The southwest monsoon is set to intensify across large parts of India over the next few days as a depression over the northwest Bay of Bengal strengthens, prompting the India Meteorological Department (IMD) to issue heavy rainfall alerts for more than 10 states.

The weather system is expected to bring heavy to extremely heavy rainfall across eastern, central, western and northern India, increasing the risk of floods, landslides and waterlogging. The fresh spell of rain comes at a time when several states are already dealing with the impacts of an active monsoon, making them more vulnerable to further weather-related disasters.

Bay of Bengal Depression to Strengthen Monsoon

According to the IMD, a low-pressure area over the northwest Bay of Bengal and adjoining Odisha–West Bengal coast is likely to intensify into a depression before moving west-northwest across Odisha, Chhattisgarh and central India.

A depression is a well-organised low-pressure weather system that forms over warm ocean waters. During the southwest monsoon, the Bay of Bengal is the primary region where these systems develop. As they move inland, they transport large amounts of moisture from the sea, producing widespread rainfall over several states. Although weaker than cyclones, monsoon depressions are among the most important drivers of India’s seasonal rainfall.

The IMD has forecast isolated extremely heavy rainfall over Odisha and Chhattisgarh, while heavy to very heavy rainfall is expected across parts of Madhya Pradesh, Maharashtra, Gujarat, Rajasthan, Uttar Pradesh, Uttarakhand, Himachal Pradesh, Gangetic West Bengal, Konkan and Goa. Widespread rainfall is also likely across the northeastern states, including Assam, Meghalaya, Arunachal Pradesh, Nagaland, Manipur, Mizoram and Tripura.

Fresh Rain Could Worsen Existing Floods

The latest depression arrives after several weeks of intense monsoon activity across the country. States such as Himachal Pradesh and Uttarakhand have witnessed recurring landslides and flash floods, while Assam has experienced repeated flooding as the Brahmaputra and its tributaries swelled following continuous rainfall. Parts of Gujarat, Maharashtra and central India have also reported flooding and waterlogging after successive spells of heavy rain.

Meteorologists say the concern is not only the amount of rain expected but also where it will fall. Much of the landscape in these regions has already become saturated, reducing its ability to absorb additional rainfall.

When soil reaches its storage capacity, fresh rainfall flows directly into streams and rivers instead of soaking into the ground. This increases surface runoff, causing rivers to rise more rapidly and raising the risk of flash floods and urban flooding. In hilly regions, continuous rainfall also weakens slopes, making landslides more likely.

Growth of Climate Challenge

Scientists increasingly describe situations like these as compound weather events, where one weather event amplifies the impact of another. A fresh spell of heavy rain falling over flood-affected areas can prolong flooding, delay recovery and increase damage to homes, roads and public infrastructure.

Climate change is expected to make these risks more pronounced. According to the Intergovernmental Panel on Climate Change (IPCC), the atmosphere can hold about 7% more moisture for every 1°C rise in temperature, increasing the potential for intense rainfall during monsoon weather systems. Studies by the India Meteorological Department and the Indian Institute of Tropical Meteorology have also reported an increase in short-duration extreme rainfall events across parts of India over recent decades.

Authorities Urge Vigilance

The IMD has advised residents in flood- and landslide-prone areas to closely monitor weather updates and follow local advisories. Fishermen have been warned against venturing into the Bay of Bengal and adjoining parts of the Arabian Sea due to rough sea conditions.

State disaster management agencies are also monitoring river levels, reservoir inflows and vulnerable districts as the depression moves inland.

While the active monsoon is expected to replenish reservoirs and support the ongoing kharif cropping season, the latest depression highlights the growing challenge of managing consecutive extreme rainfall events. For communities already affected by floods and landslides, the coming days will test the resilience of infrastructure, disaster response systems and local preparedness as another round of heavy rain sweeps across the country.

As the world marks the International Day for the Conservation of the Mangrove Ecosystem, Mumbai mangroves tell a story of survival, climate resilience, and lessons learned from the devastating 2005 floods. From Thane Creek to the Mithi River, these coastal forests reduce flood risk, store carbon, support marine biodiversity, and sustain millions of livelihoods. Yet despite legal safeguards and restoration efforts, pollution, infrastructure projects, and climate change continue to threaten one of India’s most valuable natural defences.

