#Ajayan
Kochi | The tragic demise of two individuals in Kollam on Tuesday, felled by a lightning strike, brings to light the perplexing phenomenon of thunder and lightning during the monsoon season. Traditionally, thunder and lightning were the harbingers of pre-monsoon summer showers or the occasional post-monsoon rains of October and November, called Thulavarsham in Malayalam. However, these fatal displays of nature have now become a frequent occurrence even amid the height of the Southwest monsoon.
Scientists attribute this anomaly to a fundamental shift in weather patterns, a consequence of global warming that has altered the very nature of rainfall. Dr. Chakrapani, a former scientist from CUSAT's atmospheric science department, elucidates that this explains the erratic timing of rainfall and the dramatic fluctuations in the volume of downpours.
While temperature levels have steadily risen, long-term data reveals no definitive increase or decrease in overall rainfall. However, the nature of the downpour has transformed dramatically, with rain that once spanned an entire day now cascading in a mere hour, or a season’s worth of rain deluging within a few days.
The character of rain during pre-monsoon summer showers and post-monsoon Thulavarsham has remained largely unchanged. However, it is during the monsoon period that a significant and noticeable transformation has occurred.
During the monsoon, the skies typically have shallow Cumulus clouds, the fluffy, cotton-like formations that stretch a few kilometers high. However, with rising temperatures, these clouds now expand and ascend to greater heights with increased speed, transforming the monsoon landscape.
It is estimated that a mere one-degree rise in temperature can result in a 7 per cent increase in the water vapour the atmosphere can hold. Naturally, this elevated moisture must descend eventually, explaining the increasingly frequent occurrences of heavy or extreme downpours.
Moreover, higher temperatures induce convection and the upward movement of clouds, leading to their increased vertical extent. This phenomenon, typically observed during summer or in October-November, often results in the discharge of charged particles, manifesting as thunder and lightning. Lightning, an electric discharge, arises from imbalances between storm clouds and the ground, but it can also occur within clouds or between clouds and the surrounding air.
In earlier times, monsoon showers were accompanied by shallow clouds, lacking the sufficient height necessary for electric discharge, thus sparing the season from thunder and lightning. However, in the current climate, marked by high temperatures interspersed with long intervals of rain, we now witness the rise of towering clouds due to their vertical ascent even during the monsoon. The presence of thunder and lightning, even during the night and early morning, signals elevated temperatures that foster the formation of these imposing cloud structures.
A study titled "Variability in Lightning Hazard over Indian Region with Respect to El Niño–Southern Oscillation (ENSO) Phases" by AV Sreenath, S Abhilash, and P Vijaykumar of the Atmospheric Sciences Department at Cochin University of Science and Technology highlights this trend spanning nearly two decades. The research reveals that, regardless of ENSO phases, each year has exhibited above-average lightning flash density (LFD) over Northeast India and the Southern Peninsular regions.
