Present and future of the South Asian summer monsoon’s rainy season over Northeast India

Abstract An iconic feature of the Indian Summer Monsoon Rainfall (ISMR), a longer than June–September rainy season over Northeast India (NEI), while a much shorter one over northwest India is expected to be altered by climate change but an objective definition of the length of the monsoon rainy season (LRS) over the NEI is lacking. Here, defining the LRS objectively over NEI, we show that the El Niño and Southern Oscillation (ENSO) is a primary driver of LRS, while rainfall during LRS is poorly correlated with the ENSO. In contrast to a significant decreasing trend of LRS and LRS-rainfall during the historical period, the projected LRS under the SSP5–8.5 scenario continues to decrease while the LRS-rainfall acquires a significant increasing trend over NEI. A significant increase in the impact of hydrological disasters is expected over NEI in the future due to the increasing intensity and frequency of extreme rain events within a shorter rainy season.