“This is Avicennia marina,” said Manish Zendeker, pointing to the trees lining the water as he steered his ferry through the narrow channels of the Thane Creek Flamingo Sanctuary. “In total, 17 species are found in Maharashtra. Overall, they are called mangroves, but among them, this is a distinct species. We see this more commonly here in Mumbai. If you go towards Ratnagiri, you will mostly see Sonneratia alba.” He went on, unprompted, into the mechanics of why the species in front of us mattered: “Its presence here is so important because it works to filter the creek water — it purifies it. Its roots go underwater and come back up, which are called pneumatophores, or breathing roots. Those roots have many tiny pores. When the high tide water comes in, their pores open up and absorb whatever pollution or chemicals are in the water. So that is its main benefit — it works to keep the creek water clean.”

What surprised our reporting team wasn’t that a boat driver on Thane Creek knew mangroves mattered — most people who live near them can tell you that much. It was the precision: a species name offered without hesitation, a north-south distinction between what grows here and what grows 300 kilometres south near Ratnagiri, a working theory of how the roots do their job, delivered from memory, between turns of the outboard motor. It was the kind of knowledge that usually lives in a research paper.

Today, 26 July, is the International Day for the Conservation of the Mangrove Ecosystem, a date the United Nations chose deliberately: it marks the anniversary of the 2005 Mumbai deluge, the day 944 millimetres of rain fell on the city in 24 hours and more than a thousand people died. The date is not a coincidence, and neither is the connection to Mumbai. What happened that day, and what has happened in the two decades since, is one of the clearest real-world demonstrations anywhere of what a mangrove forest is actually worth — and what a city pays when it disappears.

How mumbai mangroves protect the city from floods

By the time the 2005 floods hit, Mumbai had already spent roughly a decade quietly getting rid of its mangroves. Between the early 1990s and 2005, the city lost close to 40% of its mangrove cover — something in the range of 9,000 acres — much of it along the Mithi River, where the swampy, root-tangled land was drained and filled to build what is now the Bandra Kurla Complex, one of the city’s premier commercial districts. The Mithi itself, an 18-kilometre stormwater channel that carries overflow from Powai and Vihar lakes out to the Arabian Sea, had been narrowed, built over, and used for decades as an open drain for sewage and industrial waste.

When the rain came, the river had nowhere to put it. A 2018 hydrological case study of the Mithi River modelled what the mangrove loss actually cost the city in physical terms: intact mangrove forest along the riverbanks reduces flood wave height and cuts the inundation area by roughly 21%, by absorbing and slowing the surge before it reaches built-up land. Without that buffer, the 2005 floodwaters had nowhere to go but into the shops, homes, and railway lines of central Mumbai.

The flood changed the law almost immediately. Later that year, the Bombay High Court banned the destruction of mangroves on government land across Maharashtra and prohibited construction within 50 metres of any mangrove area, and by 2012 the state had set up a dedicated Mangrove Cell to enforce it. The reversal that followed is one of the more striking examples of legal protection actually working at scale: according to Forest Survey of India data, Mumbai’s own mangrove cover grew from 42 square kilometres in 2005 to 66 square kilometres by 2017, a 57% recovery. State-wide, Maharashtra’s mangrove cover more than kept pace, expanding from 186 square kilometres in 2013 to 320 square kilometres by 2019, according to the Mangrove Cell’s own figures.

That recovery is real, but it is not the whole story, and it is not evenly spread. Forest officials themselves have cautioned that a rising area figure can mask falling ecological quality — mangroves can be denser or thinner, healthier or stressed, without that showing up in a simple hectare count. And the growth has come alongside continuing, highly localised battles: mangrove clearance tied to the Navi Mumbai International Airport, the Jawaharlal Nehru Port Trust’s expansion, and the Mumbai Trans-Harbour Link have repeatedly ended up in court, with activists and the state’s own Mangrove Cell frequently on opposite sides of the same case. Nationally, the trend has also turned again: India lost an estimated 7.43 square kilometres of mangrove cover just since 2021, though that recent decline is concentrated in Gujarat and the Andaman and Nicobar Islands rather than in Mumbai itself. The net picture for the city is a genuine recovery, won directly by an emergency response to a specific disaster, that now has to be actively defended patch by patch rather than assumed to hold on its own.

The comparison that made the point hardest to argue with came from a single village. Nandakumar Pawar, a fisherman in Bhandup, a mangrove-fringed suburb in Mumbai’s north-east, has described being startled that his neighbourhood came through the 2005 deluge largely unscathed while the rest of the city drowned. A more than 800-hectare stretch of mangroves near his village had acted as exactly what mangroves are built to be — a sponge, absorbing the surge rather than passing it on to the houses behind it. Pawar went on to found Shree Ekvira Aai Pratishthan, a fishing-community organisation that today serves as caretaker of some 1,042 hectares of mangrove forest between Mulund and Vikhroli along Thane Creek, working with the state Forest Department on protection and restoration. Pawar, now in his sixties, also serves as president of the Maharashtra Small-Scale Traditional Fish Workers Union — one measure of how directly a single flood turned a fisherman into one of the city’s more persistent mangrove advocates.

