西北地区东部气候的转折性变化

The Transitional Change of Climate in the East of Northwest China

过去半个世纪,西北地区东部经历了暖干化趋势,21世纪以来,这种趋势是继续维持还是发生了变化?针对这个问题,本文基于最新资料对西北地区东部的降水和平均温度的变化特征进行再分析,结果表明,对于降水而言,近58年来西北地区东部仍呈减少趋势,但21世纪初以来却呈显著增加趋势,特别是近8年的增加幅度更大。对于平均温度而言,近58年来整个西北地区东部仍呈显著的变暖趋势,但是36°N以南和以北区域变化特征并不完全一致,21世纪初以来,36°N以北地区由于出现了阶段性变冷,使得变暖特征明显减缓,而36°N以南地区虽然继续呈现变暖特征,但变暖幅度同样明显减缓。因此自21世纪初以来西北地区东部的降水和平均温度发生了转折性变化。初步分析发现这种降水增多、增温减缓甚至阶段性变冷的转折性变化可能与PDO从暖位相转换为冷位相有关。

In the past half century,the eastern of Northwest China has experienced a warm and dry trend.In this century,this trend is to continue to maintain or change?For this issue,based on the latest observations from the National Meteorological Information Center,the variations of annual precipitation and mean temperature in the eastern of Northwest China were reanalyzed using some statistical methods.From the long-term trend,the winter precipitation in the eastern of Northwestern region is weakly increasing,and there is no obvious trend in summer,but the spring and autumn are decreasing.So it is the decreasing trend of spring and autumn that makes the annual precipitation decrease.Although the changes in precipitation in the year and the four seasons are not completely consistent,they have shown an increasing trend in the past 20 years since the beginning of this century,especially since 2010,the precipitation is more obvious.For the average temperature,the eastern of Northwestern region shows a significant warming trend,and it is more significant in the 1990 s.In addition,the characteristics of the south and north regions of 36°N are not completely consistent.Since the beginning of this century,the region north of 36°N has shown a stage of cooling,while the area south of 36°N continues to show warming,but the warming rate is obviously slowed down.In terms of seasons,the average temperature of the four seasons in eastern of Northwestern has increased in the past 58 years.Compared with the south of the region from the mid-1980 s to the end of the 1990 s,the temperature increase in the north of 36°N is greater than south of 36°N.In the north of 36°N,the warming rate in the spring and summer of the first 10 years of this century has slowed down noticeably.Autumn and winter temperature has shown a stage of cooling,and the same as annual temperature.In the south of 36°N,the spring,summer and autumn have not shown obvious cooling in the past century,but they showed a stage of cooling in the late 1990 s.The staged cooling makes the annual average temperature have no obvious change trend in the first 10 years of this century.In addition,whether it is north or south of 36°N,the temperature increase characteristic of the average temperature has changed from the beginning of this century,the temperature increase has slowed down,and even the stage has become cold.Therefore,the annual precipitation and average temperature in the eastern of Northwest China have undergone a turning point since the beginning of this century.Preliminary analysis found that this transitional change with increased precipitation,slower temperature increase and even phased cooling may be related to the conversion of PDO from warm phase to cold phase.