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How climate change is altering Indian monsoon – The Hindu

Monsoon in India has undergone several changes over the years, especially on account of climate change. A shift in the track of monsoon systems, like low pressure and depression travelling south of their position and flash floods are a result of this change. And these changes spell intense and frequent extreme unprecedented weather events over the places which once struggled to record even normal monsoon rains. With this looming threat having a bearing on food security, it is only a matter of time before it has socio-economic impact.

“It has been very complex to understand the rainfall variability and how monsoon patterns have been behaving of late, especially this year. The problem is that it is very challenging for us to understand the situation, which calls for a lot more research. Persistence of intense La Nina conditions, the abnormal warming of East Indian Ocean, negative Indian Ocean Dipole (IOD), southward movement of most of the monsoon depressions and lows and pre-monsoon heating over the Himalayan region are melting glaciers. This is a very complex mix,” said Dr. R. Krishnan, Executive Director, Centre for Climate Change Research, Indian Institute of Tropical Meteorology (IITM).

The Indian Meteorological Department (IMD) has clearly sighted that 2022 has seen the second highest extreme events since 1902. An alarming case as incidents of floods and droughts have increased, there is more evidence coming our way on how global warming has been impacting the Indian monsoon.

“There is no doubt about the fact that most of the monsoon weather systems have been travelling across central parts of the country, changing the area of rainfall. Climate change is definitely behind these changes and thus, it calls for more research on the changes in the behavioural pattern of these systems,” said G.P. Sharma, President, Meteorology and Climate Change, Skymet Weather.

How climate change impacts summer monsoon rainfall
Places that once recorded excess rainfall are today rainfall deficit
1. It is complex to understand the rainfall variability and how monsoon patterns have been behaving of late, particularly this year
2. Alarming increase in floods and droughts provides direct evidence of how global warming has been impacting the Indian monsoon
3. Madhya Pradesh, Gujarat, Rajasthan and parts of Maharashtra have recorded excess rainfall this year
4. In contrast, West Bengal, Jharkhand and Bihar did not receive normal rains
5. Back-to-back active monsoon systems in the Bay of Bengal in July led to excess rainfall to the tune of 8% — actual rainfall recorded was 472.8 mm as against the normal of 437.2 mm
6. August too saw two back-to-back depressions forming in the Bay of Bengal and travelling across Central India
7. While summer monsoon rainfall each year is unique, there has been a large regional and temporal variability in rainfall this year
8. There is evidence that global warming increases the fluctuations in the monsoon, resulting in both long dry periods and short spells of heavy rains

Excess and deficit

As a result, States such as Madhya Pradesh, Gujarat, Rajasthan and parts of Maharashtra have been recording excess rainfall this season. Usually, monsoon systems move across Northwest India giving rains over the region there. Experts believe that these changes are here to stay, which would continue to propel extreme weather events over the entire South Asian region.

During the last six months, entire South Asia has been reporting a series of extreme weather events. While Bangladesh, Pakistan and India have battled severe floods, China is reeling under massive drought conditions.

“Slow onsets can still be taken care of through adaptation and resilience ideas but these kinds of big events are very difficult to cope with. That is where the main issue lies as the country would then have to divert development money to climate finance to combat climate change.” said Dr. Anjal Prakash, Research Director, Bharti Institute of Public Policy, Indian School of Business and IPCC lead author.

After a weak onset, monsoon went into a lull and so no thumping activity was seen in Kerala and adjoining parts of Karnataka. By June, monsoon had reached the plains but the onset was not a strong one. This resulted in West Bengal, Jharkhand and Bihar not receiving normal rains. Back-to-back active monsoon systems in the Bay of Bengal in July led to excess rainfall to the tune of 8% — actual rainfall recorded was 472.8 mm as against the normal of 437.2 mm.

“August too saw two back-to-back depressions forming in the Bay of Bengal and travelling across Central India. These intense systems in quick succession kept the monsoon trough well south of its normal position for most of August,” explains Mahesh Palawat, Vice President, Meteorology and Climate Change, Skymet Weather.

Rice production

“Monsoon each year is unique, but we did see a large regional and temporal variability in rainfall this year. Our research shows that global warming increases the fluctuations in the monsoon, resulting in both long dry periods and short spells of heavy rains. This year, the monsoon was potentially influenced by La Nina also — the cooler than usual Pacific conditions,” said Dr. Roxy Mathew Koll, Climate Scientist, Indian Institute of Tropical Meteorology.

One of the major impacts of changes in track of monsoon systems can be seen on kharif crops, particularly rice production. They form a significant share of more than 50% of total food grain production during this period.

“Arrival of monsoon and whether onset would be strong or weak will always continue to dodge us. Due to southward movement of majors, all main monsoon low pressure areas and depressions, rice producing States such as West Bengal, Bihar, Jharkhand and east Uttar Pradesh have been deficit by large margins. This would straight away have an impact on the quantity as well as the quality of the crop,” said Mr. Palawat.

Bihar, West Bengal and Uttar Pradesh, which account for a third of the country’s total rice production, have been highly deficit despite an active monsoon current in July and August.

These uneven distribution rains along with increasing temperatures and humidity give rise to pest attacks and diseases. This will, in turn, impact the quality of the grain as well as the nutrition value may vary. According to a study, ‘Climate change, the monsoon, and rice yield in India’, very high temperatures (> 35°C) induce heat stress and affect plant physiological processes, leading to spikelet sterility, non-viable pollen and reduced grain quality. Drought, on the other hand, reduces plant transpiration rates and may result in leaf rolling and drying, reduction in leaf expansion rates and plant biomass, immobilisation of solutes and increased heat stress of leaves.

Recent research indicates that monsoon rainfall became less frequent but more intense in India during the latter half of the 20th century. Scientists and food experts believe that a better rainfall scenario could have helped increase the harvest. However, India’s hundreds of millions of rice producers and consumers are being affected negatively with these unprecedented changes which are also raising concerns over food security.

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