Assessment of Outdoor Thermal Comfort in a Hot Summer Region of Europe

Heat waves are increasingly frequent in Europe, especially in South European countries during the summer season. The intensity and frequency of these heat waves have increased significantly in recent years. Spain, as one of the southern European countries most affected by these recurring heat waves, particularly experiences this phenomenon in touristic cities such as Cordoba. The aim of this study was to perform an experimental assessment of outdoor thermal comfort in a typical three-hour tourist walkable path of the historical center of Cordoba. The experimental study was carried out in the three-hour period of higher temperatures from 16:30 to 19:30 h CEST (UTC+2) on a normal summer day (6 July 2023), a day with a heat wave (28 June 2023) and a day with a higher heat intensity, called a super heat wave (10 August 2023). Environmental conditions such as a radiant temperature, ambient temperature, wet bulb temperature, air velocity and relative humidity were measured at three different heights corresponding to 0.1 (ankles), 0.7 (abdomen) and 1.7 (head) m. The results show extremely high levels of heat stress in all bioclimatic indices throughout the route. Cumulative heat stress ranged from “very hot” conditions at the beginning of the route to becoming “highly sweltering” at the end of the route. The average temperature excess over the thermal comfort threshold was very high and increased with the heat intensity. In addition, a correlation analysis was carried out between the bioclimatic indices studied, with the UTCI index standing out for its strong correlation with other thermal comfort indices. The findings emphasize the need for interventions to improve the urban environment and promote better outdoor thermal comfort for city dwellers through measures such as green infrastructure, UHI mitigation and increasing public awareness.

欧洲热浪愈发频发，夏季在南欧国家尤为突出。近年来，此类热浪的强度与频次均显著提升。西班牙作为受周期性热浪影响最严重的南欧国家之一，其旅游城市科尔多瓦（Cordoba）更是这一现象的典型受影响区域。

本研究旨在对科尔多瓦历史中心一段典型的3小时游客步行路径开展户外热舒适度实验评估。实验选取了三个典型夏日：普通夏日（2023年7月6日）、热浪日（2023年6月28日）以及超强热浪日（2023年8月10日，当日热强度更高），在每日气温最高的3小时时段——中欧夏令时（CEST，UTC+2）16:30至19:30——开展数据采集。

本研究测量了0.1m（脚踝高度）、0.7m（腹部高度）及1.7m（头部高度）三个不同高度处的环境参数，包括辐射温度、环境温度、湿球温度、空气流速与相对湿度。

结果显示，整条步行路径的所有生物气候指数均呈现极高的热应激水平。累积热应激程度从路径起始处的“极热”状态逐步升级至终点处的“极度闷热”状态。相较于热舒适度阈值的平均温度超标幅度极高，且随热强度提升而进一步增大。

此外，本研究还对所涉及的生物气候指数开展了相关性分析，其中通用热气候指数（UTCI）与其他热舒适度指数的相关性最为显著。

研究结果强调，亟需通过绿色基础设施建设、城市热岛效应（UHI）缓解措施以及提升公众认知等手段，优化城市环境，改善城市居民的户外热舒适度。