Wettest Sept in 102 Years: Monsoon magic & mayhem
We welcome rain after the intense heat of June – it quenches our parched ground, fills ponds and lakes and gives a new lease of life to flora and fauna. In the words of great poet Kalidas, meeting of earth and clouds is nothing less than a kind of lovemaking. At the same time, we demonise rain if it stays longer and go beyond mid of September – just like a guest who decides to stays longer! This pattern of rainfall is nothing new, in fact the Indian monsoon system is very old – at least 12 to 15 million years old.
Scientists have confirmed that monsoon first became strong around 10 million years ago. Since then, the amount of rainfall has varied dramatically due to asymmetric heating and cooling of land and sea, largely linked to global climate change – which is happening even before human being appeared on earth. Extreme weather has been the norm for a long time.
This year we had the wettest September breaking the historical record of 102 years. We also had the highest monsoon rainfall in 25 years. During September, India received an average of 259.3 mm of rainfall, which is the highest since 1917 and second highest in recorded history. We define ‘excess’ monsoon year, if JuneSeptember rainfall exceeds 10% or more above the long-period average. It is also to mention that out of past 19 years, 16 years were drought years. A series of lowpressure systems from the Bay of Bengal persisted longer-thanusual together with depression over Gujarat and cyclonic circulations over Punjab and Bihar kept the monsoon active resulting in the wettest September of the century. Most of the rainfall – around 80%, happens in few days out of four months between June and September. Our entire landscape, ecosystem, and livelihoods depend upon this dramatic climatic phenomenon that renews our hope and aspiration. With rain deserts of Rajasthan turn into vivid green grasslands and flow in our Himalayan and plain-fed rivers increases manifolds.
Monsoons can be understood as large-scale sea breezes which occur when land gets significantly warmer or cooler than the temperature of the ocean. These asymmetric temperature differences are due to differential heat absorbing capacity of oceans and land.
In simple words, sunlight heats the surfaces of both land and oceans, but land temperature rises more quickly than water. When land becomes warmer, the air above it expands and a low-pressure zone is developed. In comparision, ocean remains at lower temperature and the air above it creates a high-pressure zone.
This difference in pressure causes sea breezes to blow from the ocean to the land, bringing moisture-laden air in the form of summer monsoon. The moisture-laden winds on reaching the southernmost point of the Indian, gets divided into two parts due to its topography – the Arabian Sea Branch and the Bay of Bengal Branch.
The Arabian Sea Branch of the Southwest monsoon hits the Western Ghats of the coastal state of Kerala around first week of June, moving northwards along the Western Ghats (Konkan and Goa) with heavy rainfall in coastal areas. The eastern areas of the Western Ghats do not receive much rain from this monsoon as the wind does not cross the Western Ghats.
The Bay of Bengal Branch of Southwest monsoon heads towards North-East and West Bengal, picking up more moisture from the Bay of Bengal. The moisture-laden winds turn further west, travelling over the Indo-Gangetic Plain.
With heavy rain, our houses and streets are waterlogged and settlements are flooded despite having drainage systems. This is because we have encroached upon natural drainage; we have constructed our houses on flood pathways by filling wetlands and lakes.
The flooding which used to wither away in two days due to unaltered natural drainage, now takes one week to fifteen days to ease. Given the earth’s unique topography and arrangement of sea and land as well as the flow of heat from equator to pole, such dramatic season has existed in the past and will exist in future too. However, increasing the atmospheric CO2 and other green-house gases will increase the monsoonal precipitation significantly.
The flooding that goes with such rains is expected to become worse and wider-spread with warming of the planet. And, if we don’t respect nature’s way of draining water to river and the sea through natural channels and waterbodies, we are bound to get flooded. It is not a rocket science!