India just had one of the warmest winters, with temperature breaking century-old records. While this has already set the alarms bell ringing for policy-makers preparing for an early summer of deadly heatwaves, it is also the unusual change in rain pattern that has left the scientists worried.
The weather during winter is mostly influenced by rainy systems called Western Disturbances (WDs). These are extra-tropical storms, which originate over the Mediterranean region, move eastwards towards Iran-Afghanistan, Pakistan and India, where the Himalayas obstruct them and cause rain and snowfall over the region.
But the rising global temperatures have begun to impact these systems, not only making them more dynamic, but altering their frequency as well as intensity. Such has been the impact that winter rains have now been largely evading the Northwest and Central India, leading to rise in maximum temperatures.
Where is the Winter Rain?
On an average, five to six WDs hit the Himalayas every month from December to February (peak season), usually moving across the Jammu and Kashmir region. Out of these, at least two reach the plains and bring winter rains. However, this time, the intensity of these rainy systems was exceptionally low.
December saw as many as seven WDs, but only one was intense enough to bring some rainfall over North India — and it ended as the hottest December in almost 122 years. January, too, recorded seven WDs, out of which, only four impacted the North India and brought rain, snowfall and hailstorm. February saw five successive WDs, which moved across north India. But, most of the systems were feeble, and only caused light to moderate rains.
Overall, out of the 19 such systems, only 5-6 could impact the north-western plains, and bring rains. As former IMD chief KJ Ramesh says, “WDs are forming, but they aren’t impacting the north-western plains as much as they used to. Now, most of the activity is limited to the upper mountainous regions of J&K and Himachal Pradesh.”
While there was significant snowfall in the upper reaches, the amount of rain over the north-western plains remained far below normal. There was a staggering rainfall deficit of -83 per cent in December, which improved to +23 per cent in January, and again plummeted to -76 per cent in February for North-west India.
Impact of Climate Change
This is disconcerting because WDs are not only crucial for India’s short, but significant spell of winters, and agricultural production. The amount and intensity of winter rains impact the Rabi crops like wheat grown during November-February. Winters are indeed becoming warmer all over the globe. But in case of India, the impacts are likely to be much more intense due to the high vulnerability of its burgeoning population.
Scientists investigating these distinct structural changes in the WDs are certain that it is happening due to climate change. With global warming, WDs are getting lighter due to more convection and heat coming in. “Of late, it is seen that all WDs do not precipitate. This means there are days when there is no precipitation happening during their passage and contradictorily there are non-WD days when good amounts of precipitation is seen over North India,” says Dr AP Dimri, director, Indian Institute of Geomagnetism.
The United Nations-led IPCC has already warned of higher temperatures over Indian sub-continent and increased tendency of heatwaves. Projections show that India will experience heat stress conditions in the future, and it is virtually certain that cold days and nights will become fewer.
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