资源环境科技发展态势分析平台

Skillful prediction of the Indian summer monsoon rainfall (ISMR) has been a bottleneck problem for more than 100 years. The low seasonal predictability is attributed primarily to the chaotic nature of the sub‐seasonal variability. Here we show that these sub‐seasonal variability rather have significant predictable contributions to the seasonal ISMR, varying on the interannual to multi‐decadal time scale. The sub‐seasonal modes being the building blocks of the monsoon, their net linear contribution may approximate to the predictability limit of the ISMR. It is estimated that an average of about 76% (R ∼ 0.87) of the ISMR variance predictable around 1960s is decreased to about 64% (R ∼ 0.79) in the recent past four decades. It is suggested that improvements in the simulation of sub‐seasonal, particularly the synoptic variability will be key to further improve the seasonal ISMR forecast skill.