ABSTRACT
Regional frequency analysis (RFA) is proposed in order to estimate the runoff quantiles for ungauged basins. The two main steps of RFA are the homogeneous regions delineation and regional estimation within these regions. (1) The delineation method adopted is agglomerative hierarchical clustering and Ward’s algorithm, using Euclidian distance. The latter assesses the dissimilarity between any two clusters and is calculated between sites in a multidimensional space involving geomorphological and physiographical variables. Furthermore, the region’s homogeneity verification is carried out by silhouette index. (2) The regional estimation was performed using the multivariate copula. The study concerns 22 catchments (areas between 1 km² and 10 km²) situated in Tunisia (from 35°N to 37°N, from 8°E to 11°E), in a semiarid climate zone (average annual rainfall between 280 mm and 500 mm). The delineation was conducted in three homogeneous regions. The correlations are explored between the runoff and rainfall characteristics in each homogeneous region. The found correlation between maximum discharge (Q max ) and average rainfall intensity (I moy ) was significant and pertinent for hydrologic design. The Gumbel copula was adopted for the regions and isolines corresponding to Q max -I moy -Frequency curves were constructed.
