上海近30年来蒸发变化及其城郊差异分析

Variation of Evaporation and Evaporation Differences Between Proper and Suburb in Shanghai in Recent 30 Years

统计分析了上海龙华中心气象站和周边9个郊区气象站1970～2000年蒸发资料,结果表明:(1)近30年来,上海郊区的蒸发变化和气候的冷暖期变化基本一致,20世纪80年代郊区蒸发量总体明显低于70年代;进入90年代增暖期后,郊区蒸发量呈逐渐上升趋势。(2)市区蒸发状况与郊区出现明显反差,20世纪80年代市区蒸发量高于70年代,90年代以后市区蒸发量总体明显下降,与郊县蒸发量变化趋势相背离。(3)城郊蒸发量历史资料系列的配对样本T检验表明,近30年来上海地区的蒸发存在明显的城郊差异,城郊蒸发的差异及变化与区域下垫面状况关系密切。

Based on the observed data of evaporation from 1970-2000 of 10 meteorological stations, in Shanghai proper and its suburbs, by means of some statistical methods, including cumulative anomaly percentage, 5-year running average, t-test for paired samples etc., the spacial and temporal features of evaporation in Shanghai are discussed in this paper. The results obtained are as follows: (1) The climate in Shanghai has significantly changed into the warm type since the year of 1987. In this study, the variation of evaporation in Shanghai suburbs basically accords with the climate change in recent 30 years. Compared with the 1970s, the annual evaporation of the 1980s has generally decreased in Shanghai suburbs. During the 1990s, the annual evaporation of suburbs has increased along with the rising of the air temperature. The trend of cumulative evaporation anomaly percentage for suburbs resembles the figure of sine wave basically during the studied period from 1970 to 2000. (2) On the contrary, the annual evaporation trend for the Shanghai proper is obviously opposite with the trend of suburbs in studied period. Compared with the 1970s, the annual evaporation of the 1980s has increased in Shanghai proper. Although the regional air temperature and precipitation in Shanghai had both increased in the 1990s, the evaporation of Shanghai proper had reversely showed a trend of greatly reducing. The trend for time series of cumulative evaporation anomaly percentage for proper from 1970 to 2000 resembles the figure of cosine wave, which deviates with the trend of suburbs. (3) Evaporation differences between Shanghai proper and suburbs are obvious with 2-tailed sig. value being less than 0.01. The regional distribution of evaporation nearly correlates with differences of regional ground states. Baoshan and Chongmin are located in the estuary of Yangtze River in northeast Shanghai, so the evaporation of the two districts is more than that of the other suburbs due to the high wind speed. It is worth discussing that the results in this paper are based on the observed data, but the processes and mechanisms of evaporation differences between Shanghai proper and suburbs should be further researched though a series of experiments. Otherwise, because the evaporation data for a relative long period are different to obtain from different type of observation instruments (Eφ20 and E601), it is difficult to analyze the long variable cycle of evaporation.