Analysis of monsoon data pertaining to the past 45 years by the Indian Institute of Tropical Meteorology has revealed that while rainfall has shown an increasing trend in northwest India, there has been a decline in the Gangetic Plains – considered the food bowl of India. This has serious implications not only for food security, but also impacts irrigation infrastructure and groundwater resources.
“The Gangetic plain drying trend during monsoon season is a severe concern, because the rain during the summer monsoon not only affects the kharif crops sown during the concurrent summer season, but also the rabi crops sown during the succeeding winter season harvests,” the study states.
“The drying trend puts massive pressure on irrigation infrastructure, resulting in a heavy load on the power supply and maintaining the groundwater table. Despite all efforts, it results in low food grain production, which will create serious challenges to India's food security in the coming years,” the study, published by the India Meteorological Department (IMD) this month adds.
The global climate shift observed during the late-seventies along with the global warming of the atmosphere and tropical oceans has altered the regular spatio-temporal distribution of precipitation, the study observes.
The Indian rainfall during different seasons has observed such abrupt, substantial and persistent shifts and changes around the late-seventies. Due to this major shift, the tropical climate system has undergone significant changes on the long-term inter-annual timescale, the study points out.
The researchers observed that the changing increasing-decreasing trend in the monsoon is connected to the warming of the south-central equatorial Indian Ocean. The warming increases convection and the drops in surface pressure trend over the tropical western Indian Ocean and Somalia.
The drop in surface pressure over Somalia has built up a pressure gradient between the south Indian Ocean and Somalia, which amplified the moisture accumulation towards the western Arabian Sea from the south Indian Ocean. This provides sufficient moisture to western India.
In contrast, the rise in surface pressure north of India and the drop in surface pressure over the tropical western Indian Ocean has declined the pressure gradient between the tropical western Indian Ocean and north India, which had turned down the monsoonal flow towards north India, diminishing the moisture supply and resulting in decreasing trend towards the Gangetic Plains.
The study also pointed out that rising surface temperatures over north-eastern Europe as well as the warming of the Arctic, which is almost three times as fast as the global rate due to the unique features in the Arctic climate system, create environmental and meteorological conditions which increase the monsoon trend towards western India.
