Abstract Flood flows at the sites of a homogeneous region usually have significant cross-correlations. The effect of intersite correlation on the sampling variance of regional growth factors is studied. An analytical expression is derived for the asymptotic sampling variance of the regional average coefficient of variation for multivariate normal floods. The results for the variance of flood quantiles are checked by simulation. For other two-parameter distributions such as the Gumbel, Weibull and gamma, a simulation study is performed to obtain the sampling variances of regional growth factors.