Influence de la taille des regions homogenes sur la qualite de l'ajustement des crues de rivieres non jaugees du Quebec Influence of the Size of Homogeneous Regions on the Goodness of Fit of Ungauged River Floods in Quebec

摘要

The influence of the size of homogeneous regions on the goodness of fit of ungauged river floods is studied by cross validation. Two initial regions, one homogeneous and the other potentially homogeneous, formed by 38 and 34 rivers were used. Homogeneous sub-regions of various sizes were randomly created to study the behaviour of the non-selected rivers, considered as ungauged for the purpose of this study. Results have shown that the size of the sub-regions has less impact on the χ~2 test results than the inherent quality of each river. In fact, the size of the sub-regions was inversely proportional to the variability, which means that a region of small size has a larger chance to lead to realisation exceeding the χ~2 test critical value than a region of large size. In spite of this finding, the influence of the size of the regions was small if one considers that for the worst case scenario (homogeneous sub-regions of five rivers), the percentage of failure of the χ~2 test was increased by only about 3%. However, the distribution of the regional L-moment ratios decreases with the size of the sub-regions. The selection of larger homogeneous regions thus allows a reduction in the variability of the estimation of regional T-year events.