基于SPEI的云南中部区域干旱时空变化特征分析

利用云南中部地区1961~2010年逐月降水和气温资料,采用降水距平百分率和历史旱情资料验证了标准化降水蒸散指数(Standardized Precipitation Evapotranspiration Index,SPEI)在该地区的适用性,并采用Mann-kendall突变检验、Morlet小波和经验正交函数(Empirical Orthogonal Function,EOF)等方法,分析了该地区干旱的时空演变特征,结果表明:(1)SPEI与降水距平百分率在时空上具有很好的相关性,验证了SPEI对降水变化的敏感性;(2)SPEI指数与历史旱情资料比较吻合,能够有效地反映云南中部区域的干旱特征;(3)年均SPEI呈波动下降趋势,干季SPEI降低趋势明显。年均SPEI存在着24a的主周期和9a的次周期,并于1977年发生了突变,此后开始降低,在整体上呈现出干旱化的趋势;(4)从SPEI的空间分布特征来看,其在整体上受大尺度气候系统的影响表现出一致的下降趋势,而在区域内部则表现出东南-西北(干热河谷)的反向结构差异。

TEMPORAL AND SPATIAL VARIATION OF DROUGHTS OVER THE CENTRAL YUNNAN PLATEAU BASED ON SPEI

Based on the monthly data of 37 meteorological stations over the Central Yunnan Plateau during 1961-2010, the standardized precipitation evapotranspiration index (SPEI) was used to study the spatiotemporal patterns of droughts. To assess the temporal patterns of droughts as multi-scale events, the SPEI were calculated for seasonal (6 months) and annual droughts (12 months). In this study, the trends of SPEI were detected with linear regression and Mann-Kendall nonparametric test. The morlet wavelet analysis method was used to detect the change interval of annual mean SPEI. The spatial distribution characteristics of SPEI were analyzed via empirical orthogonal function (EOF). The results indicated that: (1) the annual mean SPEI at 37 meteorological stations of the Central Yunnan Plateau was positively correlated with precipitation anomaly percentage and had good sensitivity to the variation of precipitation. Spatial patterns of the SPEI in 2010, 2005 and 1993 over the Central Yunnan Plateau showed good coincidence with the historical drought records; (2) over the Central Yunnan Plateau, annual mean SPEI showed a decreasing trend since the beginning of the 1970s, however an increasing trend was found in the middle of 1990s, and then a continuous decreasing after 2000. The SPEI at 6-month timescale shows a significant decreasing trend in the dry-season (November-April in the following year) in the whole, but there was no significant trend in the rainy season (May-October); (3) the morlet wavelet analysis revealed that the annual mean SPEI fluctuated significantly with the interval of 24 years and 9 years. The Central Yunnan Plateau tends to be dryer after an abrupt changes in annual mean SPEI occur in 1977; (4) from the spatial distribution, four spatial patterns of SPEI variability were objectively defined by the EOF analysis, which were associated with distinct temporal variations and geographical area over the Central Yunnan Plateau. As a result of the influence of large scale climate systems, the annual mean SPEI showed a decreasing trend in the whole research area. Most significant decreasing rate of annual mean SPEI was found in the Southeast parts of the study region. There was no significant trend of annual mean SPEI in the Southwest, whereas the hot-dry valleys along the Jinsha River showed a significant increasing trend of annual mean SPEI during the past five decades.