Change Characteristics of Precipitation in Northwest China from 1961 to 2018
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摘要: 邻接青藏高原地区的中国西北地区是最大的欧亚干旱区,其降水变化对全球变化的响应和对干旱环境及其青藏高原气候变化都具有特殊的指示意义。基于1961~2018年中国西北地区144个站的逐日降水、逐月气温观测资料,分析了西北地区的降水变化特征及趋势。结果表明:(1)近60年以来,西北地区92%站点的年降水量呈现增加的趋势,只有甘肃东南部不到10%的站点呈下降趋势;(2)季节尺度上,春、夏、秋季中超过75%站点的降水呈现增加的趋势,但最显著的是,几乎所有站点在冬季的降水为增加趋势,秋、冬季降水的增加相对较少,反映了冬季风对西北地区降水影响的特点;(3)进入21世纪以来,西北地区夏季和年降水量仍然维持准3 a周期特征,春、秋季的周期具有阶段性、冬季降水量具有较稳定的约3 a周期,因此,自然周期变化对降水增加的贡献并不大。西北地区降水量在过去60年来确实呈现出增加趋势,尤其21世纪以来降水量持续增加,但增加的量是有限的,不足以改变其干旱半干旱的气候特征。Abstract: The Northwest China, which is adjacent to the Qinghai-Tibet Plateau, is the largest Eurasian arid region. Its precipitation responses to the global climate changes, to the arid environment, and to the climate change in the Qinghai-Tibet Plateau region are special significance. Based on the observational data of the daily precipitations and monthly temperatures at 144 stations in Northwest China from 1961 to 2018, the characteristics and trends of the precipitation change in Northwest China are analyzed. The results showed that: (1) During nearly the last 60 years, 92% of the stations in Northwest China observed an increasing trend of annual precipitations, while less than 10% of the stations in southeastern Gansu observed a decreasing trend. (2) On the seasonal scale, precipitations at more than 75% stations showed an increasing trend in spring, summer, and autumn, however the most significant is that almost all the stations had an increasing trend of precipitations in winter. The increase of precipitations in autumn and winter was relatively small, which reflected the influence of winter wind on the precipitation in Northwest China. (3) Another feature is that since the beginning of the 21st century, the summer and annual precipitations in Northwest China have maintained a quasi-3 a cycle. The spring and autumn cycles have several stages, while the winter precipitation has a relatively stable cycle of nearly 3 a. Therefore, natural cycle changes do not contribute much to the increase of the precipitation. The precipitation in Northwest China has indeed increased over the past 60 years, especially since the beginning of 21st century when the precipitation has been continuously increasing. However, the increased precipitation amount is limited, which is not enough to change the arid and semi-arid climate characteristics in the region.
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图 1 1961~2017年西北地区(a)春季、(b)夏季、(c)秋季、(d)冬季、(e)年降水量[绿(红)色箭头表示降水趋势增加(减少)]、气温(圆圈,单位:°C a−1)的变化趋势和降水量标准差(等值线,单位:mm)。N表示站点数,黑色加号表示降水量趋势通过95%信度水平的显著性检验,所有站点的气温变化趋势均通过95%信度水平的显著性检验。图e中虚线框表示标准差较大的两个区域A、B
Figure 1. The change trends of (a) spring, (b) summer, (c) autumn, (d) winter, (e) annual precipitation [the green (red) triangles represent the increasing (decreasing)] and temperature (circles, units: °C a−1), and precipitation standard deviation (contour lines, units: mm) in Northwest China from 1961 to 2017. N represent station numbers, the black plus signs indicate that the precipitation change trends pass the test at 95% confidence level, temperature change trends at all stations pass 95% confidence level. In Fig. e, the dashed boxes represent areas A and B with large standard deviations
图 2 1961~2018年区域(a)A、(b)B月降水量(黑色柱状,单位:mm)、月降水量标准差(灰色柱状,单位:mm)、月平均气温(折线,单位:°C)
Figure 2. Monthly precipitation (black bars, units: mm), standard deviation (gray bars, units: mm) of monthly precipitation, and monthly mean temperature (fold lines, units: °C) averaged in regions (a) A and (b) B from 1961 to 2018
图 3 1961~2017年西北地区(a)春季、(b)夏季、(c)秋季、(d)冬季、(e)年降水量第一特征向量场(LV1),右上角数值表示LV1的方差贡献率
Figure 3. The first eigenvector fields (LV1) of (a) spring, (b) summer, (c) autumn, (d) winter, (e) annual precipitation in Northwest China from 1961 to 2017, numbers at top right corner indicate the variance contribution rate of LV1
图 4 1961~2017年西北地区(a)春季、(b)夏季、(c)秋季、(d)冬季、(e)年降水量第二特征向量场(LV2),右上角数值表示LV2的方差贡献率
Figure 4. The second eigenvector fields (LV2) of (a) spring, (b) summer, (c) autumn, (d) winter, (e) annual precipitation in Northwest China from 1961 to 2017, numbers at top right corner indicate the variance contribution rate of LV2
图 5 1961~2017年西北地区(a)春季、(b)夏季、(c)秋季、(d)冬季、(e)年降水量第一特征向量场的时间系数(PC1),红(蓝)色柱状代表正(负)值,虚线代表9年滑动平均,右下角数值表示LV1的方差贡献率
Figure 5. The time coefficients (PC1) of the first eigenvector fields of (a) spring, (b) summer, (c) autumn, (d) winter, (e) annual precipitation in Northwest China from 1961 to 2017. The red (blue) bars represent the positive (negative) values of the time coefficient, the dashed lines represent the 9-year moving average, numbers at bottom right corner indicate the variance contribution rate of LV1
图 6 1961~2017年西北地区(a)春季、(b)夏季、(c)秋季、(d)冬季、(e)年降水量第二特征向量场的时间系数(PC2),红(蓝)色代表正(负)值,虚线代表9年滑动平均,右下角数值表示LV2的方差贡献率
Figure 6. The time coefficients (PC2) of the second eigenvector fields of (a) spring, (b) summer, (c) autumn, (d) winter, (e) annual precipitation in Northwest China from 1961 to 2017. The red (blue) bars represents the positive (negative) values of the time coefficient, the dashed lines represent the 9-year moving average, numbers at bottom right corner indicate the variance contribution rate of LV2
图 7 1961~2018年西北地区(a)春季、(b)夏季、(c)秋季、(d)冬季降水量变化(柱状)与趋势(实线),季节平均最高(Tmax)、最低气温(Tmin),季节平均最高与最低气温差值的趋势(虚线),(e)年降水量
Figure 7. (a) Spring, (b) summer, (c) autumn, (d) winter precipitation (bars) and trend (solid line), the highest (Tmax) and lowest (Tmin) average seasonal temperatures, the trend of the average seasonal difference between the highest and lowest temperatures (dashed lines), (e) annual precipitation in Northwest China from 1961 to 2018
图 8 1961~2017年西北地区(a)春季、(b)夏季、(c)秋季、(d)冬季、(e)年降水量的小波系数。实(虚)线代表正(负)值,阴影区域表示周期通过90%信度水平的显著性检验
Figure 8. Wavelet coefficients of (a) spring, (b) summer, (c) autumn, (d) winter, (e) annual precipitation in Northwest China from 1961 to 2017. The solid (dashed) lines represent positive (negative) values, the shaded areas represent periods pass the test at 90% confidence level
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