Comparing Spatial Interpolation Schemes for Constructing a Flow Duration Curve in an Ungauged Basin

This study aims to investigate the applicability of proposed ensemble interpolation technique based on both geographical and physiographical spaces, for prediction of flow duration curve (FDC) at ungauged site. The interpolation schemes were applied for selected 15 different percentiles of the FDC. Firstly, different FDC parametric models were tested to approximate FDCs at gauged sites. It was found that the suggested reliable ensemble averaging (REA) model outperformed the traditional deterministic models (linear, exponential, and logarithmic models). The REA model approximated the FDC with high consistency and small deviations from the observed percentiles. The results obtained by the REA model were further utilized to define homogeneity in the selected region. Secondly, based on the inverse distance weighting (IDW) concept, both geographical and physiographical spaces estimations were ensemble (using proposed estimated true value (ETV) method) to predict the hydrological information (FDC) at ungauged sites. It was noted that ETV based interpolation provided more efficient, reliable and consistent efficiency. Finally, to identify physical conditions that could favor the high predictability of the proposed methodology, we investigated the relationship between Nash-Sutcliffe efficiency (NASH) and catchments attributes. The results indicated that significance correlations were observed between NASH and catchments attributes even though no clear tends exist.