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In what might be another significant impact of climate change on the Indian monsoon, the unexpected increase in rainfall across the western states of Gujarat, Maharashtra and Rajasthan during August and September might be the sign of a directional shift in the trajectory of the monsoon. This is being increasingly seen in the last few years as heavy downpours have been leading to widespread flooding in these states, pointing to a change in the regional rainfall distribution with questions being raised about its long-term implications throughout the country.
The shift
Traditionally, the low pressure systems formed in the Bay of Bengal region used to move northwest leading to good amounts of rainfall in states like Uttar Pradesh, Bihar, Punjab and Haryana. But nowadays, these systems seem to be moving from the east to the west resulting in above-normal rainfall in comparatively drier states like Rajasthan and Gujarat. This in turn is leading to drier northern states.
The recent Gujarat floods that occurred in the second half of August is an example of the shift in pattern. Many regions in the state have recorded an amount of rainfall recently which is rare at this time of the year, according to records.
Studies have also found that monsoon patterns in India are shifting and have been erratic in the last decade or so, mainly driven by climate change. The study noted that there has been a significant increase in the amount of rainfall in traditionally drier states, like Rajasthan, Gujarat.
“This shift is partly attributed to extensive agriculture practices over the northwest region, which alter local atmospheric conditions. Excess irrigation and increased aerosol content above central India are contributing to the decline in Walker circulation. Additionally, higher temperatures are driving a significant influx of moisture from the land over Western India, enhancing cloud formation and condensation in that region before the monsoon systems move northwards,” Dr Kasiapillai S. Kasiviswanathan, Associate Professor, Dept. of Water Resources Development and Management at the Indian Institute of Technology Roorkee, was quoted as saying by India Today.
Asna – A rare August cyclone!
In a rare phenomena, Asna, a rare cyclonic storm formed over the Arabian Sea on August 30, before originating as a ‘low-pressure’ system over the Bay of Bengal on August 16. The weather system criss-crossed the entire landmass of India from east to west during this period eventually forming a deep depression over Saurashtra and Kutch in Gujarat.
According to reports quoting IMD sources, this is only the fourth cyclone to have developed in the Arabian sea in August since 1944. Such cyclones usually form in South Asia during the pre-Monsoon (March-May) or the post-Monsoon (October-December) period, with a total of 28 such systems forming over the Bay of Bengal in the month of August in the last 132 years.
Experts have cited the reason for these unusual occurrences as an unusual monsoon wind system in the current season besides soil moisture.
Raghu Murtugudde, IIT Bombay professor, and emeritus professor, University of Maryland, wrote in The Hindu, “Ocean-born depressions can feed off of prior rainfall (as soil moisture) as they pass over India…The unusual growth of the low-pressure system that brought deluges to western India fed off the soil moisture from excess rainfall since the beginning of the season…Once its transition to the ocean is complete, it can be expected to grow into a regular cyclone, but as a remarkably unusual land-born cyclone. The warming over the Arabian Sea has already been reported to be related to the northward shift of the low-level jet, which itself is driven by rapid warming over West Asia.”
References:
India continues to witness extreme weather, Gujarat floods kill 16
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