Smooth regional estimation of low-flow indices: physiographical space based interpolation and top-kriging

A. Montanari,A. Castellarin,S. Castiglioni,G. Blöschl,G. Laaha,J. O. Skøien

doi:10.5194/hess-15-715-2011

Abstract

Abstract. Recent studies highlight that spatial interpolation techniques of point data can be effectively applied to the problem of regionalization of hydrometric information. This study compares two innovative interpolation techniques for the prediction of low-flows in ungauged basins. The first one, named Physiographical-Space Based Interpolation (PSBI), performs the spatial interpolation of the desired streamflow index (e.g., annual streamflow, low-flow index, flood quantile, etc.) in the space of catchment descriptors. The second technique, named Topological kriging or Top-kriging, predicts the variable of interest along river networks taking both the area and nested nature of catchments into account. PSBI and Top-kriging are applied for the regionalization of Q355 (i.e., a low-flow index that indicates the streamflow that is equalled or exceeded 355 days in a year, on average) over a broad geographical region in central Italy, which contains 51 gauged catchments. The two techniques are cross-validated through a leave-one-out procedure at all available gauges and applied to a subregion to produce a continuous estimation of Q355 along the river network extracted from a 90m elevation model. The results of the study show that Top-kriging and PSBI present complementary features. Top-kriging outperforms PSBI at larger river branches while PSBI outperforms Top-kriging for headwater catchments. Overall, they have comparable performances (Nash-Sutcliffe efficiencies in cross-validation of 0.89 and 0.83, respectively). Both techniques provide plausible and accurate predictions of Q355 in ungauged basins and represent promising opportunities for regionalization of low-flows.

Highlights

Hydrological predictions generally have to deal with the inadequacy or deficiency of observations for the site of interest
The analysis enables us to assess the performances of Topkriging and Physiographical-Space Based Interpolation (PSBI) and to compare advantages and disadvantages associated with the application of each methodology, gaining additional insights on the applicability and usefulness of the two spatial interpolation techniques for the prediction of streamflow indices in the context of the Prediction in Ungauged Basins (PUB) initiative
The coordi- We assessed the reliability of the techniques and the unnates were identified from the set of nine geomorphoclimatic certainty of the associated predictions of Q355 in ungauged descriptors illustrated in Table 1 by performing a Principal basins by applying a leave-one-out cross-validation proce

Summary

Introduction

Hydrological predictions generally have to deal with the inadequacy or deficiency of observations for the site of interest (see the decade on Prediction in Ungauged Basins promoted by the International Association of Hydrological Sciences – IAHS; Sivapalan et al, 2003). The regionalization of the low-flow regime is a central topic in this research area (see e.g., Smakthin, 2001; Castellarin et al, 2004; Laaha and Bloschl, 2006a; Castiglioni et al, 2009), as it can be conveniently applied to surface water assessment in ungauged basins. The scientific literature reports a number of regionalization studies in which the availability of surface water and other hydrological attributes can be evaluated at a given ungauged site on the basis of the data collected at basins that are hydrologically similar to the site of interest (see e.g., Vogel and Kroll, 1992; Ludwig and Tasker, 1993; Furey et al, 2000; Brath et al, 2002; Brath et al, 2003).

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Conclusion