When we talk about climate change impacts, the word that’s often used is “unprecedented”, that which can’t be measured by any given yardstick. Something unprecedented happened over the Western Ghats between 19-25 July. For about a week, a large section of the range, especially in Maharashtra, was deluged under a nearly never-ending barrage of extremely heavy rainfall that grew progressively more intense with each passing day.
It started with a low pressure area forming over the Bay of Bengal in mid-July. A common enough occurrence during the monsoon months of June to September, this low pressure area acted as an anchor for rain-bearing westerly winds from the Arabian Sea, which began flowing towards the trough. These winds were laden with high amounts of moisture from an overheated Arabian Sea where the sea surface temperatures at the time were 1-2 degrees Celsius above normal. As these winds rushed towards the low pressure area, they encountered the high range of the Western Ghats. And they dumped all their water.
Between 19-21 July, the amount of daily precipitation increased from 98mm on the 19th, to 110mm on the 20th and then 164mm on the 21st. Such large amounts of daily rainfall would have anyway qualified as an extremely heavy rainfall event. But worse was to come. On 22 July, the area received rains of 480mm. And on 23 July, 594mm of rain was dumped over the Western Ghats. This had become an extreme rainfall event, with cataclysmic results.
As of 25 July, at least 112 people have been killed and 99 people remain missing. Across nine districts in Maharashtra, some 890 villages were badly affected. The worst calamities befell people living in the plains at the western foot of the Ghats, in the state’s Raigad, Ratnagiri and Sindhudurg districts. At least 42 people were killed in Raigad’s Taliye village, where a part of a local hillock collapsed in a landslide, burying over 30 houses. As rivers swelled and dams were filled to capacity and rain run-off washed down to the plains from the Ghats, cities like Chiplun in Ratnagiri were swept up in massive floods, with the water level rising high enough to inundate even the first floors of buildings. This was record rainfall. Mahabaleshwar’s previous daily precipitation record was in August 2008, when it saw rains of 497mm. People simply hadn’t experienced continuous rainfall like this in generations, with an earlier record of 439mm registered way back in 1977. Again, that word, unprecedented.
It’s just that in this era of climate change, monsoon calamities like this are no longer uncommon. Something very similar happened in Kerala in early August 2018, when days of extreme rainfall caused widespread devastation in the state, resulting in floods and landslides. Nearly 500 people lost their lives and the state government estimated damages caused by the floods to be to the tune of ₹20,000 crore. According to a report prepared by the Central Water Commission, between 1-13 August that year, Kerala received rainfall that was 164% above normal. Rainfall on 9 August, that triggered the floods, ranged between 214-398mm across four districts. It was the worst case of flooding that Kerala had experienced since 1924. Unprecedented indeed.
An unpredictable force
Climate 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.
The country’s first ever official climate change report, the Assessment Of Climate Change Over The Indian Region, prepared by the Indian scientific community and published by the ministry of earth sciences (MoES) in 2020, lays out the state of the monsoon in a rapidly heating world quite clearly. Since 1951, the monsoon circulation has weakened, especially in regions like the Western Ghats and the Indo-Gangetic plains. Simultaneously, however, incidents of localised heavy rainfall have increased. What has also increased is the duration of dry spells between rainy days during the monsoon.
Climate scientist Madhavan Rajeevan who is also secretary, MoES, has studied the Indian monsoon for decades. He is also one of the expert reviewers of the assessment report. Speaking to Lounge, he clarifies that 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.
According to the India Meteorological Department (IMD), daily rainfall of 2.5mm or above is considered a rainy day. Single day rainfall of 124.5mm to 244.4mm is considered very heavy rain, and anything above that is considered extremely heavy rain. The assessment report states that as compared to 1901-1975, rainfall has reduced by 1-5mm/day during 1976-2015 over central India, Kerala and some parts of north-east India. The frequency of dry spells has increased by 27% between 1981-2011, as compared to 1951-1980. The intensity of wet spells has also gone up in recent decades.
Climate models indicate that global warming is expected to increase monsoon rainfall by 14% by the end of the century if greenhouse gas (GHG) emissions remain high (see graphic). In the medium emissions scenario, monsoon rainfall may increase by 10%.
