Rainfall in Bihar has been less than normal for 18 out of 26 years, indicating a rapid change in the state's rainfall trends over the past 2.5 decades.

The weather pattern in Bihar is no longer as it used to be. The trend of monsoon rainfall in the state has changed rapidly over the past two and a half decades. According to the Indian Meteorological Department, there has been less rainfall than normal in 18 out of the last 26 years. This is due to the shifting of the monsoon trough line. When this trough line is active over Bihar or at the foot of the Himalayas, the state receives good rainfall. In recent years, this trough line has shifted towards central India for an extended period.