近50年来西北半干旱区气候变化特征

Climatic changes of semi-arid region over the northwest China in recent 50a

选用西北半干旱区33个气象站1951-2004年温度、降水、相对湿度、风速、蒸发量等气象观测资料,分析主要气候要素变化规律,揭示了近50年来西北半干旱区气候变化的一些新特征。结果表明,西北半干旱区降水量近50年来年际变化趋势除个别地方外绝大多数地区呈下降趋势,降水量变化曲线线性拟合倾向率在-59.168～-1.143 mm/10 a之间,秋季降水量减少最多,春季次之,而夏季部分地区和冬季大部分地区降水量呈略增趋势。降水量存在3年、6～8年的周期振荡特征,3年周期振荡在1962-1966年为中心的局部时段内最强,之后逐渐减弱。6～8年振荡在1980-1985年为中心的局部时段内最强。气温距平呈上升趋势,气温距平变化曲线线性拟合倾向率在0.074～0.507℃/10 a之间,大部分地区呈先降后升型,转型时间为20世纪60年代后期至70年代前期。冬季气温增高最多,秋季、春季次之,夏季陕、甘、宁交界区及陇中地区气温增高而其余地区气温距平略呈下降趋势。相对湿度近50年来年呈波动变化。平均风速近50年来年际变化趋势除个别地方略增外,其余各地均呈下降趋势。蒸发量近50年来年际变化趋势除个别地方呈上升趋势外,其余各地蒸发量呈下降趋势。

Using 33 stations temperature, precipitation, relative humidity, wind speed, evaporation in the semi-arid region of Northwest China from 1951 to 2004, some new characteristics of climatic changes were posted in virtue of statistics method. The result shows that precipitation displayed a descendant tendency in most areas of the semi- arid region in Northwest China, the tendency rate was -59. 168 - - 1. 143 mm/10a, its maximum descendant tendency was in autumn and the second one in spring, but it displayed an ascendant tendency in some areas in summer and in most areas in winter, 3a and 6 - 8a period was existed, whereas 3a period of oscillation was the strongest, as its centre during the period from 1962 to 1966, and 3a period of oscillation began to weaken from 1966, 6 - 8a period of oscillation was the strongest, as its centre during the period from 1980 to 1985. The temperature showed an ascendant tendency, the tendency rate was 0. 074 -0.507 ℃/10a, it displayed anti-parabola type in most areas, and turning point was from the earlier stage of 1960s to the later stage of 1970s, its ascendant tendency was maximum in winter, the second one in spring and autumn, except for the common boundary of Shaanxi, Gansu and Ningxia Province, which showed a descendant tendency. The precipitation displayed a descendant tendency, whereas the temperature showed an ascendant tendency, which resulted in climate warming and drying in the semi-arid region of Northwest China. The relative humidity showed a wavelike variation. Evaporation also showed an ascendant tendency except for some individual areas in recent 50a.