Thane Creek: a working case study

The waters our reporting team travelled — Thane Creek, Asia’s largest creek at 26 kilometres long — offer a live, ongoing version of this story rather than a historical one. The northern stretch of the creek was declared a flamingo sanctuary in 2015, protecting 1,690 hectares, of which 896 hectares are mangrove forest and the rest open water and mudflats. The creek has drawn over 30,000 migratory flamingos annually since the early 1990s, and by some counts accounts for close to a fifth of the mangrove species diversity found anywhere in India.

It is also a case study in what happens when mangroves are stressed rather than removed outright. Untreated sewage, industrial effluent, and construction runoff have degraded water quality across large stretches of the creek; one WWF-India assessment found that 58 of 69 marine species once recorded there have disappeared over a 14-year period, largely attributed to rising arsenic levels and falling oxygen content in the water. The sanctuary’s own mangroves have been the subject of repeated pollution complaints, including an industrial pipeline leak flagged by local fishermen in 2022. The lesson embedded in Thane Creek is that mangrove protection on paper — a sanctuary notification, a protected-area boundary — does not by itself guarantee a functioning ecosystem; the water quality and the tree cover have to be defended separately and continuously.

Restoration work has had some success. Community-led projects around Thane Creek and Mahim Bay have restored more than 100 hectares of mangrove cover in recent years, working with local fishing communities to combine habitat recovery with sustainable fishing practices and small-scale eco-tourism — the same boat tours that carried our reporting team through the sanctuary.

What the research says mangroves are worth, everywhere

Mumbai’s experience is a local instance of a pattern researchers have now quantified at a global scale, and the numbers are large enough to change how governments plan coastal defence.

A widely cited 2020 study published in Scientific Reports, led by researchers Pelayo Menéndez and Michael Beck, modelled the flood-protection value of every mangrove forest on Earth at 20-kilometre resolution and found that mangroves currently prevent more than US$65 billion in flood damage every year, and protect over 15 million people from flooding they would otherwise experience. A follow-up analysis, published in the World Bank’s Changing Wealth of Nations 2024 report, priced the total long-term value of that protection — the present value of a century of avoided flood damage — at US$855 billion globally. The countries that benefit most in absolute terms include China, Vietnam, the United States, Australia, and India; in terms of the sheer number of people protected, Vietnam, India, and Bangladesh top the list.

Mangroves do this largely through friction. Their dense, tangled root systems and low canopy break up wave energy and slow storm surge as it moves inland; the State of the World’s Mangroves 2024 assessment estimates that mangrove forests reduce flood depth by 15–20% compared with a coastline that has none.

The carbon case is, if anything, stronger. Mangrove soil is waterlogged and largely oxygen-free, which means the organic matter that collects in it barely decomposes — it simply stays there, sometimes for thousands of years. Researchers estimate mangroves store an average of 394 tonnes of carbon per hectare, split roughly 78% in the soil, 15% in above-ground biomass, and the rest below ground, figures that vary sharply by region: forests in Southeast Asia and the Philippines can exceed 650 tonnes per hectare, while carbon density in parts of the Middle East falls below 100. Even though mangroves cover under 1% of the world’s tropical forest area, one estimate puts their total global carbon stock at around 6.5 billion tonnes — the single largest carbon pool of any blue carbon ecosystem, ahead of seagrass meadows and salt marshes combined in density per hectare, if not in total area.

None of this is guaranteed to last. The global rate of mangrove loss has slowed — from roughly 1% a year in the 1990s to about 0.66% a year between 2010 and 2020, and the FAO’s 2025 Global Forest Resources Assessment even found a net global gain since 2010, reversing decades of decline — but a 2024 assessment by the International Union for Conservation of Nature found that more than half of the world’s mangrove ecosystem types are still at risk of collapse by 2050 if current pressures continue, a category that includes South India’s mangroves specifically, which the IUCN has already classified as critically endangered. Area recovering is not the same as risk disappearing; it mainly means the fight has shifted from outright clearance to slower, harder-to-see pressures — pollution, aquaculture expansion, and the kind of localised infrastructure disputes already playing out around Mumbai.

Governments have started responding at the scale the research implies is necessary. At COP28 in 2023, the Mangrove Breakthrough initiative set a global target of restoring or protecting 15 million hectares of mangrove forest by 2030, backed by a proposed US$4 billion in financing — an explicit bet that the cost of restoration is small next to the avoided cost of flooding, storm damage, and lost carbon storage that follows when mangroves disappear.

