Abstract: An accurate description of design rainfalls with different return periods is an important basis for planning and design of water conservancy structures, flood control, and disaster reduction. Based on the hourly rainfall data of 2005 to 2018 from 20 stations in Beijing, this study uses an over-threshold method to extract the depth and duration of heavy rainfalls over different regions, and estimates their joint distribution functions to calculate the design rainfalls of different return periods in each region. The results show that significantly more heavy rainfall events were observed in the downtown of this city than in the mountainous areas; the duration of most rainfalls follows the generalized extreme value (GEV) or Lognormal distributions, while the rainfall depths follow the GEV distribution. The joint distribution of the depth and duration of rainfalls is better characterized using a Gumbel Copula function for most of the regions in the study area, while a Frank Copula function is better in several other regions. The use of binary Copula functions can improve the estimation of design rainfalls of different return periods.

Key words: Beijing, Copula function, rainfall duration, rainfall depth, design rainfall