We are currently in a low rainfall epoch and can expect more below-normal monsoons for next few yearsThe monsoon is a very robust system. If you take the last 150 years of observation data, you find that monsoon has not changed much in terms of all-India average rainfall. But there are regional changes. For example, Chhattisgarh and parts of Odisha are getting less rain whereas Maharashtra, parts of Karnataka, Gujarat, J&K and some other places are getting more rainfall.
Monsoon also has a large multi-decadal oscillation that’s well proven. This cycle spans around 60 years encompassing epochs of low and high rainfall. In some decades you will have more droughts. We are currently in a low epoch and can expect more below-normal monsoons for the next few years. Monsoons in the 1990s were good. But 2000 onwards, it again started going down. We have had drought years in 2002, 2004, 2009, 2014 and 2016.
In the coming years, how is global warming expected to impact the monsoon?
The total quantum of rainfall is not expected to change. During the 122 days of the monsoon season, we do not have rain all the time. Monsoon goes through active and break spells.
What we have found is that the length of the dry spells is increasing.
So, instead of eight days of dry weather, we may have ten days in future. And since the total quantum of rainfall is not changing much, this means that when it rains, it rains very heavily. The number of rainy days may reduce.
This finding is very robust and has implications for agriculture. Farmers will have to think of storing water in tanks, ponds, etc during rainy spells and use this water during the dry periods.
IMD’s monsoon forecasts over the past five years have been consistently more optimistic than actual rainfall. Does it have a positive bias?
I’m not sure about the bias. Being a statistical model, there will be a bias. But whether it is positive or negative, I can’t say.
https://timesofindia.indiatimes.com/blo ... few-years/This is what most of the world is predicted to face in ever increasing extremes with increasing GW. Rains, when they fall, will be ever more intense and devastating, bringing ever worse flooding and washing away crops and other flora. Droughts in between these ever-more-intense deluges will be ever longer and deeper, also destroying crops and desiccating, weakening and killing other plants and trees (those that hadn't been washed away in the last deluge). What ever survives will be weaker and less able to withstand the next even more extreme deluge, roots weakened by drought failing to hold plants and trees in place.
This is the basic process (though there are a variety of others) responsible for wiping out so much of terrestrial life during the earlier GW-induced mass extinction events...once the plants go, the animal life that depended on them inevitably go, too. For scholarly articles about this, see the reference section of the very well researched book
Six Degrees, though it is now getting a bit long in the tooth. Maybe it's time for Lynas or someone else to write an update??