Monsoon onset likely to be more frequent in May
A study led by P.S. Biju of the India Meteorological Department found that the southwest monsoon onset in Kerala has shifted predominantly to May from June in recent decades, linked to global warming, while overall rainfall declines but extreme downpours increase in central and northern Kerala. The 124-year analysis reveals a 57-time May onset (1901–2025) versus 68 June occurrences, with rising summer rainfall and a 26 cm per decade decline in monsoon rainfall, necessitating climate adaptation strategies for the state.
Researchers from the India Meteorological Department (IMD), led by senior scientist P.S. Biju, analyzed southwest monsoon onset data from 1901 to 2025 and found that the monsoon now frequently begins in May instead of June, a shift attributed to global warming. The study, published in the *Journal of Agrometeorology*, shows the monsoon onset occurred 57 times in May and 68 times in June over the 124-year period, with early onsets rising to 14 instances post-2000. While overall monsoon rainfall in Kerala is declining by 26 cm per decade, extreme downpours have intensified in central and northern Kerala, increasing flood risks near the Western Ghats. The study highlights a paradox: despite fewer total rainfall days, severe weather events are escalating, particularly in northern and central Kerala. Coastal regions, however, show a decrease in extreme rainfall. Average annual rainfall across Kerala remains around 2,920 mm, though spatial variations exist, with northern districts receiving the highest monsoon rainfall (2,300–3,000 mm) and southern regions often recording less than 1,500 mm. Summer rainfall has slightly increased, while the northeast monsoon trend is declining. Biju explained that global warming accelerates the formation of low-pressure systems over land, altering monsoon winds and causing earlier onsets. The IMD data suggests this trend will likely continue, requiring urgent climate adaptation measures. The researchers emphasize the need for district-specific flood management, improved water storage, and climate-resilient agricultural planning to address Kerala’s shifting rainfall patterns. The study underscores the urgency of climate action, as changing monsoon behavior threatens water resources, agriculture, and infrastructure. With extreme weather events becoming more frequent, Kerala’s vulnerability to floods and droughts has heightened, demanding proactive policy responses. The findings align with broader global observations linking climate change to erratic monsoon behavior.
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