Pleasant outdoor thermal conditions depend on a wide range of climatic elements. The impact of rainfall events, as important climatic elements, on providing thermal comfort, has been less explored in the available literature. The work presented herein investigates the impact of Rainy Days as well as a Day Prior to (Dprior) and a Day Post rain (Dpost) events on thermal conditions in the southern coastal region of the Caspian Sea. In this study, rainfall events during 1961-2017 observational period were categorized based on their intensity. Then, human thermal comfort during non-rainy (sunny) and rainy days was estimated and compared by using the radiation-driven Physiological Equivalent Temperature (PET) index, Universal Thermal Climate Index (UTCI) and Perceived Temperature (PT) index. Furthermore, difference between the average of thermal conditions in rainy days compared to a day prior and a day post rain events was calculated separately for comfort, cold and heat stress thresholds of each bioclimatic index. Finally, the correlation between the average of indices for rainy days and the frequency of rainfall events of each specific year was computed. Results suggested that overall average of studied indices for all rainy days is lower than the average for days prior and post the rain events. PET index has shown to be most impacted and reduced as a result of rain events and therefore more indicative of a cool ing effect. The observed difference in total average of PET in rainy days compared to non-rainy days were 8.30 °C, 5.86 °C and 8.85 °C for Babolsar, Rahst and Gorgan stations, respectively. Generally, the cooling effect of rain events on the temperature for a day prior rain events is higher than a day post rainfall. Finally, the trend analysis on rainy days in the studied period revealed that the average of bioclimatic indices in western stations (Babolsar and Rasht) are increasing whereas a decreasing trend was observed for Gorgan as more of an eastern station.

中文翻译：

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量化降雨事件对里海南部沿海站室外热舒适性的冷却效应

宜人的室外热条件取决于各种气候因素。降雨事件作为重要的气候因素对提供热舒适性的影响在现有文献中鲜有探讨。本文介绍的工作调查了下雨天以及前一天 (Dprior) 和后一天雨 (Dpost) 事件对里海南部沿海地区热条件的影响。本研究根据强度对 1961-2017 年观测期的降雨事件进行了分类。然后，通过使用辐射驱动的生理等效温度（PET）指数、通用热气候指数（UTCI）和感知温度（PT）指数来估计和比较非雨天（晴天）和雨天的人体热舒适度。此外，对于每个生物气候指数的舒适度、寒冷和热应力阈值，分别计算了雨天与雨前一天和雨后一天的平均热条件之间的差异。最后，计算了雨天指数平均值与特定年份降雨事件频率之间的相关性。结果表明，所有雨天研究指数的总体平均值低于降雨事件前后几天的平均值。PET 指数已显示受降雨事件影响最大且降低，因此更能表明冷却效果。对于 Babolsar、Rahst 和 Gorgan 站，在雨天与非雨天相比，观察到的 PET 总平均值的差异分别为 8.30 °C、5.86 °C 和 8.85 °C。一般来说，降雨事件对降雨事件前一天温度的冷却效果高于降雨后一天。最后，研究期间雨天的趋势分析表明，西部站点（Babolsar 和 Rasht）的生物气候指数平均值正在增加，而 Gorgan 则更多地是东部站点，观察到下降趋势。