本文采用陇东地区13个气象站的逐日降水和同期NCEP/NCAR再分析资料,基于5个极端降水指数,应用经验正交函数（EOF）、合成分析等方法,研究该地区1967—2015年夏季极端降水的时空特征及极端降水典型年的环流特征。结果表明：（1） 夏季极端降水指数在陇东地区西北部较低,南部和东北部较高,整体呈上升趋势。（2） EOF分析第一特征向量均为正值,第二特征向量则表现为南正北负的反相位分布,在时间系数的极大（小）值年,研究区夏季极端降水在南北方向呈南强（弱）北弱（强）的分布特征最明显。（3） 在强（弱）夏季极端降水典型年,有（无）冷暖空气交汇;上升（下沉）运动增强,向外长波辐射为负（正）异常,对流强（弱）,对应着较多（较少）的降水;水汽通量散度为负（正）异常,有利于（不利于）极端降水发生。

Global climate change accelerates the global and regional hydrological cycle processes, which alter the spatio-temporal distribution of precipitation. Consequently, extreme precipitation events are becoming ever more frequent, which greatly impacts people’s lives. Longdong Region is a semi-arid area with a fragile ecological environment. Therefore, the extreme summer precipitation in this region has a more direct and significant impact on agricultural production, the ecological environment, and people’s lives. We used the daily precipitation data from 13 meteorological stations and NCEP/NCAR reanalysis data in the Longdong Region as the basis for exploring five extreme precipitation indices to explore spatio-temporal characteristics of extreme summer precipitation from 1967 to 2015 and the circulation characteristics of typical years with the help of the empirical orthogonal function (EOF) and composite analysis. The preliminary results showed that the extreme summer precipitation indices are smaller in the Northwest of the Longdong Region than in the south and Northeast, showing an overall upward trend. The EOF eigenvectors of the first mode are “+” in the whole area, “+” for the second mode in the south, and “-” in the north. The “strong in the south (north) and weak in the north (south)” distribution features of extreme summer precipitation are the most obvious in the year, with the maximum (minimum) time coefficient in the second mode. In the typical strong (weak) extreme summer precipitation year, there are (not) cold and warm air convergence in Longdong Region. The ascending (descending) motion in the study area was enhanced, and the outgoing longwave radiation (OLR) anomaly is negative (positive), indicating the convective activity is strong (weak), corresponding to more (less) precipitation. Meanwhile, the convergence (divergence) of water vapor flux is favorable (unfavorable) to the generation of extreme summer precipitation. In conclusion, the atmospheric circulation, dynamic conditions, and water vapor conditions all affect the anomalous changes of extreme summer precipitation in the study area. This paper’s results contribute to a deeper understanding of the characteristics and influencing factors of extreme summer precipitation in the Longdong Region, which provides meaningful references for regional disaster prevention and mitigation.