Sea Water intrusion due to over pumping & Sea water Ingression due to global warming.

 Sea water intrusion takes place when there is excess withdrawal of ground water near seashore & movement of sea water in sub-surface to the aquifer making the sweet water saline whereas sea water ingression or incursin takes place because of rise in sea level due to melting of ice in Antarctica,Noth pole on effect of global warming. There is an interesting & very important fact relating to relative position of seawater - fresh water in coastal region.The discovery of the theory dates back to 1888 -89.

This resulted in the derivation of the famous Ghyben- Herzberg relation named after its originators, which explains the distribution of two fluids of different densities (sea water & freshwater)under hydrostatic equilibrium.
The practical implication of this famous & fundamental theory on Sea water intrusion is that , if the fresh water table is depleted by one mtr The seawater- fresh water interface will rise by 40mtr.The process is not instantaneous .It is gradual.But it will occur sooner or latter.As a result all the ground water exploitation structures(dug well,Tubewell etc) in the vicinity ,hydraulically connected with the zone,Which used to yield fresh water will discharge saline water.

It is therefore advised not to deplete ground water through pumping near the seashore/ costal belt.

Like surface ingression of ocean, sub surface ingression also takes place when we exploit more ground water. Now we have restricted new tube wells in 242 blocks of Odisha specially in Puri, Kendrapada, Jajpur, Bhadrak, Jagatsinghpur, Balasore, Ganjam as saline water appears due to incursion of sea water in sub surface. It was once studied that if we do not check drilling of new bore well in Kolkata city, sea water will intrude below Writers building.

Ground water exploitation has caused sinking of ground in many places.Subsurface ingression of sea water is a common phenomena where beneficiary gets saline water instead of sweet water. Beijing is not the only place experiencing subsidence or sinking, as soil collapses into space created as groundwater is depleted, parts of Shanghai, Mexico City, and other cities are sinking, too. Sections of California’s Central Valley have dropped by a foot, and in some localized areas, by as much as 28 feet.

As regions and nations run short of water, Damania says, economic growth will decline and food prices will spike, raising the risk of violent conflict and waves of large migrations. Unrest in Yemen, which heavily taps into groundwater and which experienced water riots in 2009, is rooted in a water crisis. Experts say water scarcity also helped destabilize Syria and launch its civil war. Jordan, which relies on aquifers as its only source of water, is even more water-stressed now that more than a half-million Syrian refugees arrived.The most over-stressed is the Arabian Aquifer System, which supplies water to 60 million people in Saudi Arabia and Yemen. The Indus Basin aquifer in northwest India and Pakistan is the second-most threatened, and the Murzuk-Djado Basin in northern Africa the third.We observed land subsidence in Indonesia due to heavy ground water exploitation. The same phenomenon is now observed in Punjab due to ground water over extraction.Now cracks are observed on building walls due to sinking of land.

Punjab has the highest rate of groundwater exploitation and had on average withdrawn 28.2 million acre feet (MAF) water yearly during 2008-2013. However, the yearly average replenishment of water was only 18.9 MAF.

73% of Punjab’s irrigated area uses groundwater for irrigation, while only 27% uses surface water. The number of tubewells had gone up exponentially from 2 lakh in 1971 to 12.50 lakh in 2015-16, with 41% of these have water availability beyond the depth of 60 metres.

The breadbasket regions of India and Pakistan are rapidly depleting their under ground aquifers. In an interview, climatologist Sonali McDermid explains why this over exploitation, combined with global warming, is creating an urgent need to change local farming practices.

India and Pakistan are among the most heavily irrigated nations on earth, producing enough wheat, corn, and other crops to feed their combined populations of 1.5 billion. But in South Asia’s breadbasket, which includes the Punjab region, farmers have pumped water out of the ground so heedlessly for so long that scientists now estimate aquifers there could run dry by mid-century. 

Sonali McDermid, a climatologist at New York University, has been working to better understand this gathering threat and help find potential solutions. In an interview McDermid explains why India and Pakistan have the world’s most overburdened aquifers, describes how the scale of South Asian irrigation is so vast that it’s actually moderating temperature increases and altering the monsoon, and discusses why crop diversification is vital to mitigating the impacts of climate change.

