Contrasting monthly trends of Indian summer monsoon rainfall and related parameters
Recent studies have reported contrasting inferences in the variability and trends of Indian summer monsoon rainfall (ISMR). These studies have analysed the ISMR variability from a seasonal perspective. The present study observed the monthly ISMR trends from June to September for the period 1980–2015.The results show a significant contrasting trend of rainfall over India (in the heavy, moderate as well as low rainfall regions) in each month of the summer season. A significant decline of rainfall is occurring in June over the monsoon onset regions of the southwest coast of India. The rainfall trend over India exhibits a pattern similar to active type (above normal rainfall over central India and below normal in the foothills of Himalayas and southeast India) in July and September, conversely, a pattern similar to break type occurs in August. The monthly variability of summer rainfall is due to the changing pattern of low pressure over the Indian landmass and the associated modulation of zonal and meridional moisture flow as well as low-level vertical motion. The study also observes widespread spatial variability in the monthly trends of ISMR and concludes that the seasonal trend analysis does not reveal the actual pattern in the monthly trends of ISMR.
The author expresses his sincere thanks to IMD, CWC, Dibrugarh (India), Susana Barbosa, Vikraam, Suresh and anonymous reviewers. Sincere thanks to Amrutha Dilip, for the systematic editing of the manuscript.
Compliance with ethical standards
The author declares that there are no competing interests.
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