How climate change is changing the Indian monsoon
https://lifestyle.livemint.com/amp/news/big-story/dark-clouds-ahead-how-climate-change-is-changing-the-indian-monsoon-111627637725104.htmlClimate change is altering the nature of the Indian monsoon, turning it into an erratic and destructive force. According to climate projections, it promises to get even more unpredictable through the rest of the century. India is one of the most vulnerable nations to the ravages of climate change, and what makes our experience unique in many ways is that the country faces severe challenges on nearly every climate metric: be it sea level rise, the melting of Himalayan glaciers, an increase in the number of destructive cyclones or extreme heatwaves. In many ways, these separate impacts have come together to shape the destiny of one of the most awe-inspiring weather phenomena on the planet, the Indian monsoon.
...
while the monsoon is a robust system and continues to remain so, climate change has added a further layer of variability to a weather system that anyway registers a degree of natural and regional variability. “Now the number of rainy days (in a season) is decreasing. And the length of the dry spells is increasing. There’s not much change in the total amount of rain. The number of rainy days may be small, but when it rains, it will rain very heavily, so that the seasonal total will be same. So there are changes in the daily rainfall activity, that is very obvious,” he says.
...
For every 1 degree Celsius rise in heat, the atmosphere can hold 7% more moisture. This is also due to the rapid heating of the global ocean, which has absorbed 90% of the excess heat generated by man-made climate change in the past 50 years. As a result, extreme rainfall events of the sort seen in Maharashtra would become very common. “We have found that there is a strong relationship of the monsoon with sea surface temperature (SST). One is the way in which it affects the monsoon circulation itself. There appears to be a competition between the changes in ocean temperatures and the land temperatures. Overall the warming (over land) in India in the last century is much less compared to other regions. At the same time, the Indian Ocean temperatures are high and goes up to 1.2 degrees Celsius above normal in some regions,” says Koll.
this is leading to a weakening of the land-sea temperature gradient—the thermal contrast—thus drying the monsoon circulation. At the same time, there is a lot of moisture in the air because of an increase in SST. So even if the monsoon circulation is weak, in certain episodes, like in Maharashtra, strong winds can bring in plenty of moisture from the Arabian Sea region which then falls over land in the form of extreme rainfall
...
over some 900,000 years, monsoon rainfall over India varied according to the amount of CO2 in the atmosphere. “We show that over the last 900,000 years, higher CO2 levels along with associated changes in ice volume and moisture import from the southern hemisphere were associated with more intense monsoon rainfall. That tells us that CO2 levels and associated warming were major players in monsoon intensity in the past, supporting what the models predict about future monsoons — that rainfall will intensify with rising CO2 and warming global temperatures,”
...
“The monsoon is obviously becoming more erratic, and intensifying and you have extreme flood events. But at the same time associated flood events are also increasing. These include landslides, hailstorms, thunderstorms, cloudbursts. Now floods are occurring also in the onset phase as well as the receding phase of the monsoon. And you’re seeing more instances of urban flooding and flash floods” says Mohanty. He points out that microclimates across India are changing. “Forty per cent of India’s districts are showing a swapping trend. Where flood prone areas are becoming drought prone and drought prone areas are becoming flood prone. And the majority of the swapping trends are being witnessed during the monsoon