Comparative study of flood projections under the climate scenarios: links with sampling schemes, probability distribution models, and return level concepts

Abstract

24Traditional stationarity strategy for extrapolating future design floods requires 25 renovation in response to the possible nonstationarity caused by changing climate. 26Capable of tackling such problem, the expected-number-of-events (ENE) method is 27 employed with both Annual Maximum (AM) and Peaks over Threshold (POT) 28 sampling schemes expatiated. The existing paradigms of the ENE method are 29 extended focusing on the over-dispersion emerged in POT arrival rate, for which by 30 virtue of the ability to account, the Negative Binomial (NB) distribution is proposed 31 as an alternative since the common assumption of homogeneous Poisson process 32 would likely be invalid under nonstationarity. Flood return levels are estimated and 33 compared under future climate scenarios (embodied by the two covariates of 34 precipitation and air temperature) using the ENE method for both sampling schemes 35 in the Weihe basin, China. To further understand how flood estimation responds to 36 climate change, a global sensitivity analysis is performed. It is found that design 37 floods dependent on nonstationarity are usually but not necessarily more different 38 from those analyzed by stationarity strategy due to the interaction between air 39 temperature and precipitation. In general, a large decrease in flood projection could be 40 induced under nonstationarity if air temperature presents dramatically increasing trend 41 or reduction occurs in precipitation, and vice versa. AM-based flood projections are 42 mostly smaller than POT estimations (unless a low threshold is assumed) and more 43 sensitive to changing climate. The outcome of the biased flood estimates resulting 44 from an unrestricted use of the Poisson assumption suggests a priority to the NB 45Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016Discuss., doi:10.5194/hess- -619, 2016 Manuscript under review for journal Hydrol. Earth Syst. Sci.