西南地区夏季降水量的多尺度变化特征
Multi-Scale Variation Characteristics of Summer Precipitation in Southwest China

为了更好地分析中国西南地区近60年来夏季降水的变化特征，利用1961~2017年西南地区76个气象站点的降水量资料和NCEP/NCAR再分析月平均资料，主要运用经验正交函数分解(EOF)、Morlet小波分析、集合经验模态分解(EEMD)等方法对该地区近60年夏季降水量的空间分布特征以及时间变化特征进行研究。结果表明：1) 西南地区近60年来夏季降水量空间分布不均匀，大体呈现东多西少，南多北少的变化趋势。2) EOF分析表明：第1模态显示西南地区夏季降水呈全区一致型；第2模态显示夏季降水在西北–东南有“正–负–正”的分布类型；第3模态显示夏季降水呈全区一致型。3) 小波分析表明：夏季降水主要有2年、3~7年、8年以及12~22年的变化周期。4) EEMD分解表明：夏季降水具有2.85年、6年、16.28年、28.5年的变化周期，且在整个时间尺度上呈下降趋势。5) 西南地区趋势系数正值区和负值区交错分布，年平均降水的相对变率不大，从西南到东北由正转负。
In order to better analyze the variation characteristics of summer precipitation in Southwest China over the past 60 years, the precipitation data of 76 meteorological stations and NCEP/NCAR reanalysis monthly mean data during 1961~2017 were used. Empirical orthogonal function decomposition (EOF), Morlet wavelet analysis, Ensemble Empirical Mode Decomposition (EEMD) and other methods were used to study the spatial distribution characteristics and temporal variation characteristics of summer precipitation in this region in recent 60 years. The results show that: 1) The spatial distribution of summer precipitation in southwest China in recent 60 years is not uniform, showing a general trend of more precipitation in the east and less precipitation in the west, more precipitation in the south and less precipitation in the north. 2) EOF analysis shows that the first mode shows that the summer precipitation in Southwest China is consistent throughout the whole region. The second mode shows a “positive-negative-positive” distribution pattern of summer precipitation in northwest and southeast China. The third mode shows that the summer precipitation is consistent in the whole region. 3) Wavelet analysis shows that summer precipitation had a period of two years, three to seven years, eight years and twelve to twenty-two years. 4) EEMD decomposition showed that summer precipitation had a period of 2.85 years, 6 years, 16.28 years and 28.5 years, and showed a decreasing trend in the whole time scale. 5) The positive and negative trend coefficients are interleaved in southwest China, and the relative variability of annual mean precipitation is not large, which turns from positive to negative from southwest to northeast China.