基于标准化降水指数与Z指数的洮河流域干旱趋势分析

Drought Trend Analysis Based on Standardized Precipitation Index and the Z index in the Tao River Basin

采用洮河流域22个站点1951—2010年的逐月降水资料,就标准化降水指数(standardized precipitation index,SPI)与Z指数在流域干旱趋势分析中的应用进行对比研究。结果表明:2种指数在12个月尺度旱情分析方面具有很高的一致性,在单月尺度上,SPI的干旱分析能力较强,对重旱的反映能力优于Z指数。应用SPI指数就洮河流域不同地理—生态区间干旱趋势进行研究,发现冬季是流域干旱的主要分布时段,黄土片区发生干旱的频率和持续的时间均高于青藏片区。1951—2010年,青藏片区总体趋于湿润,黄土片区干旱趋势加重。近30 a,洮河青藏片区西部湿润趋势明显,东南部和下游黄土片区干旱趋势加重。近10 a来,青藏片区东南部旋窝一带干旱范围有所减小,黄土片区中孚一带干旱范围有所扩大。研究结果可为大流域尺度干旱评估提供理论方法借鉴,也可为地方抗旱减灾措施的制定提供数据支撑。

In this study, we used a monthly mean precipitation dataset from 22 gauge station observations since 1951 to 2010 to detect the applicable efficiency by a comparative utilization of the Standardized Precipitation Index and the Z index on regional drought assessment in the Tao River Basin （TRB）. The two indexes featured determi- nable consistency at a time scale of 12-month drought discrimination, while at a time scale of one month, the SPI was more sensitive to reflect the severe drought than the Z index. Then the SPI was used to illustrate drought evolvement in the two eco-geographical zones respectively locating in the eastern Tibetan Plateau （ETP） and south- western Loess Plateau （SLP） , representing very different regional geomorphology and climate, across the TRB. SPI results showed a higher frequency in both regions from November to the following March, although from April to October, the drought occurred seldom, indicating that there would be some consistence of drought occurrence in a year in the ETP and the SLP. Seasonal drought from the end of autumn to the beginning of next spring, especially in the winter, was the dominating drought period in the study area. Statistics also pointed to longer drought with higher frequency of severe ones in the SLP than in the ETP. From 1951 to 2010, the interannual variation of drought in the two regions was different. There has been an overall humidification trend in the ETP while an obvious drought trend in the SLP. Spatially, humidification in the west part of the ETP along with a drought trend in the southeast of that made it a regional heterogeneity of drought evolvement there, while a general drought trend was found in almost the whole SLP during the recent 30 years. In recent 10 years, humidification and acidification in wet and southeast, respectively, in the ETP, have become lightening in both frequency and intensity, while drought occurrence in the SLP kept increasing in both scopes and levels. The research results can provide theory and meth- od reference for large river basin scale drought assessment, and provide data support for the establishment of the lo- cal drought relief measures.