The recent torrential monsoon rains in Uttarakhand and the subsequent floods which left thousands dead and caused extensive damage to property and institutions in the region could have been caused, surprisingly, by the paucity of low-pressure systems (convective activity) in the Western Pacific Ocean. So, hypothesises Dr. M.R. Ramesh Kumar.
Dr. Kumar is Chief Scientist, Physical Oceanography Division, National Institute of Oceanography, Goa. Convective activity in Bay of Bengal and Eastern Equatorial Indian Ocean brings rainfall over the subcontinent while convective activity in the Western Pacific Ocean diverts rain-bearing winds away from the subcontinent.
The monsoon advanced and covered the subcontinent a whole month ahead of usual and brought copious rainfall all over, including Uttarakhand.
In the months of March, April and May there were very few convective systems in the Western Pacific Ocean while there was ample convective activity in the Bay of Bengal and Eastern Equatorial Indian Ocean.
Dr. Kumar explained in a telephone communication to this correspondent that convective activity is associated with low pressure systems and these attract moisture-bearing winds.
In the ‘competition’ to attract moisture-bearing winds, Bay of Bengal came first due to high convectional activity followed by Eastern Equatorial Indian Ocean while the Western Pacific lost out due to low convection.
This brought about a rapid advance of the monsoon across the subcontinent by winds originating in the western Indian Ocean (including Arabian Sea).
Another cause for heavy flooding of rivers, explains Dr. Kumar, was that it snowed heavily in the Himalayas in the pre-monsoon season (March, April and May). By June, the snow started melting, thereby increasing the water levels in rivers which originate from the Himalayas or downstream of the Himalayas.
Another contributing factor was the intense rainfall events in the month of June, which actually helped in causing the snow to melt much faster.
Explaining the role of rainfall in snow and ice melting, Dr. Kumar notes in an email to this correspondent: “Water, which has a higher heat capacity than air, helps in melting of snow or ice much faster when they come in contact with it even when both air and water have the same temperature. The molecules in liquid water are more tightly packed than the molecules in air, allowing more contact with the snow or ice and a greater rate of heat transfer. This accelerates the process of snow and ice melting.”