基于均一化资料的西安极端气温变化特征研究

基于1960~2015年西安气象站点逐日最高温、最低温数据,采用RHtest软件对非均一化气温序列进行订正,进而选取16项极端气温指数,对西安极端气温变化特征进行分析。结果表明：① 由于气象站点迁移,西安气温资料存在非均一性,导致极端气温变化趋势被低估;② 全球变暖背景下,西安极端气温变化表现出：“快速增温与平稳波动并存,冷暖变化趋势相反,夜晚增暖趋势比白天明显,白天波动变化明显于夜晚,持续性高温事件变化不大,持续性低温事件大幅下降”的变化特征;③ 通过不同区域趋势变化对比、冷暖、昼夜变化关系对比发现,受城市热岛影响,西安极端低温事件减少更为突出,远高于中国其他对比区域（秦岭南北、黄土高原、东北地区等）;④ 在昼夜变化上,西安极端气温变化与中国、全球变化具有一致性,但是通过冷暖指标对比发现,西安极端气温变化具有区域性,表现为冷昼日数下降高于暖昼日数上升,冷夜日数下降高于暖夜日数上升,冷持续日数和暖持续日数共同表现为下降趋势。

Changes of Extreme Temperature Events in Xi’an City Based on Homogenized Data

Based on daily maximum and minimum temperatures observed by the China Meteorological Administration at the Xi’an meteorological station during the period 1960-2015, the series exhibiting breakpoints are adjusted using RH test software. Temporal trends of 16 extreme temperature indices are evaluated by least-squares linear regression and moving average methods; the linear trends are significant for 11 of these 16 indices. The trends of extreme temperature indices for Xi’an, China, the globe, and other regions in China are compared. Further, trends of the relative magnitudes of cold versus warm indices and day versus night indices are compared. The results are as follows: 1) Due to the migration of the meteorological station, the value of the temperature series is lower than the original meteorological station data. The warming trends of extreme temperatures are underestimated based on the in-homogeneity dataset. 2) In the context of global warming, extreme temperature variation presents its own characteristics in Xi’an. First, the extreme temperature trends show rapid warming with stable fluctuation, but the opposite trends occur in warm and cold indices; warm indices increase while cold indices decrease. Second, the warming trends are faster during the nighttime than the daytime, whereas the amplitudes of fluctuations are greater during the daytime than the nighttime. Third, warm spell events increase slowly, but cold spell events decrease rapidly. 3) Extreme temperature indices are compared between Xi’an and other regions (the southern and northern regions of the Qinling Mountains, the Loess Plateau, northeast China, etc.). Due to the impact of the urban heat island phenomenon, the decrease of extreme low temperature events is more pronounced in Xi’an than in the other regions compared. 4) With regard to daytime versus nighttime indices, the nighttime indices in all regions show the characteristic of warming faster than the daytime indices. In the case of cold versus warm indices, Xi’an exhibits its regional features: the warming magnitude is faster on cold days than on warm days, and a similar trend is seen on cold nights and warm nights; indices of cold and warm spell durations show a downward trend. Overall, this study indicates that the trends of temperature extremes in Xi’an are in accordance with global warming during 1960-2015.