太麻里溪集水區極端水文事件的頻率分析

The frequency analysis is often applied in disaster prevention planning, hydraulic works design, and hazard risk analysis. It is possible to estimate the maximum volumes of intensive rainfall and peak discharge based on a suitable probability distribution. The frequency analysis is also helpful for people to understand the hydrological characteristics in a watershed, and to enhance the efficiency of watershed management. The Taimali stream watershed is selected as a study area in this research. The extreme hydrological events are analyzed including the annual maximum daily discharge and annual one-day maximum rainfall during the period from 1982 to 2009. There are four probability distributions are compared including extreme-value type I distribution, logarithmic normal distribution, Pearson type III distribution, and logarithmic Pearson type III distribution. Moreover, the current trend of climate change is also discussed based on the frequency analysis. Results show that the extremevalue type I distribution is more suitable for the frequency analysis of annual maximum daily discharge. The estimated annual maximum daily discharges in late stage (1996-2009) are higher than that in early stage (1982-1995). Their variation is from 37.93% to 57.88%. The average of annual maximum daily discharges in late stage is bigger surpassing up to 40.63%, and the standard deviation is also exceeding up to 67.94%. In addition, the extreme-value type I distribution and logarithmic normal distribution are more suitable for the frequency analysis of annual oneday maximum rainfall. The estimated one-day maximum rainfalls in late stage are higher than that in early stage. Their variation is from 10.27% to 59.25%. The average of annual one-day maximum rainfall in late stage is bigger surpassing up to 16.09%, and the standard deviation is also exceeding up to 109.30%. In conclusion, there is an increasing trend for the annual maximum daily discharge and annual one-day maximum rainfall in the Taimali stream watershed. The variation is enhancing and the frequency is strengthening. It reveals that the occurrence probability of extreme hydrological events is rising in the further future.