Abstract:

Based on the data of pentad precipitation from the main stations in Ningxia during 1961 － 2010，the relations between summer precipitation concentration degree ( PCD) ，precipitation concentration period ( PCP) and Z － index are studied． The results show that PCP appeared in 4 － 5 pentad of July，and the PCD was decreased from north to south area in Ningxia． The temporal variability of maximum precipitation in the north region of Ningxia was more bigger，and extreme precipitation occurred more in the north area than that in the central and southern area of Ningxia． The PCD and PCP presented slight decreasing trend from 1961 to 2010 on the whole， but PCD increased and the variability of PCP increased in recent 10 years． There was a good positive correlation between the PCD and PCP，when PCP appeared later，the PCD was more concentrative． The Z － index from the 1960s to 1980s changed more in Ningxia， and its variability decreased obviously since the middle of the 1980s． There was a close relation between the summer drought and PCD，when precipitation was more concentrative，the possibility of floods was more，and when the PCD was small，drought occurred easily． The position of west Pacific subtropical high had some influence on flood or drought from July to August in Ningxia，the subtropical high was near to north in drought years and near to south in flood years．

Key words: Ningxia, summer, precipitation － concentration degree, drought /flood

摘要：

利用宁夏主要气象台站1961 ～ 2010 年逐侯降水量序列资料，研究了表征降水量时间分配特征的降水集中度( PCD) 、集中期( PCP) 与表征旱涝程度的Z 指数之间的关系，结果表明: 宁夏夏季各地降水PCP 基本出现在7 月4 ～ 5 候，PCD 空间分布特征明显，自北向南逐渐减小，北部一年中最大降水出现的时间变率大，且出现极端降水的可能性比中南部要大; 近50 a 全区夏季PCD 与PCP 整体呈微弱的下降趋势，但2000 年代增大，PCP 变幅加大; 夏季PCP 和PCD 显著正相关，PCP 出现得越晚，PCD 集中度越高; 宁夏夏季干旱Z 指数在1960 年代到1980 年代中期变幅较大，易出现大旱大涝，1980 年代中期以后变幅明显减小，尤其是1980 年代中后期以及1997 年以后的绝大部分年份为正常;夏季降水PCD 对干旱有显著的影响，降水PCD 高，雨涝发生的概率越大，降水集中度低，干旱发生的概率大; 主汛期7 ～ 8 月副高的位置对宁夏旱涝有一定影响，偏旱年份副高易偏南，偏涝年份易偏北。

关键词: 宁夏, 夏季, 降水集中程度, 旱涝