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www.hydrol-earth-syst-sci-discuss.net/6/6691/2009/
doi:10.5194/hessd-6-6691-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
Flood trends and variability in the Mekong river
German Research Centre for Geosciences, Section 5.4, Hydrology, Potsdam, Germany
Abstract. Annual maximum discharge is analyzed in the Mekong river in Southeast Asia with regard to average flood trends and 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 general 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 general extreme value function with linearly varying scale and location parameter. NSGEV outperforms MK and OLS, both because it incurred 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
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 average flood trend and to have a more complete view of the changes. Overall, results showed an increasing likelihood of extreme floods during the last half of the century, although the probability of an average flood decreased during the same period. The variance, estimated with the wavelet power spectrum as a function of time, allowed to identify a period of enhanced variance in the last quarter of the 20th century, which confirmed the results of the NSGEV.
We conclude that the initial absence of detected positive trends in the hydrological time series was a methodological misconception due to over-simplistic models.
Discussion Paper (PDF, 3020 KB) Interactive Discussion (Closed, 6 Comments) Final Revised Paper (HESS)
Citation: Delgado, J. M., Apel, H., and Merz, B.: Flood trends and variability in the Mekong river, Hydrol. Earth Syst. Sci. Discuss., 6, 6691-6719, doi:10.5194/hessd-6-6691-2009, 2009. Bibtex EndNote Reference Manager XML
