B'lore scientists discover changing patterns of El Nino influence

In what may improve the accuracy in rain forecasting in future, climate researchers in Bangalore have found that influence of the dreaded El Nino on Indian monsoon has slowly changed over decades.

An unusual warming of the ocean, El Nino is a climate phenomenon that plays havoc with the weather all over the world. For India, it means deficient rainfall, though there are exceptions. It’s reverse, known as La Nina, means more rainfall.

But the trend has changed in the last 150 years. While El Nino-La Nina effects were more certain and direct between 1871 and 1941, Indian Ocean Dipole (IOD) – a regional climatic factor – became more prominent since early 1940s, claimed the researchers.

Now extreme rainfall events are influenced more by IOD – a temperature sea-saw in the Indian Ocean. The change is visible between 1942 and 2011.

“Any further strengthening of the IOD influence due to warming of the atmosphere and oceans could further affect the frequency of extreme rain events in India,” said Jagdish Krishnaswamy from the Ashoka Trust for Research in Ecology and Environment, Bangalore, who is lead author of the study.

Rainfall less than 100 mm per day is still largely impacted by La Nina, associated with copious rainfall. But IOD overtakes extreme rain events where the precipitation is more than 100 mm. Moreover, they found La Nina and positive IOD leading to more rainfall do not occur in the same year.

“The study suggests older generation weather forecast models will not work as the nature of La Nina or IOD influence is changing,” Krishnaswamy told Deccan Herald.

As India has witnessed an increase in heavy rainfall events in the recent decades, better knowledge of the factors can lead to betterment of existing forecast models.

“Improvement in modelling can enhance the forecasting accuracy of monsoon and extreme events,” the team comprising scientists from Bangalore, Puducherry, the UK and US reported in the latest issue of the journal Climate Dynamics.