You are going to have to plant multiple crops in case you lose one,” says McDermid. “Farmers will need to experiment with crops that are heat-tolerant and drought-resistant. Diversification will need to be the leading component of adaptation.” South Asia is currently one of the most heavily irrigated areas on earth. Worldwide, about 70 percent of the water that we take out of the ground goes to agriculture. In the U.S., that proportion is slightly less because of efficiencies and precision irrigation techniques. In India, however, it is over 90 percent. As a result, India has by far the most stressed aquifers in the world. Eastern China is also stressed, as are parts of the southern Oglala aquifer in the U.S., which are overdrawn, but not to the same degree. The U.S. is wealthy enough to have irrigation practices that are more conservation-oriented and reliable. Virtually all global groundwater aquifers are being depleted. But there is no question that India is going to be experiencing this problem first.This is an aquifer in the western portion of the Indo-Gangetic basin, where India meets Pakistan. The major growing area there is the Punjab. It is a semi-arid region, a desert in places. Yet it is intensively irrigated. They grow rice in the summer and wheat in the winter.Some estimate in  Punjab, the aquifers will reach critical condition between 2025 and 2035. Others say by 2040. Some aquifers already have. So the situation is looking pretty dire there. That whole agricultural region, which is the most productive in South Asia, stands to fail. 

Part of this issue is that there is a very cheap baseline price for electricity for farmers. It is essentially subsidized. You can pump up as much water as you want and not feel any pain from overdrawing the resource, with the result that there is very little precision irrigation. There are really no incentives to save water. The minute you try to impose a tax, or raise the price for overdrawing the resource, you get a massive backlash. Once you have subsidized it for so long, the addiction is there, so what are you going to do?The Indian government is experimenting with artificial recharge — digging channels to redirect rainwater into the wells so that it can be funneled back into the aquifer. In other words, they are researching the possibility of using the same infrastructure that brings the water up from the water table to recharge it.

In central and south India, the government is also pushing community-based watershed management. For example, encouraging farmers to build farm ponds — low-tech community reservoirs that harvest rainwater for immediate use that season and also for natural recharge. Those systems work if they are married to [smallholder farming] and a more traditional view of what agriculture is meant to accomplish. More of the water in the east comes from Himalayan snowmelt and rainwater. Those glaciers have been melting quite rapidly, particularly over the last 10 or 15 years due to climate change. That can lead to flooding, made worse by really strong monsoon rains. With glacial melt, you get more water in the short term, but it’s a finite resource that is not getting replaced. So maybe you’ll have lots of water in the next 30 or 40 years, but by 2100 you’ll get deficits.

The consensus that is emerging right now— and this is true globally — is that, with climate change, we expect wet areas to get wetter and dry areas to get drier. And for those regions that are a combination of the two, like India’s monsoon areas, most of the models say that we will have more rainfall, but that a lot of it will come in more extreme events. So that if you tally it up over the four-month monsoon season, it looks like you’ve got more rainfall, and that might be a positive, but if it is all coming down in four or five massive events, then it is going to lead to flooding and soil erosion.

Even under normal monsoon conditions, you can go for two weeks without rainfall and then suddenly get a deluge, so that is very unpredictable. We think climate change will make this unpredictability worse. It may also tip the scales toward stronger droughts, perhaps, and longer droughts. When you talk about drought you are really talking about loss of water at depth in the soils. With water tables already in retreat in most of India, this becomes an especially severe problem. “Adding all that surface water from irrigation actually changes how the monsoon circulates.”

In all areas with a lot of irrigation, we found that irrigation tends to cool things off. Temperatures still rise due to climate change, but less steeply. We do not see the extent of warming in the northern Indian region that we would expect given the degree of climate change that is happening. We think that is because of how much irrigation water is being added to the surface. You might think that this cooling is good, but ultimately it isn’t, because when that water runs out, you are going to suddenly feel that temperature effect and you won’t be adapted to it at all.

