中国西北干旱区降水时空分布特征

Spatio-temporal change of precipitation in arid region of the Northwest China

利用中国西北干旱区122个气象站点1961—2011年月降水量资料,运用线性趋势、Mann-Kendall非参数趋势和突变检验法、Morlet小波分析等方法研究了西北干旱区降水量空间分布及多时间尺度下的变化规律和趋势。结果表明:近50年来西北干旱区降水量呈增加趋势,95.9%的站点有增湿特征,全区增湿趋势为9.31mm/10a(P<0.01),但增湿幅度存在区域差异性,其中祁连山亚区(38.67mm/10a)增湿最明显;从季节来看,冬季增湿具有全区普遍性,但夏季增湿的区域差异性特征明显。全区及各亚区降水量在20世纪80年代至90年代初有明显的突变特征,除内蒙西部亚区外均通过了0.01的显著性水平检验,降水量序列存在4、8、12a和22a振荡周期,其中22a尺度振荡周期最强,其次是12a尺度。全区32%的年份降水量属正常范围,偏干年份为24%,异常偏干年份为12%,异常偏湿和偏湿年份均为16%。20世纪70年代之前降水量略低于标准降水均值,80年代开始有区域性增湿趋势,90年代之后全区增湿均较明显,正距平年数比例由70年代的10%上升至21世纪初的80%,西北干旱区整体处于相对湿润时段,且增湿趋势明显。

Using monthly precipitation records from 122 meteorological stations in the arid region of Northwest China, the spatial and temporal distribution of precipitation were analyzed for the period 1961--2011. The Mann-Kendall trend test and Morlet wavelet analysis were utilized to detect the spatio-temporal distribution of the mean annual and seasonal precipitation. In the present paper, the Northwest arid area was divided into the northern Xinjiang region, the southern Xinjiang region, Qilian Mountains, Tianshan Mountains, Hexi Corridor region, and the Inner Mongolia Plateau region. The results obtained indicate that the mean annual precipitation （MAP） in the northwest arid region had a significant rising trend （P 〈 0.01 ）, at a rate of 9.31 mm/decade. The mean annual precipitation in the Qilian Mountains area rose the fastest, increasing by 38.67 mm/decade; the second fastest was on the Tianshan Mountains, increasing by 16.79 mm/decade; the slowest increase was in the Hexi Corridor, southern Xinjiang, and western Inner Mongolia, increasing by 8.49 mrn/deeade, 5.44 mrnfdecade, and 5.09 mm/deeade, respectively. The Mann-Kendall test showed that the increasing trend of the mean annual precipitation in each area was statistically significant at P〈0.05 level, except in western Inner Mongolia. A rising tendency of the mean annual precipitation was observed in 95.9% of the stations in the study region, but the amplitude shows regional differences. The Tianshan Mountains, Qilian Mountains, and northern Xinjiang show a rising tendency in all stations, followed by those in southern Xinjiang and the Hexi Corridor, whereas the lowest increase is in western Inner Mongolia, accounting for 77.78% of the stations. Centers of the highest increase in mean annual precipitation were identified, for example, Yeniugou （52.5 ram/decade） in the Qilian Mountains, Tianchi （22.8 mm/decade） in the middle of the Tianshan Mountains, and Xinyuan （28.3 mm/decade ） west of the Tianshan Mountains. There are seasonal differences in the rising trend of the mean annual precipitation. The rate of precipitation increased the fastest in spring, by 3.32 mm/decade, followed by the rate in summer and winter, by 5.44 mm/decade and 5.09 mm/decade, respectively, whereas it is the slowest in fall （only 2.07 mm/decade）. The precipitation rate in winter was universal across the studied region, it was 98.36% in all stations. Summer precipitation rate presented regional differences; the precipitation rate was 79.51%. Abrupt changes in mean precipitation in the arid region and sub-region of northwest China are evident. The changes occurred in northern and southern Xinjiang and western Inner Mongolia in the middle of the 1980s, in the Hexi Corridor and the Qilian Mountains changes occurred in the middle of the 1970s, and in the Tianshan Mountains the changes occurred in 1991. The abrupt changes in the mean precipitation in each area were statistically significant at P 〈 0.05 level. The Morlet wavelet analysis showed that the precipitation has an approximate 4-year, 8-year, 12-year, and 22-year cycle in the studied region. According to the level of wet and dry, the rates for normal, abnormally dry, dry, wet, and extremely wet mean precipitation series were 32%, 12%, 24%, 16%, increased significantly ; the rate of positive anomalous years it is relatively wetter in the arid region of northwest China, and 16%, respectively. Since the 1980s, precipitation has has increased from 10% in the 1970s to 80% nowadays. Today, with an obvious ongoing increasing trend