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

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 semiarid 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.