Comparative assessment of predictions in ungauged basins – Part 2: Flood and low flow studies

Abstract

Abstract. The objective of this paper is to assess the performance of methods that predict low flows and flood runoff in ungauged catchments. The aim is to learn from the similarities and differences between catchments in different places, and to interpret the differences in performance in terms of the underlying climate-landscape controls. The assessment is performed at two levels. The Level 1 assessment is a metaanalysis of 14 low flow prediction studies reported in the literature involving 3112 catchments, and 20 flood prediction studies involving 3023 catchments. The Level 2 assessment consists of a more focused and detailed analysis of individual basins from selected studies from Level 1 in terms of how the leave-one-out cross-validation performance depends on climate and catchment characteristics as well as on the regionalisation method. The results indicate that both flood and low flow predictions in ungauged catchments tend to be less accurate in arid than in humid climates and more accurate in large than in small catchments. There is also a tendency towards a somewhat lower performance of regressions than other methods in those studies that apply different methods in the same region, while geostatistical methods tend to perform better than other methods. Of the various flood regionalisation approaches, index methods show significantly lower performance in arid catchments than regression methods or geostatistical methods. For low flow regionalisation, regional regressions are generally better than global regressions.

Regional parent flood frequency distributions in Europe – Part 2: Climate and scale controls

“…One visible consequence of the higher dispersion and skewness of the flood frequency distributions with decreasing catchment area and increasing aridity is the fact that predicting flood magnitudes and exceedance probabilities in ungauged basins is more difficult in smaller, more arid catchments, as compared to bigger, less arid ones (see e.g. Salinas et al, 2013). Therefore, the main findings from the analysis presented in the previous sections need to be interpreted in a hydrological…”

Estimation of flood warning runoff thresholds in ungauged basins with asymmetric error functions

“…Among the possible approaches (statistical and process based) to predict floods in ungauged basins, many researchers have traditionally applied regression-like regionalisation methods for (i) the estimation of the index flood (Darlymple, 1960), usually defined as either the mean or the median (that is the 2-year return period quantile) of the annual maximum flood series, or for (ii) the direct estimate of other quantiles of annual maxima in ungauged basins (Stedinger and Lu, 1995;Salinas et al, 2013). Such methods are based on the assumption that there is a relationship between catchment properties and the flood frequency statistics and are implemented through a regression-type model that relates the flood quantile or the index flood to a number of relevant morpho-climatic indexes.…”

Regional parent flood frequency distributions in Europe – Part 1: Is the GEV model suitable as a pan-European parent?

“…Marchi et al, 2010;Gaume et al, 2010). It is therefore important that effective and practical procedures are available, to assist hydrologists in making inferences about flood risk, both at gauged and at ungauged sites Salinas et al, 2013).…”