Technical noteEl Niño Southern Oscillation cycle indicator for modeling extreme rainfall intensity over India

- Change in ENSO-Extreme rainfall relationship due to ENSO index choice is examined.
- SOI is the best ENSO index for modeling extreme rainfall over India.
- ENSO-Extreme rainfall relationship is changing significantly due to ENSO index choice.

Since the global climate change altering the characteristics of extreme rainfall events, modeling the behavior of extreme rainfall is becoming indispensable. Among various physical processes, the El Niño Southern Oscillation (ENSO) cycle is a significant process that can trigger occurrences of extreme hydro-climatological events, such as floods, droughts and cyclones. Consequently, modeling the relationship between ENSO cycle and regional climate anomaly is gaining more attention in recent years. Studies in literature used various ENSO indices to quantify ENSO cycle in the statistical models which aim to model/forecast extreme rainfall and fail to report the best ENSO index for modeling extreme rainfall over India. Hence, this study is carried out to answer two research questions: (1) What is the best ENSO index for modeling extreme rainfall intensity over India? (2) What is the significance of identifying the best ENSO indicator for modeling extreme rainfall intensity over India? Towards answering these questions, the change in the linear relationship between ENSO cycle and extreme rainfall over India due to the choice of ENSO cycle indicator is examined. Results of this study indicate that the ENSO index Southern Oscillation Index (SOI) is the best ENSO index for modeling extreme rainfall over India. The results also show a significant change in ENSO-Extreme rainfall relationship due to the choice of ENSO index. In particular, 42% is the average increase in correlation coefficient between monsoon season extreme rainfall and ENSO cycle when the best ENSO index is chosen instead of the second-best ENSO index and it is around 37% for the non-monsoon season.