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The devastating storms in Uttar Pradesh on May 13 and May 14 that have killed more than 117 people were caused by the interaction of multiple weather systems with wind speeds similar to very severe cyclones in some of the affected areas.
Such powerful winds on land are a symptom of warming and consequent climate change which have led to the slowing down or stilling of planetary scale winds while localised winds in convective storm systems and cyclones have become stronger.
Around 26 districts in both eastern and western Uttar Pradesh have been affected by the thunderstorms that carried fierce winds along with dust and hail. Six places in eastern Uttar Pradesh and seven places in western Uttar Pradesh recorded peak wind speeds in excess of 50 km/hr.
Eight places in total also recorded wind speeds in excess of cyclonic wind speeds of 65 km/hr. One place in eastern Uttar Pradesh and another in western Uttar Pradesh recorded wind speeds of 130 Km/hr which are more the very severe cyclone wind speed threshold of 119 km/hr.
On May 13, the India Meteorological Department (IMD) was tracking a western disturbance over north Pakistan and the neighbouring Jammu region. Western disturbances are extra tropical storms that travel to northwest India from the Mediterranean and the surrounding regions carrying rainfall mainly during winter and spring months. Their activity has lately increased during summer and monsoon months as well while decreasing during the winter period.
There was an upper air cyclonic circulation over northwest Uttar Pradesh and adjoining Uttarakhand and another over south Haryana and its neighbourhood. There was also an upper air cyclonic circulation over southwest Madhya Pradesh and a long low-pressure trough from this circulation to Manipur which could have also influenced the weather over Uttar Pradesh.
The cyclonic circulation over southwest Madhya Pradesh continued its influence on May 14. There were two cyclonic circulations over Uttar Pradesh, one over its east and another over the west. An east west low-pressure trough from southeast Madhya Pradesh to sub–Himalayan West Bengal was also active on this day.
All these weather systems created the conditions for convection and thunderstorms to occur. But the extra energy required for the record breaking very severe cyclone wind speeds could have been provided by the background warming and excess moisture in the atmosphere.
“Warmer atmosphere holds more moisture which becomes like a cycle which we now find ourselves in. This has increased the global average temperature by around 1.2 C in the last 180 years or so,” UC Mohanty, emeritus professor at the School of Earth, Ocean and Climate Sciences, Indian Institute of Technology, Bhubaneswar, told Down To Earth in 2024.
“Winds flow because of the force generated by the pressure differences. If the pressure gradient is higher then the winds will be stronger and vice versa. What we see with the excess warming is that the larger pressure gradient between the equator and polar regions has decreased which slows down planetary winds but locally winds can become stronger,” he added. This additional localised strengthening of wind systems can be observed in various extreme weather events such as tornadoes, cyclones and thunderstorms.