We also found out that adding all that surface water changes how the monsoon circulates. It actually changes the amount of water that is being taken from the tropical Indian Ocean and dumped onto the continent. It is slowing down that circulation.

How will climate change alter agricultural productivity?

In the Indo-Gangetic basin, climate change is going to decrease productivity of rice and wheat throughout northern India. This is primarily a temperature response. Wheat is a temperate crop. We are getting toward the limit of how hot it can get and still be grown. With the current varieties that we have now, we don’t expect it to fare very well under climate change conditions.

Diversification will need to be the leading component of adaptation. You have to hedge your bets. So instead of just planting rice or maize or wheat, you are going to have to plant multiple crops in case you lose one. Farmers will also need to experiment with crops that are heat-tolerant and drought-resistant, like chickpeas, pulses [lentils or beans], and coarse grains, like millet and sorghum. We can call these “orphan crops” because they haven’t gotten the kind of research and investment that the big four — maize, wheat, rice, and soybeans — have received. So there is a lot of room to traditionally breed and improve these varieties to the point where the yields become more competitive with the big four.

The great thing about these crops is that they are protein-rich and nutrition-dense, and they tend to do well in the Indian climate. The limitation is that they do not command as high a price or generally equal the yields of rice and wheat. That is changing, however, now that interest in [healthier] whole grains and pulses is becoming more in style. So the prices are improving.

Here in the U.S., about 60 percent of our maize and much of our soy is being converted into other uses that are not directly feeding people, like animal feed and biofuels. But in India, the vast majority of what is being produced is actually feeding people. Indian agriculture has very high conversion rates to food compared to other countries. The real agricultural challenge going ahead is not just upping the tonnage of production, but growing nutritious foods and creating food security for people. This is an approach that India is already well suited for.

Some big cities are already subsiding – the ground beneath Shanghai, for instance, is being pressed down by the sheer weight of the buildings above – and rising sea levels resulting from global warming will make the effects worse.

The cities named in the report are sinking for a variety of reasons. Jakarta is thought to be subsiding by 25cm a year largely because of groundwater extraction, and Houston is sinking as the oil wells beneath it are depleted. Bangkok’s skyscrapers are weighing it down, while London is slowly sinking for geological reasons: Scotland is slowly rebounding after having been weighed down by glaciers during the last ice age, which is pushing southern England downwards like a see-saw.

Jakarta, a city that’s sinking as much as 8 inches a year in places—and as seas rise, no less. Models predict that by 2050, a third of the city could be submerged. It’s an urban existential crisis the likes of which the modern world has never seen.Jakarta’s people are pumping too much groundwater, and consequently the land is collapsing underneath them. If Jakarta can’t find a way to hydrate its people some other way, it’ll keep sinking, pulling that new seawall down with it. It’s a glimpse of a dark future for much of human civilization, which stubbornly clings to coasts around the world.

Think of Jakarta as sitting on top of giant water bottles, aka aquifers. Forty percent of its 10 million residents get their water from pumping, so they’ve been draining those bottles, which consequently collapse, leading to land subsidence. Indonesia plans to move its capital to the island of Borneo, as Jakarta - on the north coast of Java island - is slowly sinking and suffers regular flooding.This, by the way, is not unique to Jakarta: California’s Central Valley has sunk by as much as 30 feet for the same reason. But because other nations have dealt with the problem, Jakarta knows how to fix it.

Due to Global warming, melting of ice takes place in both poles & sea level is rising every year. The ocean/sea is ingressing towards main land in various parts of the world.It is said twelve coastal Indian cities are at risk of getting submerged by 2100 if global warming continues unabated.These cities are
Mumbai, Chennai, Kolkota,Kochi, Visakhapatnam, Kandla, Okha, Bhaunagar, Mormugao, Mangalore, Paradip, Khidirpur and Tuticorin which could be three feet underwater by the end of the century.Sea levels around Asia have been rising faster than the average global rate, the IPCC report indicates. Extreme changes in sea levels, previously once-a-century phenomenon, could happen every 6-9 years by 2050. Besides, glaciers in the Hindu Kush Himalayan region will keep shrinking and the snow cover will retreat to higher altitudes. The report – described as a “code red for humanity” – predicts temperatures will be 1.5 Celsius higher than 1850-1900 levels by 2040, unless drastic cuts are made to global emissions before 2030.

