Weakening of Triennial Oscillation of the Indian Summer Monsoon Rainfall (at 1° × 1° Gridded Scale) Under Future Global Warming. Issue 7 (25th July 2019)

• Record Type: Journal Article
• Authors: Jena, Pravat; Azad, Sarita
• Is Part Of: Earth and space science. Volume 6:Issue 7(2019)
• Page Start: 1262
• Page End: 1272
• Publication Date: 2019-07-25
• Subjects: triennial oscillation -- power spectral density -- statistical significant -- confidence level; Space sciences -- Periodicals; Geophysics -- Periodicals; 500.5
• DOI: 10.1029/2019EA000584
• Languages: English
• ISSNs: 2333-5084

Abstract

Abstract: India's agriculture is a significant component of the Gross National Product (GNP) and is largely dependent on the Indian summer monsoon. This makes an accurate prediction of rainfall a key factor in improving agricultural production. A statistical cycle, widely known to have a strong 2.85‐year period and will therefore be called a triennial oscillation here, plays a vital role in such predictions. In the present work, we examine the spatial distribution of this short‐period oscillation at 1° × 1° (lat./long.) resolution using 1, 260‐month data (1901–2005). A power spectral analysis of the observed data set shows that the statistically significant triennial oscillation (at 95% confidence level) is present over 54% of the total number of 354 grids across India, which covers 69.03% area. Projections of selected data from models used in Coupled‐Model Inter‐comparison Project Phase 5 predict weakening of this oscillation (in amplitude) by 2100. The projections indicate reduced confidence levels of this oscillation at 80%, 85%, and 90%, respectively, in 3%, 20%, and 62% of the selected 54% grids, which covers 41.3% area. A weakened triennial monsoon cycle will have a severe impact on agriculture and water resource management, particularly over the southwest‐coastal, northern, and northeast‐central parts of India. Plain Language Summary: An accurate prediction of Indian monsoon rainfall is of utmost importance for many applications like agriculture, water resource management, and extreme events. One of the ways to assess the degree of predictability in the monsoons is by extracting the significant oscillations present in the given data. This work evaluates the presence of triennial oscillation for this purpose and assesses the changes in its magnitude in future projections. The results reveal that the significance levels of this oscillation are decreasing over a large part of the country. Key Points: This study analyzes the spatial distribution of triennial oscillation of Indian summer monsoon rainfall The amplitude of the triennial oscillation is projected to be weakening in future under the RCP 8.5 scenario One‐to‐one correspondence between time and frequency domain is established