“This is primarily due to the rise in the moisture content in the atmosphere,” says climate scientist Roxy Mathew Koll of the Indian Institute of Tropical Meteorology (IITM) Pune, referring to effects of higher temperature on monsoon rains. 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.
He adds that 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.
This is the exact trend that Koll and other scientists, including Rajeevan, recorded in a 2017 paper called A Threefold Rise In Widespread Extreme Rain Events Over Central India, published in Nature. The study states that despite a weakening in overall monsoon circulation, extreme rain events over central India have increased threefold between 1950-2015. The scientists found that this was due to the rising unpredictability of monsoon westerly winds from the Arabian Sea, which was “driving surges of moisture supply, leading to extreme rainfall episodes across the entire central subcontinent.” Studies such as this make it abundantly clear that the effects of climate change are already here, and not just a future challenge for India to grapple with.
Records from deep time
By the late 19th century, meteorology, or the study of atmospheric phenomena, was a fairly well established, if young, science. Driven by the invention of the telegraph, an international arena of climate and weather observations had emerged, and this was formalised in 1873 by the creation of the International Meteorological Organization (IMO). National weather services of the United States and European imperial powers like Britain started sharing information under its auspices. Classification of clouds, their names and types, which had begun to be studied since the early part of the century, became standardised. This was further enhanced by the advent of photography. The IMO published a first illustrated cloud atlas in 1892.
For the British colonial government of India, understanding the country’s climate became a matter of paramount importance following a series of weather cataclysms, most notably the Calcutta cyclone of 1864, and a failure of the monsoon and the subsequent famine of 1876-78. The India Meteorological Office, the precursor to the modern IMD, was founded in 1875 with meteorologist Henry Francis Blanford as its director. By 1880, there were over 100 meteorological observation stations across the country, and in 1882, Blanford felt emboldened enough by his understanding of the monsoon, to start issuing forecasts. Primarily based on Himalayan snowfall patterns, these annual monsoon forecasts were institutionalised in 1885, with the Gazette Of India publishing them from that year onward.
The veracity of these broad-brush forecasts were upended by the the drought and famine of 1896, followed by a monsoon-triggered malaria epidemic in 1897. It was a terrible few years for India, ravaged as it also was by a bubonic plague epidemic in 1896. It was clear that although Blanford and other meteorologists of the day had grasped the basic form and workings of the monsoon, driven by, as Blanford wrote in his 1877 book Meteorology In India, “(the) primary contrast of land and water”, they still saw the monsoon as a “secluded and independent area of atmospheric action.”
In 2021, we know better. The Indian south-west monsoon, despite its hyper-localised effect on the Indian subcontinent and Indian Ocean Asia, both influences and is influenced by global factors. The meteorologists of the 19th century wouldn’t have known about the El Niño weather phenomenon over the Pacific Ocean, and how it influenced the droughts of the late 19th century. Or how changes in wind circulation over the Atlantic and north Pacific Oceans can influence monsoon variability in India. They would certainly not have known about the effects of high CO2 concentrations in the atmosphere, nor about how planetary warming affects the monsoon.
While climate scientists are broadly clear about the present and future effects of high emissions on the Indian monsoon, there is always room for more proof, better data. This is what drove an international scientific team led by Steven Clemens, a professor of earth sciences at Brown University in the US, to delve into the past of the Indian monsoon to provide some insight about its future.
They sailed to the Bay of Bengal in late 2014 on a research vessel, the JOIDES Resolution, in order to drill several kilometers of sediment core samples from three points beneath the sea-floor of the Bay. The team collected samples from the Bay of Bengal continental margin, near the mouth of the Mahanadi delta, as well as from the Andaman Sea near the mouth of the Irrawaddy. Clemens and his colleagues were hoping to re-construct how the Indian monsoon had behaved, in terms of rainfall intensity, through the late Pleistocene era (about 1.5 million years ago). The study involved various analyses, like the oxygen isotopic composition of fossil microorganisms called planktonic foraminifera, the rubidium concentrations in sediments brought in by river runoff, and the carbon isotopic composition of plant matter washed into the sea and buried in the sea-bed.
