Counter-clockwise epochal shift of the Indian Monsoon Sparse Zone

Abstract

The Indian southwest monsoon season is considered the lifeline of the region's socioeconomic wellbeing. It is recognized that even small variations often lead to notable impacts on the regional economy and agricultural productivity. As a precursor to droughts, this study identifies from century-long data, Monsoon Sparse Zone (MSZ) as a locale with less seasonal rainfall compared to the long-term average climatology. Identifying the MSZ is crucial to understand the spread and propagation of drought-prone areas. The present study investigates the nature of the major MSZ shift in India during the past 116 years (1901–2016) and probable meteorological factors responsible for that transitions. For this purpose, the high-resolution daily rainfall analysis from India Meteorological Department (IMD) and other surface and upper air meteorological parameters from, the NOAA, CRU, and NCEP-NCAR are used. Two drought indices are used to study the MSZ and its epochal shifts during the past century over India. The MSZ locales follow the counter-clockwise shift from west to north-central India through the peninsular region from one to another epoch (each of 29 years) that is statistically significant. The MSZ shifting is insensitive to epochal duration selection. Large-scale and regional processes that may impact the shift of MSZ are analyzed. The El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) have strong influences on the MSZ shift. Additional synergistic effect of large-scale – factors such as westward shifting of subsidence branch of the Walker circulation, the orientation of IOD and local-scale phenomena like the increased surface temperature, moisture flux inflow from the Bay of Bengal, also have shifts aligning to cause this detectable and significant change in the MSZ locales. The presence of MSZ conforms to the drought-prone area over India and has a direct influence on water resources, agriculture, and allied sectors.