The influence of El Niño on summer persistent precipitation structure in the middle and lower reaches of the Yangtze River and its possible mechanism

The impacts of El Niño on summer persistent precipitation structure in the middle and lower reaches of the Yangtze River (MLRYZR) are analysised based on daily gauge precipitation data collected at more than 2400 stations from 1961 to 2016. Precipitation events are found to mainly persist for 1 to 5 days with intensity ranging from 4 to 24 mm/d, while the precipitation events persisting beyond 5 days are relatively less with intensity ranging from 12 to 24 mm/d. The frequency and intensity of long persistent events (LPE:> 5 days) are larger to the south of the Yangtze River than to the north. Furthermore, the structure of persistent precipitation is found to change under the impact of El Niño. To the south of the MLRYZR, precipitation events have changed from short (SPE:2 to 5 days) and non-persistent events (NPE:1 day) to LPE, and the intensity of LPE enhences. To the north of the MLRYZR, precipitation events have changed from NPE to SPE, especially in Hubei province, and the intensity of SPE slightly increases. Hence, El Niño can enhence the persistence and intensity of precipitation events. Further analysis shows that El Niño can promote the westward extension of the western Pacific subtropical high, resulting in abundant water vapor transport from the northwest of the subtropical high to MLRYZR. Meanwhile, the block high remains stable in the middle and high latitudes. These mechanisms finally lead to enhancements in persistence and intensity of precipitation events, bringing serious influences on agriculture and economy in MLRYZR.