中文摘要：

客观分析强降水事件的发生频率及其致灾因子危险性，能为局地洪涝灾害的防灾、减灾规划及灾害预警提供科学依据。探讨了基于二元Copula函数的强降水致灾变量联合分布及其在强降水危险性分析中的应用。利用北京地区2005—2014年逐时降水资料提取强降水事件案例，通过建立能反映两个主要致灾因素——降水持续时间和过程降水量依存关系的二元联合分布模型，计算了北京地区强降水事件条件重现期，并以此为基础开展危险性分析。研究表明，北京地区强降水事件的持续时间多小于24h，且主要服从广义极值和对数正态分布，而过程降水量则更适用于广义极值分布；通过GumbelCop—ula函数能较好刻画过程降水量与持续时间的相互依存关系。北京地区短时强降水重现期受持续时间影响明显，仅基于降水量的重现期估算会低估其致灾危险性，利用基于Copula函数的条件重现期能更合理描述不同强降水情景致灾因子的危险性特征及其空间差异性特征。北京地区持续时间小于12h、过程降水量在50mm以上的强降水事件多呈东北一西南走向，而持续时间在6h以内的50mm以上强降水则在北京城区及东北部地区更加频繁。

英文摘要：

The objective analysis of the frequency and risk of heavy rainfall can provide scientific basis for disaster prevention and mitigation planning and disaster warning. In this study, the Copula methodology is applied to establish a bivariate Copula distribution model for heavy rainfall variables, i.e. the duration and accumulated precipitation, based on hourly rainfall data collected at 18 rain-gauge stations in Beijing during the period from 2005 to 2014. The conditional return period is then calculat- ed and the risk of heavy rainfall is analyzed. These analyses demonstrate that the duration of heavy rainfall is less than 24 h in Beijing, which mainly follows the generalized extreme value （GEV） or logarithmic normal （LN） distributions, while accumula- ted precipitation is fitted to the GEV distribution in most stations. The Gumbel Copula is identified to be appropriate for descri- bing the relationship between rainfall duration and accumulated precipitation for most gauges. The return period of short-dura- tion rainfall is significantly influenced by the factor of duration in Beijing, which will result in the underestimation of heavy rainfall risk when only the factor of precipitation is considered. However, it is found that the conditional return period based on the bivariate Copula can comprehensively describe the property of heavy rainfall frequency and corresponding hazard risk. The heavy rainfall events with a duration less than 12 h and an accumulated precipitation of more than 50 mm often occur in an area extending from the northeast to southwest of Beijing, while the heavy rainfall events with duration less than 6 h and an accumu- lated precipitation of more than 50 mm occur more frequently in urban area and the northeastern area of Beijing.