Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/hess-2016-639
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
19 Dec 2016
Review status
This discussion paper is under review for the journal Hydrology and Earth System Sciences (HESS).
Regional regression models of percentile flows for the contiguous US: Expert versus data-driven independent variable selection
Geoffrey Fouad1, André Skupin2, and Christina L. Tague3 1Geography Program, Monmouth University, West Long Branch, NJ, USA
2Department of Geography, San Diego State University, San Diego, CA, USA
3Bren School of Environmental Science and Management, University of California, Santa Barbara, CA, USA
Abstract. Percentile flows are statistics derived from the flow duration curve (FDC) that describe the flow equaled or exceeded for a given percent of time. These statistics provide important information for managing rivers, but are often unavailable since most basins are ungauged. A common approach for predicting percentile flows is to deploy regional regression models based on gauged percentile flows and related independent variables derived from physical and climatic data. The first step of this process identifies groups of basins through a cluster analysis of the independent variables, followed by the development of a regression model for each group. This entire process hinges on the independent variables selected to summarize the physical and climatic state of basins. Distributed physical and climatic datasets now exist for the contiguous United States (US). However, it remains unclear how to best represent these data for the development of regional regression models. The study presented here developed regional regression models for the contiguous US, and evaluated the effect of different approaches for selecting the initial set of independent variables on the predictive performance of the regional regression models. An expert assessment of the dominant controls on the FDC was used to identify a small set of independent variables likely related to percentile flows. A data-driven approach was also applied to evaluate two larger sets of variables that consist of either (1) the averages of data for each basin or (2) both the averages and statistical distribution of basin data distributed in space and time. The small set of variables from the expert assessment of the FDC and two larger sets of variables for the data-driven approach were each applied for a regional regression procedure. Differences in predictive performance were evaluated using 184 validation basins withheld from regression model development. The small set of independent variables selected through expert assessment produced similar, if not better, performance than the two larger sets of variables. A parsimonious set of variables only consisted of mean annual precipitation, potential evapotranspiration, and baseflow index. Additional variables in the two larger sets of variables added little to no predictive information. Regional regression models based on the parsimonious set of variables were developed using 734 calibration basins, and were converted into a tool for predicting 13 percentile flows in the contiguous US. Supplementary Material for this paper includes an R graphical user interface for predicting the percentile flows of basins within the range of conditions used to calibrate the regression models. The equations and performance statistics of the models are also supplied in tabular form.

Citation: Fouad, G., Skupin, A., and Tague, C. L.: Regional regression models of percentile flows for the contiguous US: Expert versus data-driven independent variable selection, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-639, in review, 2016.
Geoffrey Fouad et al.
Geoffrey Fouad et al.
Geoffrey Fouad et al.

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Short summary
Regression models were developed to predict streamflow variables (i.e. flow duration curve percentile flows) for the contiguous US. Over 35 independent variables were evaluated, but only three selected through an expert assessment performed better than most combinations of the other variables. Simple regression models consisting of annual precipitation, potential evapotranspiration, and baseflow were converted into a tool for predicting percentile flows for ungauged basins in the contiguous US.
Regression models were developed to predict streamflow variables (i.e. flow duration curve...
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