EXPLAINED: Why Uttarakhand, Himachal, J&K, And UP Are Witnessing Relentless Heavy Rains?

Know the science behind the relentless heavy rains in Uttarakhand, Himachal, J&K, and UP. Read how the monsoon trough and western disturbance are causing floods and landslides.

Commuters wade through heavy rainfall on a road. (Photo: IANS)

Uttarakhand, Himachal Pradesh, Jammu & Kashmir, and sections of Uttar Pradesh are witnessing an intense phase of heavy rain, a process caused by a highly complex combination of atmospheric forces associated with the prevailing monsoon system. Meteorologists link this increased downpour mainly to the current location of the Monsoon Trough and its interaction with a Western Disturbance (WD).

The Monsoon Trough is a long, low-pressure belt that generally runs parallel to the Himalayan foothills. When this trough is over or close to an area, it considerably enhances the chances of developing dense clouds and heavy precipitation. The reason is that the trough functions like a magnet and attracts moisture-laden winds both from the Arabian Sea and the Bay of Bengal, which causes an increased upward air movement (Air Lifting).

Adding to this effect, the present scenario witnesses an upper-level trough, referred to as a Western Disturbance, further strengthening this upward movement of air in these northern states as well as the foothills of the Himalayas. Western Disturbances are meteorological systems originating in the Mediterranean and moving eastward into North India, carrying moisture and cooler air.

The Role Of Atmospheric Divergence

The upper-level Western Disturbance enhances the lift of the air upward by increasing upper-atmospheric divergence, especially to the right of the trough axis. Upper-atmospheric divergence indicates that air is diverging outward at elevated levels, thus resulting in a vacuum effect below that makes lower-level air rise more strongly. Upon its ascent, it cools and becomes cloudy, and since it is moving upward rapidly, it condenses and forms dense clouds and heavy precipitation.

This synergistic effect of the low-level Monsoon Trough pulling moisture and the upper-level Western Disturbance increasing divergence produces conditions for strong convection and heavy, persistent rainfall. It is the very reason for the persistent and heavy rain seen in Uttarakhand, Himachal Pradesh, Jammu & Kashmir, and surrounding regions of Uttar Pradesh. This process not only augments the amount of rain but also increases the danger of hazards such as flash flooding and landslides.

Monsoon Trough And Western Disturbance: A Deadly Pair

Experts describe that this combined impact of the Monsoon Trough and Western Disturbance greatly complicates the weather picture. The Monsoon Trough accumulates moisture at lower levels, but the Western Disturbance almost doubles the strength of rain by enhancing divergence at higher levels. That is why the rainfall is far heavier and longer-lasting than usual monsoon showers.

As per the Meteorological Department, caution and alertness are important in the hit zones in these situations. Himalayan zones are naturally vulnerable, and heavy rainfalls in these zones considerably increase the occurrences of flash floods and landslides. The Monsoon Trough's present closeness to the Himalayan foothills continues to extract moisture from the Bay of Bengal and the Arabian Sea, while the Western Disturbance maintains the convergence and divergence in the upper layer, the intensity of precipitation and convection remaining steady.

Alert Issued For Residents

Given these situations, meteorologists have urged local authorities and citizens of the affected states to stay vigilant. Extra caution is needed in the hilly and riverside regions of Uttarakhand, Himachal Pradesh, Jammu & Kashmir, and Uttar Pradesh, where the danger of sudden increases in water levels and landslides exists.

This is likely to last over the next couple of days, until the Monsoon Trough moves south and the impact of the Western Disturbance weakens. In the meanwhile, constant vigil and active measures of disaster management will be the order of the day in these areas.