These various analyses reflect the state of the monsoonal environment in which the microorganisms and the plants existed and how the environment changed through time. Changes in the isotopic composition of foraminifera reflect changes in water salinity , changes in vegetation isotopes gave an indication of changes in vegetation type, reflecting temperature and rainfall amounts, and changes in rubidium reflect changes in sediment input from river runoff. This deep dive into the monsoon’s past yielded results in June of this year, when their paper, Remote And Local Drivers Of Pleistocene South Asian Summer Monsoon Precipitation: A Test For Future Predictions, was published in the journal Science Advances.
The study illustrates that 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,” Clemens said at the time of the release of the report.
Monsoon rainfall changes of the Pleistocene occurred due to natural changes in atmospheric CO2 levels and took place over very long periods of time. Today, human CO2 emissions are changing the Earth’s climate at a much faster pace. But if humans are changing the atmospheric CO2 content so fast, is the climate changing rapidly as well? The answer, Clemens says, speaking to Lounge, lies in the depths of the ocean. “We’re changing the CO2 content of the atmosphere about 40 times faster than it changed under natural conditions. And the question is why hasn’t climate changed in proportion to that? The answer is that humans live at the interface between the land surface and the atmosphere, whereas most of the energy from the increases in CO2 is going into the intermediary depths of the ocean, mostly being hidden from us.”
It’s only now that the effects of that absorbed energy is beginning to be seen in the atmosphere. Clemens says that ocean waters circulate at multi-decadal and centennial timescales. The atmosphere, on the other hand, circulates on semi-annual timescales. “There’s a lag between when you inject CO2 into the atmosphere, and when you start seeing the longer-term effects of that in the climate system,” he says, adding, “I think we are just now beginning to experience the impacts at an accelerated rate.”
When the levee breaks
What makes the Indian monsoon such an object of fascination, when it’s just one monsoon system among many? For climate scientists, the answer is quite straightforward. “The Indian monsoon is really interesting because it is one of the largest mechanisms by which tremendous amounts of energy are moved between hemispheres. You don’t get any bigger tropical climate signals than the Indian monsoon.” says Clemens.
This “energy transfer” from the southern to the northern hemisphere occurs when an equatorial band of tropical, heavy rainfall, the Inter-Tropical Convergence Zone (ITCZ), migrates north from the southern Indian Ocean to the northern Indian Ocean. As it does so, it starts raining over the Bay of Bengal between late-April and mid-May. It moves further north, bringing rainfall in the northern reaches of the Bay between mid-May and mid-June. The rainfall begins over land around 1 June, in Kerala.
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According to some studies, the moisture from the southern Indian Ocean contributes to anything between 46%-55% of the monsoon rainfall over India. A study released in January this year, Zonally Contrasting Shifts Of The Tropical Rain Belt In Response To Climate Change, published in the journal Nature, states that climate change may be affecting the ITCZ itself. The study states that as the northern hemisphere heats up faster than the southern hemisphere due to melting Arctic and Himalayan ice and snow, the ITCZ may be slowly shifting north from its current position near the equator. This would intensify flooding in southern India by the end of the century.
As it is, India is one of the most flood-prone regions in the world. A 2012 Consortium of International Agricultural Research Centers (CGIAR) report on global flood hot spots identified India as the country that suffered the most flood events between 1900-2011. A 2020 report from the United Nations Office for Disaster Risk Reduction (UNDRR) called The Human Cost Of Disasters: An Overview Of The Last 20 Years (2000-2019) found that much of the increase in climate-related disasters occurred due to major flooding events and storms. India featured prominently in the report, as the country with the third highest number of disaster events (321) in the past 20 years. India was also the second most impacted country by floods, after China, with an average of 17 flood events per year and approximately 345 million people affected.
“We call it the flood season, not the monsoon season. It is a given that by the first or second week of August, we will start having floods,” says Eklavya Prasad of Megh Pyne Abhiyan, a Delhi-based NGO working on water issues in north Bihar, Jharkhand and West Bengal. Bihar is one of the most flood prone states in the country. This is due to a combination of factors, including the fact that no fewer than four Himalayan rivers, all tributaries of the Ganga, flow through the state. The main ones, like the Gandak and especially the Kosi, carry an immense amount of Himalayan sediments as well, and come monsoon rains, they swell up and flood.
