Regional frequency analysis of annual maximum rainfall in monsoon region of pakistan using L-moments

Abstract

Estimation of magnitude and frequency of extreme rainfall has immense importance to make decisions about hydraulic structures like spillways, dikes and dams etc. This research involves the estimation of regional rainfall quantiles of 23 sites using L-moment based index flood regional frequency analysis. Initially, different tests are applied to check the assumptions of independence, stationarity and identical distribution. An L-moment based discordancy measure is used to detect discordant sites. Since in Pakistan, highly elevated area receive more rainfall. On the basis of this characteristic, the study region is divided into three regions which satisfy the L-moment based heterogeneity statistics using Monte Carlo simulations from Kappa distribution. The regional quantile estimates are obtained from GEV, GNO and GLO distributions which are found to be best choices for all three regions based on L-moment ratio diagram, Z-Statistics and average weighted difference values. For robust regional estimates, some accuracy measures are calculated using a simulation study of regional L-moment algorithm. On the basis of relative bias, relative absolute bias and relative RMSE, GNO is found be best robust for regional quantile estimation at lager return periods of 50, 100, 500 and 1000 and GEV at return periods of 1, 2, 5, 10 and 20 for all three regions.