The asymmetric response of Yangtze river basin summer rainfall to El Nino/La Nina

The Yangtze river basin, in South East China, experiences anomalously high precipitation in summers following El Nino. This can lead to extensive flooding and loss of life. However, the response following La Nina has not been well documented. In this study, the response of Yangtze summer rainfall to El Nino/La Nina is found to be asymmetric, with no significant response following La Nina. The nature of this asymmetric response is found to be in good agreement with that simulated by the Met Office seasonal forecast system. Yangtze summer rainfall correlates positively with spring sea surface temperatures in the Indian Ocean and northwest Pacific. Indian Ocean sea surface temperatures are found to respond linearly to El Nino/La Nina, and to have a linear impact on Yangtze summer rainfall. However, northwest Pacific sea surface temperatures respond much more strongly following El Nino and, further, correlate more strongly with positive rainfall years. It is concluded that, whilst delayed Indian Ocean signals may influence summer Yangtze rainfall, it is likely that they do not lead to the asymmetric nature of the rainfall response to El Nino/La Nina.