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Abu Dhabi, UAEMonday 18 June 2018

How NYUAD research hopes to predict crucial changes to India's monsoons

Rains are essential to agriculture - as is understanding how climate change may alter them

An Indian boy inspects his paddy fields submerged by monsoon rain in Nagaon district of Assam state, India. EPA
An Indian boy inspects his paddy fields submerged by monsoon rain in Nagaon district of Assam state, India. EPA

Over the centuries, life in Arabia became shaped by the hot and dry climate that we are familiar with, while in other parts of the world communities have adapted to – and become dependent upon – climates that are very different.

Nowhere is this more true than in northern India, where about 600 million people live in areas where monsoon rains are essential to agriculture. Without them, the mode of life in this region would alter dramatically.

The importance of these annual rains has been brought into sharp focus by a study by New York University Abu Dhabi (NYUAD) researchers.

Their modelling has indicated that climate change will cause low-pressure systems (LPSs) that create the Indian monsoon rains to shift northwards. The resulting reduction in rainfall that some areas will experience could have a major impact on agriculture.

What is more, the same human-generated upheavals that are set to affect weather patterns in India could influence the climate in parts of Arabia.

A key resource to the researchers, whose study was published recently in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), has been India’s impressive database of weather records.

The country has reliable data about its weather going back to at least 1900, and this has proved useful for identifying patterns of change and testing models of how the climate may alter in the future.

Using the observational data and combining it with a complex system of mathematical modelling, the researchers forecast that, by the end of this century, overall monsoon synoptic activity (weather systems that last a few to several days and span a few hundred to a few thousand kilometres) will have decreased 45 per cent. There is also a slight northward shift in the winds that create the monsoons.

“We found there’s a very drastic decrease in the low-pressure systems,” said Dr Ajaya Ravindran, a senior scientist in NYU Abu Dhabi’s Centre for Prototype Climate Modelling and one of the study’s authors.

“There’s a decline in the seasonal mean precipitation and a shift towards the foothills of the Himalayas.”

Abu Dhabi, UAE, April 4, 2018. Dr Ajaya Ravindran. Feature on work at NYU Abu Dhabi on monsoons and how they will be affected by climate change. Victor Besa / The National National
Dr Ajaya Ravindran pictured at NYU Abu Dhabi. Victor Besa / The National

There was a 10 per cent forecast increase in the number of low-pressure systems that develop over land, but much larger reduction in the number developing over water, which results in an overall decline.

Dr Ravindran emphasises that the results of the study should be treated with caution because they are the product of only one model.

Typically when it comes to forecasting how climate change will affect weather patterns, the results of multiple models are compared and an average, called the ensemble mean, generated.

“You take at least 10 models from different agencies; every model should simulate the same scenario,” said Dr Ravindran.

Yet previously published models have forecast a similar effect and these latest results tie in with observational data indicating that a reduction in average seasonal rainfall has already happened.

“We have already found from observations that the rainfall in Kerala and southern places is decreasing. This will further reinstate that drying,” said Dr Ravindran.

What sets the NYU Abu Dhabi research apart from many previous attempts to forecast how climate change will affect particular areas is its level of detail.

It uses a High Resolution Atmospheric Model (HiRAM), developed by researchers at the Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, United States, with horizontal grid spaces of 50km, which offers more precision than many other models, which are often global and based on much lower resolution.

“Quite a lot of computing [power] is needed for that [50km model],” said Dr Ravindran.

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As is typically the case with climate change, the effects are not consistent and will vary from one place to another. There are areas even in southern India that will have more rainfall, even if the average rainfall in the region overall is likely to decline.

“There are areas with more rainfall and some with less rainfall. That will disturb the human settlements, but exact prediction, it’s very difficult,” said Dr Ravindran.

The significant effects that a loss of monsoon rains can have are vividly illustrated by a look back into the history of Arabia.

A 2015 study indicated that every 23,000 years or so there were wet phases in the Arabian peninsula that saw monsoon rains penetrate into the interior, creating a lush habitat. When the monsoons disappeared, so did this habitat. Only a small edge of Arabia currently experiences the remnants of this monsoon, such as the area around Salalah in Oman, which enjoys a lush summer climate during the khareef monsoon season.

Dr Ravindran is keen to emphasise that the changes his model forecasts will not cause currently lush areas of India to become desert. But they could have a significant impact on the agriculture that becomes possible in the affected areas.

“We want to extend it … and look into details of what happens to precipitation on a local scale, and how much it reduces and where it reduces,” said Dr Ravindran.

The other authors of the study, which is entitled Decline and poleward shift in Indian summer monsoon synoptic activity in a warming climate, include Dr Sandeep Sukumaran, a research scientist at NYU Abu Dhabi’s Centre for Prototype Climate Modelling, Dr V. Praveen, a senior support scientist at the centre, and Dr TP Sabin, who has worked at NYU Abu Dhabi and is now based at the Centre for Climate Change Research of the Indian Institute of Tropical Meteorology in Pune, India. The Department of Earth and Planetary Science at the University of California, Berkeley, also contributed to the research.

Having analysed in-depth the way that climate change could affect the pattern of low-pressure systems in India, the researchers at NYU Abu Dhabi are now turning their attention to the climatic upheavals that the Arabian peninsula can expect.

Given that some parts of India will be facing major changes in their climate, many people in Arabia will no doubt be keen to learn about what their part of the world too will be facing.