regimes were identified in the Ebro Basin, using a Ward cluster method. The flow patterns identified and their spatial distribution largely corresponded with climatic zones previously reported for the Ebro Basin, with regime types ranging from pluvio-oceanic in the western part of the basin to Mediterranean in the eastern region. Geologic characteristics of the catchment and altitude of headwaters were also found to play an important role in defining flow regime type. A 19-hydrologic variable subset was used to explain main hydrologic differences among groups (such as magnitude and frequency of extreme flow conditions or magnitude and variance of average flow conditions). However, stepwise discriminant analysis was not able to identify consistent subsets of hydrologic variables that adequately identified the six natural flow regime types in this basin. Canonical discriminant analysis was useful to understand class separation and for the interpretation of results.

Flow prediction in ungauged basins is an important task for water resources planning and management, and remains a fundamental challenge for hydroecological research. Based on a previous classification of streams and rivers in the Ebro River basin (Spain), where six natural flow‐regime types were identified, we apply a new predictive approach of the flow regime type based on climatic and physiographic descriptors. We used a set of easily available environmental variables as discriminant parameters: annual precipitation, annual evapotranspiration, annual air temperature, elevation, catchment area, drainage density and geology. A stepwise landscape‐based classification procedure consisting of several stepwise discriminant analyses and canonical discriminant analyses allocated a set of sites with poor or no natural flow data into the flow types defined. Misclassification rates obtained by cross‐validation ranged between 1.12% and 11.9%. Additionally, the ecological soundness of the proposed regionalization was tested by the concordance between macroinvertebrate communities and the proposed classification using NMDS and ANOSIM. NMDS resulted in a clear separation of sites into five NFR classes with available macroinvertebrate data, and ANOSIM found significant differences in macroinvertebrate communities among classes. Copyright © 2014 John Wiley & Sons, Ltd.

Ecological limits of hydrological alteration (ELOHA) framework aims to set limits of hydrologic alteration based on empirical hydroecological relationships built along flow impairment gradients. These relationships can be specific for different natural flow regime types. The object of our study is testing the ELOHA method in the Ebro River Basin. Seven flow alteration–ecological response curves were obtained in the present study as preliminary guidelines for developing and calibrating environmental flow standards in the Ebro River Basin. For continental Mediterranean‐pluvial flow regime mean monthly flow in March was related to Plecoptera abundance (ELOHAs ±21% from baseline), and high flow magnitude and frequency were closely related to Plecoptera, Ephemeroptera and Trichoptera richness (ELOHAs for high flow magnitude and frequency were +18 and +54% the reference central value respectively). For nivo‐pluvial flow regime, high flow magnitude was found indicative of macroinvertebrate biodiversity and Coleoptera abundance (ELOHAS −12 and +23% from central reference value respectively). And for pluvio‐oceanic flow regime, mean monthly flow in January was indicative of the proportion of Gastropoda, Oligochaeta and Diptera taxa (GOLD index) (ELOHA +17% from baseline). These hydrological limits are endorsed by recent international reference works. Flow alteration–ecological relationships presented here were constructed from real monthly flow data records and macroinvertebrate samples at family level. ELOHA values obtained in this study pretend to be a starting point for implementing an environmental flow regime program in the Ebro River Basin. Copyright © 2016 John Wiley & Sons, Ltd.

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