Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 14 3 2010 10.5194/hess-14-407-2010 http://www.hydrol-earth-syst-sci.net/14/407/2010/ http://www.hydrol-earth-syst-sci.net/14/407/2010/hess-14-407-2010.html http://www.hydrol-earth-syst-sci.net/14/407/2010/hess-14-407-2010.pdf 407 418 2010-03-05 Flood trends and variability in the Mekong river J. M. Delgado jdelgado@gfz-potsdam.de H. Apel B. Merz German Research Centre for Geosciences, Section 5.4, Hydrology, Potsdam, Germany Annual maximum discharge is analyzed in the Mekong river in Southeast Asia with regard to trends in average flood and trends in variability during the 20th century. Data from four gauging stations downstream of Vientiane, Laos, were used, covering two distinct hydrological regions within the Mekong basin. These time series span through over 70 years and are the longest daily discharge time series available in the region. The methods used, Mann Kendal test (MK), ordinary least squares with resampling (OLS) and non-stationary generalized extreme value function (NSGEV), are first tested in a Monte Carlo experiment, in order to evaluate their detection power in presence of changing variance in the time series. The time series are generated using the generalized extreme value function with varying scale and location parameter. NSGEV outperforms MK and OLS, both because it resulted in less type II errors, but also because it allows for a more complete description of the trends, allowing to separate trends in average and in variability.<br> <br> Results from MK, OLS and NSGEV agreed on trends in average flood behaviour. However, the introduction of a time-varying scale parameter in the NSGEV allowed to isolate flood variability from the trend in average flood and to have a more complete view of the changes. 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