“If you look at government data from the last 20 years, there hasn’t been a single year that we have not had floods. There are about 11 districts that have faced floods in more than 15 of the last 20 years. Among these, some districts like Supaul have had floods every year,” says Prasad. Since the creation of Jharkhand in 2000, the total flood-prone area of present-day Bihar amounts to 73.63% of its total geographic area. But if flooding in Bihar is a regular occurrence, what has changed is the nature of those floods, says Prasad. And the reason for that is the creation of river embankments in an effort to “control” floods.
River embankments have a long and convoluted history in India. The British experimented with them in an effort to control free-willed Indian rivers, but after a while, the colonial government seemed to give up on the idea. It resurfaced in independent India in the wake of the Kosi floods of 1953-54. The Union government responded to it by signing a treaty with Nepal and undertaking a massive programme of building embankments along the river, the main channel of which rises in the shadow of Mt Everest. Once this was completed in 1959, through the subsequent decades, embankments became something of a panacea for Indian policy-makers, who, despite enough evidence to the contrary, continue to believe that this is the best way to control floods, especially in states like Bihar and Assam. Today, Bihar alone has 3,790km of embankments.
“Once upon a time, flooding used to be something of a uniform phenomena in north Bihar. But then the floodscape changed based on flood control interventions, the creation of embankments. So the rivers, which at one point of time used to spread out when in spate and then narrow down to a normal flow, stopped behaving that way,” says Prasad. The Himalayan and other sediments carried down by rivers like the Kosi earlier used to spread out with the flood waters, depositing rich silt on the plains, acting as an agricultural boost. Squeezed by embankments, the sediments now have nowhere to go, thus raising the height of the river bed. This forces the government to raise the height of the embankment. A vicious cycle ensues, and when embankments breach, the results are catastrophic.
The 2007 Bihar floods are a pertinent case in point, one of the worst cataclysms in living memory where 1,287 people were killed across 19 districts due to a combination of extremely heavy monsoon rainfall, overwhelmed dams and breached embankments. The following year, a single breach in the Kosi embankment in the village of Kusaha in Nepal’s Sunsari district, just 5km from the Bihar border, led to another devastating flood as the Kosi, freed from its constraints, violently changed its course. A 2019 report by the Bihar water resources department says that between 1987-2018, there were 408 breaches in embankments by different rivers in the state.
Prasad says in the past few years, the flood season is beginning earlier each year. “It is important to understand this as well, that floods come in cycles. Last year, when we were done with the first phase of floods back in July; and it again rained again around the 23rd, 24th of September bringing in another cycle of floods.”
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He adds that flash floods caused by heavy rains are as much of a concern, as they can occur any time, not just during the monsoon. “Embankments are not saving lives, it’s the breach of the embankments that is causing more harm,” says Prasad, adding, “The government is kind of creating this whole fear that embankments are the only saviour and without embankments you are unsafe. At the end of it, one breach of the embankment devastates everything.”
Prasad fears that the government may end up just blaming climate change for every new flood event, rather than fixing existing defects in flood management. “What we have been talking about is that we should start looking at flood-resilient habitats. Now, that will only be successful if it’s done based on a knowledge of the typologies of flood that we have,” says Prasad. He believes that only a district-level clarity of this will enable the formulation of adaptation strategies on a sound basis.
Rapidly melting Himalayan glaciers add one more layer of risk to people living in the catchment areas of the Ganga and Brahmaputra river systems. As global temperatures rise, the Himalaya is heating up at a rate faster than the global average. At current rates of warming, by about 2050, there’s a high probability of regular, massive floods in Himalayan rivers, as rates of glacier discharge increase. This would be disastrous for some 848 million people who live in the Ganga and Brahmaputra basins.
Map, plan, forecast, manage
Prasad is hardly alone in highlighting the urgent need for India to prepare risk maps of vulnerable areas. In December 2020, the New Delhi-based energy research institution Council on Energy, Environment and Water (CEEW) released a study appraising the climate change-induced threats facing India. Preparing India for Extreme Climate Events: Mapping Hotspots and Response Mechanisms, a district-level profiling of extreme climate events in India, concludes that 75% of Indian districts are vulnerable to events such as cyclones, droughts, floods and heatwaves. Authored by Abinash Mohanty, a programme lead at CEEW focusing on risks and adaptation, the study is based on an extreme events catalogue prepared by the organisation, covering a time period of 1970-2019.
