IntroductionFloods, droughts, and heavy storms are some of the manifestations of environmental events that cause tremendous destruction and bring misery to human existence. Flooding can bring havoc to property, infrastructure, animals, plants, and human lives. Floods have been a major challenge in Pakistan for many years. The main reason for these floods is extreme monsoon rainfall due to the unusual climate-change-led seasonal cycle of land temperature in Pakistan that has made the monsoon rainfall more severe and produced a large volume of water in the northern mountainous region of the country. Summer monsoon in the subcontinent is going to be extreme. Temperature, CO 2 , and CH 4 records of past decades represent this change [1]. The monsoon in Pakistan starts in early July and remains until the end of September. Besides human loss, the financial loss in the last six decades is estimated at $37.554 billion US.In construction of flood protection projects, information on flood magnitude and their frequencies is critical [2]. Frequency analysis is the estimation of how often a specified event will happen. The main objective of FFA is to relate the magnitude of extreme events to their frequency of happening through the use of probability distributions [3].This study is interesting in two aspects, first by selecting a robust estimation method and second by selecting a best distribution for at-site FFA using AMSF data in the country using different goodness fit tests. The first aspect is a prerequisite for the second, in the sense that we need estiPol. J. Environ. Stud. Vol. 24, No. 6 (2015), [2345][2346][2347][2348][2349][2350][2351][2352][2353]
AbstractOur paper compares the L-moments (MLM), TL-moments (MTLM), and maximum likelihood estimation (MLE) methods in order to select the best-fit distribution of annual maximum stream flow (AMSF) data for at-site flood frequency analysis (FFA) in Pakistan. Initially this study considered different probability distributions. Best distribution for each site is identified using different goodness of fit tests such as mean absolute deviation index (MADI), Anderson darling (AD) test, probability plot correlation coefficient (PPCC), and L-moments ratio diagram. Results show that GPA distribution is the most suitable distribution for most of the sites, followed by GLO and GEV distributions, respectively. MLM is found to be the most suitable estimation method in finding the best-fit distribution for most of the sites in this study, followed by MTLM and MLE. For at-site FFA we also estimated different return periods associated with given flood magnitudes (quantiles of best fit distribution/maximum annual discharge values). It is found that estimated flows based on fitted distribution are in close agreement with observed flows.