NEW DELHI: Floods in Pakistan have killed more than 1,000 people after what its climate change minister called a record unbroken cycle of monsoon rains with “eight weeks of uninterrupted torrents”.
AFP explains what the monsoon is, why it is so important and yet so dangerous, and how climate change and other human-made effects can alter the vast, life-giving yet destructive annual weather system.
What is the South Asian Monsoon?
The Southwest or Asian summer monsoon is basically a colossal sea breeze that brings South Asia 70-80% of its annual rainfall between June and September each year.
It occurs when summer heat warms the landmass of the subcontinent, causing air to rise and drawing in cooler winds from the Indian Ocean which then produce huge volumes of rain.
Why is this important?
The monsoon is vital for agriculture and therefore for the livelihoods of millions of farmers and for food security in the impoverished region of around two billion people.
But it brings destruction every year in landslides and floods. Melting glaciers are increasing the volume of water while unregulated construction in flood-prone areas is adding to the damage.
Is it the same every year?
Although widely studied, the monsoon is relatively poorly understood. It is difficult to predict exactly where and when the rain will fall and it varies considerably.
This year, for example, while Pakistan experienced a deluge, eastern and northeastern India reportedly saw the lowest rainfall in July in 122 years.
What explains the variability?
The fluctuations are caused by changes in global atmospheric and ocean conditions, such as the El Nino effect in the Pacific and a phenomenon called the Equatorial Indian Ocean Oscillation (EQUINOO) discovered only in 2002.
Other factors are thought to include local effects such as aerosols, clouds of dust blowing in from the Sahara Desert, air pollution, and even irrigation by farmers.
What about climate change?
India is warming up and recent years have seen more cyclones, but scientists aren’t sure exactly how a warming planet affects the very complex monsoon.
A study last year by the Potsdam Institute for Climate Impact Research (PIK) of monsoon changes from the mid-20th century suggested it was getting stronger and more erratic.
Initially, aerosol pollution reflecting sunlight moderated rainfall, but from the 1980s the warming effects of greenhouse gases began to cause heavier and more volatile rainy seasons, according to the report. ‘study.
Do other studies confirm this?
Basically yes. The Indian government’s first assessment of climate change, published in 2020, indicates that overall monsoon rainfall fell by around 6% between 1951 and 2015.
He said there was an “emerging consensus” that this was due to aerosol pollution significantly offsetting the expected increase in rainfall due to global warming.
With continued warming and lower aerosol emissions, he predicted more rain and greater variability by the end of this century, as well as “substantial increases” in daily extreme rainfall.
What will this mean for people?
The Indian monsoon of 2021 is a good example of this: June rains were above normal, in July they fell, August was almost a drought and in September the rains returned with a vengeance.
Several hundred people died in floods in Maharashtra in July and Gujarat in September. In the same month, a downpour turned the streets of Hyderabad into raging rivers in just two hours.
But in October, farmers in parts of northern and northeastern India were reeling from drought, while elsewhere the monsoon took longer than usual to recede.
“More chaos in Indian monsoon rainfall will make adaptation more difficult,” Anders Levermann of PIK and Columbia University told AFP last year.