The study finds that the number of such events are increasing across India. While between 1970-2005, there were 250 extreme climate events, there were 310 such events between 2005-2019. The frequency of flood events have increased by nearly eight times in the past 50 years. On average, while about 19 districts experienced annual floods between 1970-2005, between 2005-2019, 55 districts experienced floods every year.
“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.”
When it comes to urban flooding, says Mohanty, the culprit is over-urbanisation. “Every region in India has its natural inland drainage system, which has now been blocked or encroached upon. So you don’t have a natural drainage. In Mumbai the floods should be happening because of coastal flooding due to sea-level rise. But so far the cause is basically heavy rainfall and the water can’t drain out. So the problem of floods is also due to flawed land use planning in a changing climate scenario.”
Mohanty says that CEEW is working on a high-resolution climate risk atlas , that would identify risks on a district level. He believes that the challenges created by climate change can be met only with a hyper-local understanding of risks. “What India really needs to do is identifying the compounding impacts and multiple hazards that are coming in. The identification part should be the first step. We are living in an age where heavy rainfall is regularly turning into floods, and depressions into cyclonic storms; these are now part of our daily lives, and India’s localised disaster management processes need to be strengthened to tackle these extremes.”
The research organization World Resources Institute (WRI) India is drafting the Mumbai Climate Action Plan as a consultant to the city municipal corporation’s environment department. The draft is slated to be ready by November this year. According to urban planner and architect Lubaina Rangwala, associate director at the WRI India’s Sustainable Cities Centre, who is involved in the project, urban risks need to be managed through a combination of granular data, inclusivity and a focus on nature-based solutions.
“People always get the urge to try to engineer their way out of trouble,” she says, adding that any processes that stress natural systems further are bound to fail. “One of the things that we do in most cities now is concretizing the river’s edge. Instead of that, what cities should do is to look at the floodplains of rivers as non-program spaces. So you literally just take your infrastructure off of the flood plain and you transform them into areas that are softer, that are just natural spaces that can absorb the ebbs and flows of the river.”
Rangwala says that a city like Mumbai needs to actively protect its green spaces, its mangroves, because they truly add to the city’s capacity for resilience. The fact that Mumbai is situated on an estuary should guide its planning. Siting infrastructure or housing in previously natural spaces would amount to courting disaster. “If a natural space gets flooded and then the water subsides, then it wouldn’t be a concern. The moment you put density in these areas that are already vulnerable, then you are creating a calamity.” Rangwala says that progressive land use protections, like Maharashtra recently declaring 9,800 hectares of mangroves as forest land, is the way forward.
As climate change alters the way in which the monsoon behaves, Rajeevan believes that the nature of forecasting by the IMD should also evolve. “There’s no quick solution. And also there are no unique solutions. We need to improve our observations. We need to really understand more physics (of how the monsoon behaves). We also need to improve the resolution of the (forecast) models. We need to see whether we can really put this climate change variability into the model in some way,” he says.
Rajeevan suggests when it comes to weather forecasts beyond the immediate next three days, a probabilistic forecast instead of a deterministic one could be the way forward. This means that for any given situation, IMD would run 30-40 different forecasts, calculate the variability between them and then arrive at the probability of the forecast. “We should tell the people what could be the uncertainty in the forecast so that they can have a Plan A and also a Plan B, maybe even a Plan C.”
Koll says that certain steps can be taken immediately for better preparedness. “We have data and information for us to prepare a map of those regions where the heavy rainfall events are increasing or have increased; the regions where floods have increased, regions where landslides are more frequent. We have this data and it is possible to prepare flood maps based on these different contributing factors. We can also project how this might change in the next 10-20 years, and then make a plan based on that. It’s not an impossible thing.”
The most urgent need of the hour, however, is for the world to drastically reduce emissions and decarbonise. “You know, a consortium of nations came together to enable us to accomplish this science and present our results. Now it’s fundamentally an issue that these same governments have to take up. They need to heed the results, and they need to respond and react appropriately,” says Clemens.
Since the beginning of recorded cultural expression in the Indian subcontinent, the monsoon in all its glory, majesty and life-giving power, has been celebrated. For thousands for years, it has been the defining face of nature’s might in the lives of Indians. As the dark clouds of climate change approach us, it’s of paramount importance that we retain that sense of awe. It might be that fear that saves us.