| Urban drainage infrastructure is very important for urban flood control and disaster reduction.Its design and planning standards mainly depend on the traditional precipitation frequency analysis.In the traditional precipitation frequency analysis,the precipitation series need to meet the stationary assumption,that is,the precipitation series are independent and identically distributed.However,the stationary hypothesis is challenged by the impact of global climate change and human activities,and the traditional precipitation frequency analysis method is not applicable.The design results obtained by continuing to use the traditional methods will increase the project operation risk or increase the unnecessary project cost.Under the changing environment,it is necessary to analyze the nonstationary frequency of precipitation series.In the analysis of nonstationary precipitation frequency,the method of constructing time-varying probability distribution model based on time-varying moment method is the most widely used.This method assumes that the statistical parameters of the probability distribution obeyed by the precipitation series will change with time or other physical covariates,which leads to the probability distribution obeyed by the precipitation series will change every year,and the return period is no longer a one-to-one correspondence with the design value.Therefore,in the changing environment,it is very important to predict the probability distribution change of extreme precipitation in the future and estimate the nonstationary design precipitation in line with the engineering practice.This paper constructs a time-varying probability distribution model based on the time-varying moment method,and deduces the change of probability distribution of extreme precipitation in the future by predicting covariates.The average value method of design years that can consider the design life of the project is used to estimate the nonstationary design precipitation.Firstly,based on different sampling methods,different trend test methods are used to analyze the trend of daily and hourly extreme precipitation in Beijing-Tianjin-Hebei region.Then,for the precipitation series with significant trend changes,a nonstationary model is constructed with time and physical factors as covariates,and the change of future extreme precipitation subject to probability distribution is predicted by predicting covariates.The average value method of design years is used to estimate the nonstationary design precipitation.A consistent model is constructed for the precipitation series without significant trend change,and the traditional method is used to estimate the design precipitation.Finally,combined with the consistent and nonstationary design results,the updated spatial distribution of future design precipitation in Beijing-Tianjin-Hebei region under changing environment and the revised precipitation intensity-duration-frequency curve are obtained.The main conclusions of this thesis are as follows:(1)Different extreme precipitation indices are used to reflect the trend of daily extreme precipitation in Beijing-Tianjin-Hebei region.Under different trend test methods,the daily precipitation intensity of most stations in Beijing-Tianjin-Hebei region shows a significant or insignificant upward trend.The days of extreme precipitation at all stations showed a significant or insignificant downward trend.The extreme precipitation contribution rate,heavy precipitation and annual maximum daily precipitation of most stations show a significant or insignificant downward trend.The number of stations with an upward or downward trend of extreme precipitation threshold is roughly the same.In addition,none of the extreme precipitation indicators have completely consistent results under different trend test methods,but the differences of different methods are about three stations.The precipitation series are obtained by peak-over threshold and annual maximum sampling,and the trend of hourly extreme precipitation in Handan area is analyzed.The main performance is that the long-duration precipitation shows a downward trend,and the trend changes gradually increase with the short-duration.(2)Under the changing environment,for the two extreme precipitation indices of annual maximum daily precipitation and heavy precipitation volume,which show a significant change trend in Beijing-Tianjin-Hebei region,the effect of the nonstationary model is better than that of the stationary model.It confirms the results of trend analysis and shows that extreme precipitation does show nonstationary characteristics.After updating the spatial distribution of design precipitation in Beijing-Tianjin-Hebei region under the changing environment,the spatial distribution of the design values of the two extreme precipitation indices of annual maximum daily precipitation and heavy precipitation volume in Beijing-Tianjin-Hebei region in the next 50 years is high in the southeast and low in the northwest,and the high design values are mainly concentrated in the east,central and southern regions.Compared with the spatial distribution of design precipitation in Beijing-Tianjin-Hebei region under the nonstationary method,the stationary method will overestimate the design precipitation in the east and south of Beijing-Tianjin-Hebei region.Therefore,continuing to use the design results under the stationary method is bound to increase the unnecessary project cost,while the spatial distribution of design precipitation in Beijing-Tianjin-Hebei region under the nonstationary method is in line with the trend of extreme precipitation.(3)For the hourly scale extreme precipitation with significant trend change in Handan area,the nonstationary model has better effect and can better describe the nonstationary of extreme precipitation than the nonstationary model with time as covariate and physical factors as covariate.For short-duration(1-18 hour)extreme precipitation,regional process(urbanization factor)is the best covariate.For longduration(24-48 hour)extreme precipitation,the global process(ENSO)is the best covariate.Under the changing environment,the urbanization factor characterized by land use is taken as the covariate,and the probability distribution change of extreme precipitation in the future is deduced by predicting urbanization.The revised precipitation intensity-duration-frequency curve considering the impact of urbanization conforms to the trend change of extreme precipitation.(4)The design life average method solves the estimation problem of nonstationary design precipitation from the perspective of reliability,which has a theoretical basis.Moreover,this method can consider the design life of the project,and the estimated design value in the design life of the project is consistent with the trend change of precipitation series.It has a good application prospect. |
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