城市暴雨强度公式复核 −以杭州主城区为例

在气候变化与快速城镇化共同影响下，很多城市暴雨特性发生变化，现行的暴雨强度计算公式可能不再适用，需要复核和更新。以杭州市主城区为例，根据钱塘江江畔闸口站1982—2022年降雨极值资料，分别选用皮尔逊Ⅲ型分布和耿贝尔分布曲线进行线型拟合，采用粒子群优化算法推求暴雨强度公式参数，与现行规范给出的暴雨强度公式进行复核分析。结果表明：在重现期为2~20 a时，根据皮尔逊Ⅲ型分布和耿贝尔分布推求得到暴雨强度新公式的平均绝对均方差均小于0.05mm/min，平均相对均方差均小于5%，符合精度要求；仅当降雨历时为10min时，2个新公式的暴雨强度要小于现行公式的暴雨强度，其他历时下2个新公式的暴雨强度都明显大于现行公式的暴雨强度；经合理性分析，本研究根据最新暴雨资料推求的暴雨强度公式可为杭州市主城区排水防涝工程设计和相关设施建设提供参考。

Revisited urban rainfall intensity formula: An example of the main urban area of Hangzhou

Extreme rainstorms in many cities have broken historical records repeatedly, thus urban flooding disasters occur frequently. Under the background of global warming, extreme rainstorm events showed an increasing trend. In the past few decades, China''s urbanization process advanced rapidly, and the rain island effect caused by rapid urbanization also led to the frequent occurrence of extreme rainstorm events to some extent. The characteristics of many urban rainstorms changed significantly, and the consistency of rainfall series no longer existed, so the current rainfall intensity formula may no longer be applicable. The rainfall intensity formula is one of the basic bases for the construction of urban drainage and waterlogging prevention infrastructure. To objectively reflect the characteristics and rules of urban rainfall and avoid underestimating the intensity of design rainstorms, the current formula needed to be reviewed and updated.The main urban area of Hangzhou was taken as an example, based on the rainfall extreme data from 1982 to 2022 at Zhakou station, the Mann-Kendall trend analysis method and the Pettitt test method were selected to analyze the trend and abrupt change of the annual rainfall extreme and selected Pearson type III distribution and Gumbel distribution curve for model fitting, respectively. The particle swarm optimization algorithm was used for parameter estimation of the rainfall intensity formula, and the newly derived rainfall intensity formulas were reviewed and analyzed. The rationality of the newly derived rainfall intensity formulas was indirectly analyzed using the rainfall extreme data of Gongchenqiao, Zhongcun, and Qibao rainfall stations and the extended historical rainfall extreme data of Zhakou station.The following results were obtained: (a) At the significance level of 0.05, the maximum rainfall series of 10, 20, 30, 45, 90, 360, 540 and 720 min at Zhakou station showed an insignificant downward trend. The annual maximum rainfall series of 60, 120, 180, 240 and 1 440 min showed an insignificant upward trend, and there were no significant abrupt change points in different duration rainfall series. (b) The average absolute mean square deviations of the new rainfall intensity formulas obtained from Pearson type III distribution and Gumbel distribution were less than 0.05 mm/min, and their average relative mean square deviations were less than 5%. (c) The rainfall intensities of the two new formulas were significantly larger than that of the current formula for considering different durations except for the 10-minute duration. (d) Based on the rainfall extreme data of Gongchenqiao, Zhongcun, and Qibao rainfall stations, the design rainfall intensities of the current formula were indirectly verified to be small. (e) It was shown that the difference between the new formulas and the current formula was due to the change in sampling stations and the change in the data years. Trend analysis results of the rainfall series showed that extreme rainfall in the main city of Hangzhou showed an insignificant increase, so the new formulas were more reasonable and safer than the current formula.The rainfall intensity formulas of Pearson type III distribution and Gumbel distribution were deduced and compared with the current formula based on the rainfall extreme data from 1982 to 2022 at Zhakou station. The new rainfall intensity formulas derived from the latest rainstorm data could be used as a reference for the design of drainage and flood prevention projects and the construction of related facilities in the main urban area of Hangzhou.