Mandi: Researchers from the Indian Institute of Technology-Mandi (IIT-Mandi) have developed an algorithm to process 100 years of data of the Indian monsoon rainfall and have predicted a weakening strength of the phenomenon by 2100.
The algorithm will also factor in information about global climate phenomena such as the El Nino Southern Oscillation, and can access periodicity of switching between strong and weak monsoon years.
The research was undertaken by Sarita Azad, Assistant Professor, School of Basic Sciences, along with her research scholars Pravat Jena, Sourabh Garg and Nikhil Ragha.
They studied the changes in the periodicity of monsoon rainfall and used the data to predict periodicity in future.
Their work has recently been published in the reputed American Geophysical Union peer-review international journal Earth and Space Science.
The Indian summer monsoon, the annual cycle of winds coupled with a strong cycle of rains, is undoubtedly India's lifeline.
While the monsoon itself is a stable phenomenon, arriving almost like clockwork every year, the short-term fluctuations in annual rainfall are unpredictable and pose a great challenge.
Azad and her team developed algorithms that can accurately detect intense rainfall events, taking into consideration the triennial oscillation period and other factors such as the El Nino Southern Oscillation.
For this purpose, Jena has developed an algorithm to analyse the changes in periodicity of the monsoon. It predicts a decreasing intensity of rainfall in most parts of the country.
The team examined the spatial distribution of the triennial oscillations using rainfall data of 1,260 months between 1901 and 2005.
They analysed the power spectrum of the observed data and showed that the 2.85-year periodicity was present at 95 per cent confidence level over more than half of the 354 grids across India.
"We found that Indian summer monsoon rainfall has a periodicity of 2.85 years during which the monsoon tends to switch between strong and weak years. This 2.85 year period is called triennial oscillation," Azad said.
In addition to the triennial oscillation, the quantum of rains that occurs during the monsoon is also connected to global climate phenomena such as the El Nino Southern Oscillation that recurs in a three to five-year period.
Understanding the relationship between triennial oscillation, its spatial distribution, and how it is likely to change in future is important for reliable monsoon prediction.
Explaining the phenomenon, Jena said: "The monsoon involves complex interactions both in temporal and spatial scales. Despite complexity, the monsoon rainfall seems to show a well-defined pattern."
The research team has projected the data into a collaborative framework-based simulation called the Coupled Model Inter Comparison Project to ascertain the future pattern of the 2.85-year period oscillation.
The projections showed a weakening of this oscillation by the year 2100.
Azad added: "The triennial oscillation of the monsoon depends on global phenomena such as El Nino Southern Oscillation and the current triennial periodicity of 2.85 years may not hold good in future years, depending on the occurrence and periodicity of El Nino."
Studies have shown that the periodicity of the El Nino Southern Oscillation itself is reducing, most likely linked to global warming, and this would have a direct impact on the strong-weak periodicity of the monsoon.
"A weakened triennial monsoon cycle will have a severe impact on agriculture and water resource management, particularly over the southwest coastal, northern, northeast, and central parts of India," said Jena on the significance of their findings.