Global-scale interdecadal variability a skillful predictor at decadal-to-multidecadal timescales for Sahelian and Indian Monsoon Rainfall

Manish K Joshi,Ashwini Kulkarni,Archana Rai

doi:10.1038/s41612-021-00227-1

Abstract

In the present study, a sea surface temperature-based index named global-scale interdecadal variability (GIV) encompassing the combined variability of Atlantic multidecadal oscillation (AMO) and interdecadal Pacific oscillation (IPO) has been proposed. The warm phase of GIV exhibits a “cold AMO-like” pattern in the Atlantic basin and a “warm IPO-like” pattern in the Pacific basin. About 84% (R ~−0.914) of Sahelian and 42% (R ~−0.647) of Indian rainfall’s temporal variance is attributed to GIV, showing substantial improvement compared to the variance explained by AMO and IPO individually. The physical mechanism for GIV-rainfall teleconnection is related to a modification of the Walker circulation. Although there is a substantial degree of uncertainty in the current generation of state-of-the-art climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), some still replicate the observed GIV’s spatial structure, its teleconnection, and associated physical mechanism. The results presented herein advance our knowledge about rainfall’s interdecadal variability and have imperative ramifications for developing skillful decadal predictions.

Highlights

Besides having variations on intraseasonal-to-interannual timescales, the Indian monsoon1–6 and Sahelian monsoon7–11 exhibit pronounced variability at interdecadal timescales, having alternate epochs of aboveand below-normal rainfall
global-scale interdecadal variability (GIV) epitomizes the combined interplay of Atlantic multidecadal oscillation (AMO) and interdecadal Pacific oscillation (IPO)
Global-scale interdecadal variability Using observational data, the present study suggests that a global sea surface temperature (SST) illustrates a dominant mode of variability at interdecadal, i.e., D2M timescales (hereafter referred to as global-scale interdecadal variability (GIV))

Summary

INTRODUCTION

Besides having variations on intraseasonal-to-interannual timescales, the Indian monsoon and Sahelian monsoon exhibit pronounced variability at interdecadal (i.e., decadal-tomultidecadal; D2M) timescales, having alternate epochs of aboveand below-normal rainfall. Inspired by the previous studies, an index is proposed that encompasses their combined variability and will serve as a skillful predictor compared to AMO and IPO This index will be of great importance and considered a worthwhile pursuit to understand the D2M variability and prediction of rainfall over respective regions. An attempt has been made to offer an SST-based index that contains D2M variability from the global oceanic basins, precisely the Pacific and North Atlantic Oceans It has been explored how this index is associated with the interdecadal variability of rainfall over Sahel and India, and what is the probable candidate mechanism responsible for such teleconnections

RESULTS

DISCUSSION

Methodology

CODE AVAILABILITY