西北地区5—9月极端干期长度异常的气候特征

Climatic Characteristics of Extreme Drought Period from May to September in Northwest China

利用西北地区107个测站1960-2004年逐日降水资料,统计5-9月连续无雨日数（日降水量小于0.1mm）,得到西北地区5-9月的逐年极端干期长度,在此基础上分析了极端干期长度的基本时空分布特征;对资料标准化后进行经验正交展开（EOF）和旋转经验正交展开（REOF）,研究其异常的空间结构及时间演变规律;并利用小波分析方法,分析了极端干期的周期性及突变的时间。结果表明：西北地区极端干期长度的气候平均分布与海拔高度及地理位置有较大的关系。西北地区极端干期长度异常在空间上主要表现为整体一致型,其次表现为东西相反的变化趋势。旋转载荷向量场（RLV）反映出极端干期长度的5个异常气候区：高原东北区,南疆区,青海区,北疆区和西北东南区。5个异常区极端干期长度均存在较明显的2-3 a高频振荡;其次西北东南区存在明显的16 a低频变化周期,而其他各区存在明显的8-11 a低频变化周期。新疆及青藏高原20世纪80年代后极端干期有缩短之趋势。高原东北区,青海区,北疆区的极端干期长度的分布有两个突变点;南疆区、西北东南区则各有一突变点。

Using the daily precipitation data（ 1960-2004）of 107 meteorological stations, and the methods of EOF, REOF and wavelet analysis, we analyzed the basic temporal-spatial distributions of extreme drought period and its cycles and abrupt time in Northwest China. The results show that there are close relationships between average distribution of extreme drought period and altitude, geographical location. The first load vector of extreme drought pe- riod variations has the characteristic of spatial consistency, and the second has adverse variation trend in east and west part. The rotated load vectors reflect 5 anomaly climatic areas of extreme drought period： northeast of Tibet Plateau, southern Xinjiang, Qinghai, northern Xinjiang and southeast of Northwest China. There is obvious 2-3 years high frequency cycle of extreme drought period in the 5 areas, 16 a and 8-11 a low frequency cycle in southeast of Northwest China and the other 4 areas, respectively. The extreme drought period has been shorting in Xinjiang and Tibet Plateau since 1980s. The distribution of extreme drought period has two abrupt points in northeast of Tibet Plateau, Qinghai and northern Xinjiang, whereas one abrupt point in southern Xinjiang and southeast of Northwest China.