以UTCI探討臺灣氣候變遷之研究

Abstract

近年來全球氣候變遷導致高溫事件發生頻率與持續時間增加，使戶外熱舒適環境逐漸惡化。相較於僅以氣溫評估熱環境，通用熱氣候指數（Universal Thermal Climate Index, UTCI）能整合氣溫、相對濕度、風速及平均輻射溫度等氣象因子，更能反映人體實際熱感受。本研究以UTCI為評估指標，利用中央氣象署16個代表性測站2004年至2024年逐時氣象資料，計算各測站UTCI，並採用臺灣在地化UTCI熱舒適分級，分析不同地區戶外熱舒適長期變化趨勢，探討都市、沿海及山區熱環境差異，以及氣候變遷對人體熱暴露之影響。 研究結果顯示，全臺16個測站皆呈現一致的季節循環，UTCI於7至8月達全年最高，冬季最低。2021至2024年間所有測站平均UTCI皆高於2004至2020年，增幅介於0.59～1.60°C，其中以新竹增加最多（+1.60°C），竹子湖、宜蘭、基隆及日月潭亦增加超過1.3°C。都市及西部平原地區熱壓力最為明顯，臺中、臺南、高雄及臺北近年平均UTCI分別為27.25°C、26.52°C、25.77°C及25.51°C，夏季日間UTCI多超過40°C，最高可達50°C以上，且夜間UTCI仍維持28～31°C，顯示都市熱島效應使夜間散熱能力下降。沿海地區因海洋調節作用，全年UTCI變化幅度較小；高山測站則全年UTCI最低，其中阿里山近年平均僅13.71°C，夏季多維持舒適至輕微熱壓力，仍具良好避暑效果。 過熱與過冷時數分析顯示，16個測站皆呈現過熱時數增加及過冷時數減少之共同趨勢，其中大型都市全天過熱時數約增加30～50小時/10年，中小城市增加15～40小時/10年，反映近年人體熱暴露時間持續延長。 綜合而言，臺灣UTCI空間分布主要受都市化程度、海拔高度及海洋調節共同影響。研究結果證實氣候變遷已使臺灣戶外熱舒適環境逐漸惡化，尤其都市地區熱暴露風險持續增加。本研究可提供未來都市熱環境改善、熱風險管理、氣候調適規劃及公共健康政策之參考依據，並作為建築氣候與都市設計之應用基礎。

In recent years, climate change has increased the frequency and duration of extreme heat events, resulting in the gradual deterioration of outdoor thermal comfort. Compared with using air temperature alone to evaluate thermal conditions, the Universal Thermal Climate Index (UTCI) integrates multiple meteorological variables, including air temperature, relative humidity, wind speed, and mean radiant temperature, thereby providing a more comprehensive assessment of human thermal perception. This study employed UTCI as the primary thermal comfort indicator and calculated hourly UTCI values using meteorological data collected from 16 representative weather stations of the Central Weather Administration (CWA) in Taiwan from 2004 to 2024. A Taiwan-localized UTCI thermal comfort classification was adopted to investigate the long-term variations in outdoor thermal comfort across different regions and to evaluate the impacts of climate change on human heat exposure in urban, coastal, and mountainous environments. The results indicate that all 16 stations exhibited a consistent seasonal cycle, with UTCI reaching its annual maximum during July and August and its minimum in winter. The average UTCI for the period 2021–2024 was higher than that for 2004–2020 at all stations, with increases ranging from 0.59 to 1.60°C. Hsinchu showed the greatest increase (+1.60°C), while Zhuzihu, Yilan, Keelung, and Sun Moon Lake each recorded increases exceeding 1.3°C. Urban areas and the western plains experienced the most pronounced heat stress. The recent average UTCI values in Taichung, Tainan, Kaohsiung, and Taipei were 27.25°C, 26.52°C, 25.77°C, and 25.51°C, respectively. During summer daytime, UTCI frequently exceeded 40°C and occasionally surpassed 50°C, while nighttime UTCI remained between 28 and 31°C, indicating that the urban heat island effect has reduced nocturnal cooling capacity. In contrast, coastal regions exhibited relatively stable annual UTCI variations due to the moderating influence of the ocean. Mountainous stations recorded the lowest UTCI values throughout the year. Alishan, for example, had a recent average UTCI of only 13.71°C and generally remained within the comfortable to slightly warm categories during summer, demonstrating its continued suitability as a summer retreat. The analysis of heat and cold exposure hours revealed a common trend of increasing heat exposure and decreasing cold exposure across all 16 stations. The annual duration of overheating increased by approximately 30–50 hours per decade in major metropolitan areas and by 15–40 hours per decade in medium-sized cities, indicating that the duration of human heat exposure has continued to increase in recent years. Overall, the spatial distribution of UTCI in Taiwan is primarily influenced by the degree of urbanization, elevation, and maritime effects. The findings confirm that climate change has progressively degraded outdoor thermal comfort in Taiwan, particularly by increasing heat exposure risks in urban areas. The results of this study provide a scientific basis for improving urban thermal environments, heat risk management, climate change adaptation planning, and public health policies, and may also serve as a reference for applications in building climatology and urban design.