西北地区气候湿化趋势的新特征

New characteristics about the climate humidification trend in Northwest China

21世纪初有研究提出西北气候暖湿化,但由于当时变湿时段短、变幅小,对此观点有不少存疑,并且对暖湿化的趋势发展、持续时间及影响程度等问题缺乏明确结论.本研究通过构建变湿综合指数,利用多元数据,系统分析了西北暖湿化的时空特征.研究表明,在百年尺度上,西北西部和东部温度均经历了20世纪40年代和60年代至今的两个增暖期,且当前的暖期更强;西部与东部的降水在很多时期呈跷跷板变化,但21世纪开始西部与东部同时进入增湿期.1961年以来西北西部基本为一致变湿趋势,1987年以来更为显著;而东部在1961~1997年呈干化趋势,1997年也转为湿化趋势.西部的温度、降水和干燥度变化一致性较好,大多时段以冷干和暖湿为主;而东部变化的一致性较差,21世纪之前很少出现暖湿时段,直至21世纪暖湿配置才较为频繁.西北地区温度呈现空间一致的增加特征,且变暖程度逐渐增强;降水则呈西增东减的空间变化,但西增东减的分界线近3个气候态时段以来持续东扩.西北地区降水、干燥度和变湿综合指数均表现为非线性增强,变湿的增强、东扩征兆显著,21世纪以来尤为突出.不过,当前气候暖湿化并没有改变基本的气候形态,但如果未来气候趋势持续当前的增强特征,对基本气候形态的改变并非没有可能.气候变湿的增强、东扩特征可能是21世纪以来西风环流和东亚夏季风环流协同增强作用的结果.

At the beginning of 21st century,a study suggested that Northwest China’s climate is becoming warmer and more humid.However,there were doubts about this conclusion because the humidification changes on a small scale only last for a short period,and also suspicions about the development,duration,and impact of the warming-wetting trend in this region.This paper sets out several factors,such as the area,intensity of humidification,and comprehensiveness of the wetness index,to characterize the wetting degree.Furthermore,by using measured climate data,CRU data,climate scenario predictions,and ecological and hydrological data,we systematically analyze temporal and spatial evolution of the warming-wetting trend in Northwest China.Studies have shown that Northwest China has experienced two warming periods during the last century,i.e.,the 1940s,and the period from the 1960s to the present(the current warming period).The latter is more substantial.The precipitation in the west and east part of Northwest China has a seesaw change process in many periods.However,humidification has simultaneously occurred in both regions since the beginning of this century.The current precipitation in the west part of Northwest China has far exceeded any period over the past 100 a.In contrast,the east part’s recent rainfall is still currently lower than that of the 1950s and 1960s.Since 1961,Northwest China’s west region has experienced consistent humidification,which has been more pronounced since 1987.Simultaneously,the east part was drying from 1961 to 1997,and has become humid since 1997.The temperature,precipitation,and aridity index changes in the west part show the same patterns.In most periods,the west part was either cold-dry or warm-wet.In comparison,such consistency of the temperature,precipitation,and aridity changes does not exist in the east region.Before this century,warm-wet climates rarely occurred in the east region,having become more frequent.This is probably due to the different dominant temperatures and precipitation processes in the west and east regions.From a spatial point of view,the temperature increases in the whole of Northwest China,and the precipitation increases in the west region and decreases in the east region.The area with increasing rainfall has become larger during the past three climatic periods,and currently covers the whole of Northwest China.The precipitation,aridity index,and comprehensive humidity index in Northwest China have a non-linear increasing trend.The expanding humidity trend has been significant since the beginning of this century.The current warming and humidification have not changed the basic climate pattern in Northwest China.However,if the current trend continues,they would change the climate pattern in the future.Such climate change may result from the simultaneous enhancement of the westerly circulation and the East Asian summer monsoon circulations in this century.The climate warming and humidification in Northwest China significantly impacted extreme weather events,water resources,ecological environment,and agriculture during this century.This research will provide a basis for decisionmaking on issues such as implementing the Western development strategy in the new era,the ecological protection and high-quality development of the Yellow River Basin,environmental construction planning,and water resources management policies in Northwest China.