Extending seasonal predictability of Yangtze River summer floods

Abstract. Extreme pluvial floods across China's Yangtze River basin in the summer of 2016 were strongly connected with intense atmospheric moisture transport, and resulted in vast loss of properties after a strong El Niño winter. Predicting such extreme floods in advance is essential for hazard mitigation, but the flood forecast skill is relatively low due to the limited predictability of summer precipitation. By using a “perfect model” assumption, here we show that atmospheric moisture flux has a higher potential predictability than precipitation over the Yangtze River at seasonal timescales. The predictability of precipitation and moisture flux is higher in post-El Niño summers than in post-La Niñas, especially for flooding events. As compared with extreme precipitation, the potential detectability of extreme moisture flux increases by 20 % in post-El Niño summers, which suggests that atmospheric moisture flux could be crucial for early warning of Yangtze River summer floods.