近50年中国地面气候变化基本特征

CLIMATE CHANGES OF CHINA′S MAINLAND OVER THE PAST HALF CENTURY

采用国家基准气候站和基本气象站的地面资料,系统地分析了中国大陆地区1951年以来近地表主要气候要素演化的时间和空间特征。结果表明,中国近50 a来年平均地表气温变暖幅度约为1.1℃,增温速率接近0.22℃/(10 a),比全球或半球同期平均增温速率明显偏高。地表气温增暖主要发生在最近的20余年,其季节和空间特征与前人分析结论基本一致。降水量变化趋势对所取时间段和区域范围敏感。1951年以来全国平均降水量变化趋势不明显,但1956年以来略有增加。降水变化的空间特征明显而相对稳定,东北北部、包括长江中下游的东南部地区和西部广大地区降水增加,而华北地区以及东北东南部和西北东部地区降水明显减少。分析还发现,近50a来全国平均的日照时数、平均风速、水面蒸发等气候要素均呈显著下降趋势,但积雪地带的最大积雪深度却有所增加。中国日照时间和水面蒸发量变化的空间特征很相似,减少最明显的地区均发生在华北和华东,新疆次之。影响中国年代以上尺度气候变化的因子错综复杂,人类活动引起的大气中温室气体浓度增高可能在一定程度上影响了中国近50 a来的气候,但考虑到尚存的不确定性,目前仍不能给出明确结论。中国东部大部分地区日照时间和水面蒸发量减少可能均起源于人为排放的气溶胶影响,平均风速减弱也有利于水面蒸发量下降,而在西部地区云量和降水量的变化可能更重要。

A data set of mean temperature, precipitation and other climate parameters for 740 stations across China＇s Mainland was used to analyze climate change in China's Mainland. The data set has been processed more carefully, and the main in-homogeneities existing in the monthly mean temperature data have been checked and corrected. The widely accepted procedures for creating area-averaged climatic time series and for calculating linear trend have been used. Analyses have been made for annual and monthly mean temperature, precipitation, pan evaporation, sunshine duration, wind speed, and the maximum depth of snow cover. The analyses show that annual mean surface air temperature in China＇s Mainland as a whole rose by about 1.1 ℃ for the last 50 years, with a warming rate of about 0.22℃/10 a. The warming in the later half 20th century is more rapid than the average values of the world and the Northern Hemisphere. The most evident warming occurred in winter and spring as expected. Northeast China, North China and Northwest China experienced more significant warming in terms of annual mean temperature, while a cooling trend reported in earlier studies is still continuing. Summer mean temperature in the middle and lower reaches of the Yangtze River also decreased in the last 50 years. No significant long-term change in the country-averaged annual precipitation was seen for both the past 50 years. However, an obvious tendency of drying in the Yellow River Basin and the North China Plain in terms of precipitation has been found, and the largest drop in precipitation occurred in Shandong Province. Meanwhile, an insignificant wetting trend in the Yangtze River Basin and most parts of western China could be detectable. For the Yangtze River Basin, the increased annual precipitation mainly resulted from the significant rising of summer rainfall, though winter precipitation also tended to increase. Since 1956, the country-averaged pan evaporation has had a significant trend to decrease, with a changing rate of - 34.5 mm/10a. The most significant decrease occurred in spring and summer in the North China Plain and the lower reach of the Yangtze River. The largest decrease in Pan-evaporation in terms of absolute values is in northwestern China. It is worth to note that average sunshine duration and wind speed are also experiencing a tremendous drop in most regions of the country during the past 50 years, and they usually bear a similarity with pan evaporation in spatial pattern of the tendencies. In parts of the North China Plain, annual sunshine duration in the recent years is almost 500 hours fewer than that of 50 years ago. We have also tentatively analyzed the possible causes for the observed changes. However, it is be premature at this moment to give a definite conclusion.