What the boat driver already knew

None of this would have surprised the man steering the boat through Thane Creek. Long before any of these studies were published, people who live beside mangrove forests — fishermen in Bhandup, boat operators on the creek, families along the Mithi’s banks — had already worked out, through direct experience, what the data now confirms with figures: that the trees standing between them and the water were doing something that mattered, long before anyone put a price on it.

Mumbai’s flood risk has not gone away since 2005, even though its mangrove cover has, on paper, come back. Sea levels are rising, monsoon rainfall is becoming more erratic and more intense, and the city’s population and built footprint keep expanding into the same low-lying, once-swampy land that used to absorb the water. The mangroves that have grown back — in Thane Creek, along Mahim Bay, in the restored patches near the Mithi — are doing exactly the job the research describes: quietly absorbing surge, filtering pollutants, and storing carbon. Whether they keep doing it depends less on whether the trees are allowed to grow than on whether anyone keeps watching, largely unnoticed, until the next storm makes their condition impossible to ignore.

Nearly every global coral bleaching event over the past four decades would not have occurred without human-caused climate change, according to a new study published in Oceanography. Researchers found that while El Niño can intensify ocean warming, fossil fuel-driven climate change has been the decisive factor behind mass bleaching events since 1998. The findings suggest rising global temperatures—not natural climate variability—are now the dominant threat to coral reefs and the millions of people who depend on them.

Nearly every mass coral bleaching event of the past four decades would not have happened without human-caused climate change, according to new research published in the journal Oceanography — a finding that upends the common assumption that El Niño is the primary trigger behind the world’s worst reef die-offs.

The study, led by Climate Central, examined the four global bleaching events recorded since 1998 — in 1998, 2010, 2014–2017, and 2018–2025 — periods that have typically been associated with El Niño’s warming influence on the Pacific Ocean. Researchers found that fossil fuel-driven ocean heat, not the natural climate cycle, was the fundamental force behind the bleaching and coral mortality in each case.

Climate Change Is Driving Global Coral Bleaching,

Scientists used a multi-model extreme event attribution method — a technique that isolates how much of an observed climate event can be traced to human-caused warming versus natural variability — to assess climate change’s influence on sea surface temperatures. They then layered those results onto the coral bleaching risk model developed by NOAA’s Coral Reef Watch program to calculate how much of the observed bleaching risk was attributable to each factor.

The results were stark for the most recent and most severe event. During the 2018–2025 bleaching event, the analysis found there would have been essentially no coral bleaching — and certainly no global-scale event — in a world without human-caused climate change. Of the 71 regions where bleaching was observed during that period, only one would have faced even a moderate bleaching risk absent climate change. Researchers found similar results across all of the other three global events: in each case, climate change was necessary to push ocean temperatures over the threshold at which bleaching occurs.

“Our study shows that without climate change, coral bleaching would be a rare and isolated event, and global mass coral bleaching simply would not occur,” said Andrew Pershing, Chief Program Officer at Climate Central and the study’s lead author. “Millions of people and entire countries rely on healthy coral reefs for livelihoods and food security. But our emissions of carbon pollution are causing increasingly widespread damage and death to these vital and vibrant ecosystems. Without immediate emissions reduction, coral reefs as we know them will disappear.”

What it means for the El Niño underway now

Using the same methodology, the researchers also modeled bleaching risk for the El Niño event currently underway, which began in 2026. They project that while natural El Niño-driven warming could produce low levels of bleaching risk in a handful of regions, human-caused climate change is likely to drive bleaching more broadly across the globe — with the southern Caribbean, the Central and South American coasts, and the coasts of eastern Asia identified as particular hotspots.

The researchers argue the finding matters because public discussion of bleaching events tends to focus on El Niño rather than the underlying warming trend. That framing, they say, is likely to become increasingly inaccurate: under current warming rates, the study concludes that rising temperatures driven by human-caused climate change will outweigh El Niño’s contribution in every coral-containing region on Earth by 2028.

A narrowing window for reefs already under strain

The paper adds to a growing body of evidence that coral reefs, despite some documented capacity to adapt to warmer conditions, remain at escalating risk. Absent a reduction in carbon emissions, the study’s authors conclude, continued ocean warming raises the likelihood that reef ecosystems as they currently exist could disappear permanently.

Coral reefs cover a small fraction of the ocean floor but support an outsized share of marine life, and provide fisheries, coastal protection, and tourism revenue that hundreds of millions of people depend on directly.