采用基于相对湿润度的干旱指数分析方法和黄土高原19612010年气候要素资料, 研究了黄土高原春季干旱时空变化、异常分布和次区域演变特征.结果表明: 19612010年黄土高原春季干旱强度变化呈现明显中心区域强、周边区域弱的分布特征, 其中中部腹地干旱强度增加趋势倾向率最大, 中部周边干旱强度增加次之, 东北部和西部边缘呈减弱趋势.研究区不同区域春季干旱强度呈同位相变化是干旱变化的首要空间分布模态, 异常中心区域在陕北、陇东及宁夏西南部.东西部反相位分布模态反映了黄土高原东西部所受大气系统影响差异性的特征.根据载荷向量不同模态空间异常分布型, 可将春季干旱划分为西北部型、东北部型和南部型等3个次区域异常型, 南部春季干旱强度时间序列呈显著增强趋势, 其由弱变强的突变点出现在1977年, 西北部和东北部干旱强度也呈波动增强趋势, 但未通过显著性检验, 没有突变.西北部和南部春季干旱指数存在显著的3~4年振荡周期, 东北部存在显著的5～6年振荡周期.
Drought index analytical method which was based on relative moisture index was used to study the temporal and spatial variation, abnormal distribution and sub-regional evolution characteristic of spring drought on Loess Plateau, according to meteorological data between 1961 and 2010. The results showed that, the intensity variation of spring drought on Loess Plateau from 1960 to 2010 had an obvious distribution characteristic that intensity is higher in central area and lower in surrounding area. Among which the increase of drought intensity in hinterland of central area has the highest rate of tendency, and then in rest places of central area. West and northeast region of the plateau have an attenuate tendency. The main spatial distribution mode of drought variation is the phase variation for spring drought, central abnormal areas located in north Shaanxi, east Gansu and southwest Ningxia. Secondly, opposed phase distribution model in east and west areas provide a reflection of characteristics of differences between east and west region of Loess Plateau, which was caused by the influence of atmosphere system. According to spatial abnormal distribution of different loading vectors and modes, spring drought can be divided into three sub-regional abnormal distributions, e.g. northwest kind, northeast kind and south kind. The intensity of spring drought in south sub-region has a significant increasing tendency, the mutation point of which from weak to strong appeared in 1977, drought intensity in northwest and northeast regions also showed a fluctuated increasing tendency, but no mutation was emerged since the fluctuation failed to pass the significance test. The index of spring drought in northwest and south regions has an obvious high frequency fluctuating period of 3~4 years, while northeast part has an obvious high frequency fluctuating period of 5~6 years.
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