School of Geography and Tourism,Shaanxi Normal University
夏季昼晴夜雨，是典型的日尺度复合极端天气事件。明晰夏季昼晴夜雨强度与气候变暖的响应关系，对中国南北过渡带土壤侵蚀防治具有重要的意义。基于逐日降水数据，辅以BG分割法、经验正交函数（EOF）和Lasso回归等方法，论文对1970—2020年秦岭南北夏季昼晴夜雨强度时空变化特征及影响因素进行分析。结果表明：① 1970—2020年，秦岭南北夏季昼晴夜雨强度呈现显著增加趋势。其中，汉江谷地夏季昼晴夜雨强度（0.30 mm/（d·10a））增加更为明显。② 秦岭南北夏季昼晴夜雨强度主导空间模态为：“全区一致、谷地异常程度高于山地”，说明谷地—平原区，为夏季昼晴夜雨强度变化的敏感区。在时间上，2003—2020年，主导空间模态突变增强，夏季昼晴夜雨强度“南高北低”的格局正在改变，关中平原与汉江谷地成为夏季昼晴夜雨强度增加的高值区。③ 在影响因素上，秦岭南坡、汉江谷地夏季昼晴夜雨强度变化与气象因子相关性高于关中平原。其中，秦岭南坡夏季昼晴夜雨强度主导气象因子为日照时数，而汉江谷地夏季昼晴夜雨强度变化受日照时数、平均风速的共同影响。当夏季昼晴夜雨同期日照时数越长时，秦岭南坡夏季昼晴夜雨强度越大；同期平均风速越大，汉江谷地夏季昼晴夜雨强度越大。
Day sunny and night rainfall in summer is a typical kind of compound extreme events at daily scale. The study of response relationship between the intensity of summer day sunny and night rainfall (DSNR) and climate warming, is of great importance for the control of soil erosion in China’s north-south transition zone. Based on daily precipitation data in summer (June to August) of 72 meteorological stations, assisted by B-G segmentation, empirical orthogonal function (EOF) method and Lasso regression model, we analyzed the spatiotemporal variation and influencing factors of the intensity of DSNR at summertime in the north and south of Qinling mountains during the period 1970-2020. The results showed that: (1) From 1970 to 2020, the intensity of DSNR in summer exhibited a significantly increasing trend, which was more obvious in Hanjiang River Valley (0.30 mm/(d·10a)). (2) The leading mode of the intensity of summer DSNR was characterized by “consistence in the whole region, with a higher degree of anomalies in the valleys than in the mountains”. It indicated that valley-plain areas were sensitive to variations in the intensity of DSNR at summertime. Temporally, between 2003 and 2020, the spatial pattern of “lower in the north but higher in the south” in the intensity of summer DSNR is changing, and consequently Guanzhong Plain and Hanjiang River Valley have become high value areas of increasing summer DSNR intensity in the north and south of Qinling mountains. (3) In terms of influencing factors, the correlation between evolution in the intensity of DSNR at summertime and meteorological factors in the Hanjiang River Valley and southern slopes of Qinling Mountains was higher than that in Guanzhong Plain. In addition, cumulative duration of sunshine was the leading climatic factor driving the changes of summer DSNR intensity in the northern slopes of Qinling Mountains, while the variations of summer DSNR intensity in the Hanjiang River Valley was jointly influenced by cumulative duration of sunshine and average wind speed. To be specific, the intensity of DSNR at summertime in the southern slopes of Qinling Mountains and Hanjiang River Valley showed a positive change relationship with cumulative duration of sunshine and average wind speed, respectively.