长江三峡库区大雾的变化特征分析及原因初探

Preliminary Assessment on Changes of Fog in the Region around Three Gorges Reservoir after Water Pounding

利用近54年三峡库区6个气象站的逐日雾、相对湿度和能见度的历史资料,对1954年以来三峡库区雾的气候变化特征,尤其是近几年三峡水库蓄水以后大雾的变化及其产生变化的可能原因进行了讨论。结果表明:1954～2007年三峡库区雾日数呈弱的增加趋势,而2000年后库区的雾日明显减少。相对湿度与雾日数之间存在显著的正相关关系,而相对湿度与气温呈明显的负相关关系。气温变化影响相对湿度变化,从而影响雾的发生频率是三峡库区雾变化的重要原因。2000年以后,在全球变暖大背景及城市化的共同影响下,三峡库区气温显著升高,相对湿度明显减小,是导致雾日大幅减少的直接影响因素。另外,分析还显示,无论是雾日数还是相对湿度都表现出了明显的年代际振荡特征,2000年后三峡库区相对湿度减小进而雾日减少正是受到了这种年代际背景的影响。就目前的观测表明,三峡水库蓄水的小气候效应影响小或还没有明确显现。

Climatic variation characteristics of fog days in the region around the Three Gorges Reservoir since 1954,especially the changes after water pounding in 2003,are analyzed based on the daily observation dataset of fog days,relative humidity,and visibility at the six stations around the Three Gorges Reservoir. It is found that the numbers of fog days show a weak increasing trend from 1954 to 2007,while they had a significant decreasing trend after water pounding in 2003. The possible reason for the obvious decrease of fog days after water pounding is discussed. The mean temperature has significant negative correlation with relative humidity,and strong positive correlation with the number of fog days in the region around the Three Gorges Reservoir. It＇s the important factor of fog variation in the region aroud the Three Gorges Reservoir that the temperature change has an impact on relative humity,and affects the frequency of fog further. The mean temperature has increased greatly since the 1990s,and the relative humidity as well as the fog frequncy has decreased obviously since the 2000s in the region around the Three Gorges Reservoir. These changes result from both the climate warming and the urbanization. Additionally,analyse shows that both the number of fog days and relative humidity have obvious and similar interdecadal oscillations,with relative high values from the 1960s to the 1970s and in the early 21st century but low from the 1980s to the 1990s. This significant interdecadal oscillation affected the decrease of relative humidity and then fog days after water pounding,as the years after 2003 belong to the downward phase of the interdecadal oscillation. The comparison analysis shows that the local effect of the water pounding is limited,with the climatic background being dominant.