Many of Asia's biggest cities, including Mumbai, Shanghai, Bangkok, Ho Chi Minh City and Jakarta are coastal and low-lying, making them vulnerable to rising sea levels and extreme climate events such as more frequent and deadlier cyclones.

237 million people in six Asian countries are at risk due to coastal flooding by 2050, a new study published in Nature Communications on October 29, 2019, has said. The countries include China, India, Vietnam, Bangladesh, Indonesia and Thailand. 

The study also notes that 300 million people would be under threat from coastal floods every year. That is nearly 73 per cent or three times more people being prone to risks .

In India, six times more people are at risk from coastal flooding. 36 million people in coastal regions were estimated to be under floods.

Presently we see the aggressive, surging sea waves of 7 ft height in Puri beach eroding Swargadwara & playing havoc among locals. Odisha has a coastline of 480km & these tides are ingressing in Satabhaya,Pentha in Kendrapada district, Astaranga & in Chilka estuary in addition to Puri.The Geo-tube wall recommended by IIT, Madras has failed in Pentha.The sea erosion become terrible during June to September.

We have not yet studied the impact of rivers of Odisha that fall in the bay of Bengal. But the scientific study on river Ganga & Brahmaputra tells the following story.Estimates of the sediment load are highly variable, ranging from 402 to 710 × 10⁶ tonnes/year for the Brahmaputra River and from 403 to 660 × 10⁶ tonnes/year for the Ganges River. Both these rivers carry predominantly coarse silt to sand-size particles.In comparison to the global averages, the denudation rates in the Himalayan river system are four-fold higher.

Trapping of the sediments by multiple dams on river Ganga has impacted the territory of India. The plains from Haridwar to Haldia have been formed by the sediments brought by the Ganga from the Himalayas. This heavy influx of sediments has counteracted the cutting action of the sea. The sea has a natural hunger for sediments. It eats up the land to meet this hunger. Thus we find that most seashores are stony.

This hunger was earlier satisfied by the sediments brought by the Ganga. That led to creation of new land. This process of land formation has been reversed after making of the Bhimgoda barrage on the Ganga in 1850s and Tehri Dam and barrages at Bijnor ,Narora & Faraka after Independence. As a result the sediments are largely trapped and do not flow to the sea. The hunger of the sea is not satisfied and the sea has started cutting into the land of India to meet its needs. The Ganga Sagar Island has lost about three kilometers land in the last few decades.

Sundarbans may lose islands at a faster rate.Sediment trapping due to the construction of dams and reservoirs in the upper stretches of the Ganga has had several other impacts such as siltation, changing of the river course and high intensity floods. The deposition of sediments due to the construction of reservoirs behind the barrages results in a decreased flow of sediments at the mouth of the Ganga, leading to the erosion of coastal areas.

A scientific study reveals that the delta at Diamond Harbor in Kolkata is shrinking due to sea level rise at a very rapid rate (5 mm/year), significantly higher than the global average of 3.2 mm/year. The Sundarbans has lost 3.71 per cent of its mangrove cover and 9,990 hectares of its landmass to erosion between 2003 and 2014, according to a study.

Mapping of 7500 km Indian coast line tells that the coast is being eroded since 1968.The ministry of Environment & Forest estimates sea level to rise by 89-879mm between 1990 & 2100, resulting in saline ingress into coastal groundwater,endangered wet lands & inundated coastal communities. One in five people living in urban areas in developing countries are within 10 meters above sea level putting them at risk from flooding & cyclone induced storm surges that are likely to increase due to climate change.Populations are most vulnerable to flooding in Asia.Asia accounts for three quarters of the total world population living within 10 meters above sea level.In Bangladesh more than 40% of land area is within 10 meters above sea level.In this 2% land area of the world,10% of world population live which counts 21% population of developing countries.