Connect with us

Planet Earth

River deltas are ‘drowning’, threatening hundreds of millions of people

The world’s river deltas take up less than 0.5% of the global land area, but they are home to hundreds of millions of people. Many live in major fast-growing cities such as Kolkata in the Ganges delta, Bangkok in the Chao Phraya delta, or Shanghai, one of dozens of large cities in the Yangtze delta region.

With fertile soils and easy access to the coast, deltas are critical hotspots of food production. Vietnam’s Mekong delta alone supplies almost 20% of the world’s rice. They also host unique ecosystems such as the Sundarbans in Bangladesh and India, the largest mangrove forest in the world.

But many of the world’s deltas are now facing an existential crisis. Sea levels are rising as a result of climate change, while deltas are themselves sinking, and together this means the relative sea level is rising extra fast.

Deltas are built from sediments that are carried downstream by rivers and eventually deposited where the river meets the sea. As these sediments compact under their own weight, deltas naturally sink. Where left undisturbed, the supply of new river sediment can compensate for the subsidence and help to maintain the delta surface above sea level.

But deltas are now subsiding much faster than they would do naturally. That’s thanks to groundwater being pumped (or “mined”) from aquifers underneath them and used to irrigate crops and provide water for rapidly growing cities.

In these circumstances, only the continued deposition of sediment on deltas can keep them from “drowning”. We therefore wanted to find out whether supplies of river sediments would be affected by future environmental changes.

To address this question, we used a computer model to project changes in the flows of sediment to almost 50 major deltas worldwide. We used the model to explore the impact of various environmental changes, including climate change, population growth, increases in wealth and the construction of dams. Our results are published in the journal Environmental Research Letters.

Rice farmers in the Mekong Delta, Vietnam.
Phuong D. Nguyen / shutterstock

We found that most of the world’s major deltas will receive less river sediment by the end of the century, regardless of the environmental change scenario. On average, we projected a 38% decrease. Our results suggest that many deltas – already significantly stressed – will become sediment starved, further compounding the risks of rising relative sea levels.

Some of the most severe reductions will be found in major Asian deltas such as the Ganges (81% less sediment) and the Mekong (77%). This is particularly concerning because these deltas are among the largest and most densely populated in the world.

We found that climate change will generally drive a small increase in the flows of sediments as, among other factors, warmer temperatures lead to increased precipitation and more soil is washed into rivers. But in many deltas this modest uptick will be more than offset by dams (which trap river sediments) and improved soil conservation practices as societies become wealthier. The Aswan Dam on the River Nile in Egypt or the Hoover Dam on the Colorado River in the US are among the dams that have already starved their downstream deltas of sediment.

Bad news for a river delta.
Tupungato / shutterstock

Better management of river sediment is vital to improve the outlook for the world’s deltas. International cooperation will be essential in deltas such as the Mekong and Ganges which are supplied by large rivers that drain many countries. For dams specifically, comprehensive environmental risk assessments that fully cost the consequences for downstream regions are required so that plans can be changed or scrapped. For those dams that are to be built in the coming decades, their design must accommodate transport of sediment downstream.

For authorities within deltas, faced with managing a dwindling supply of river sediment, new approaches are needed to better manage this precious declining resource. Flood embankments prevent sediment reaching delta plains and may need to be breached, as is being explored in the Ganges delta. Additionally, the removal of sand from rivers for construction materials, which is pervasive in many deltas around the world, must be better managed.

Ultimately, difficult decisions need to be made about development priorities between countries upstream of deltas and those including the deltas themselves, and there will be trade-offs to be made between hydropower, agricultural practices and delta sustainability.

Source link

Comments

Planet Earth

Powerful sprites over Kansas were visible to the naked eye

Have you ever seen sprites? They say that this is impossible. Strange and fleeting forms of Red Lightning materialize over thunderclouds, usually disappearing in less time than it takes to blink. However, storm hunter Michael Havan had no problems seeing them on May 23rd.

“The extremely bright jellyfish sprites were easily visible to the naked eye at dusk!” Says Gavin. “This is one of the brightest shots I’ve captured with my modified Canon T3i.”

Gavin saw this sight from Northwest Kansas. “Clear skies provided fantastic views of the MCS (mesoscale convective system) moving through Nebraska almost 100 miles from us,” he says. “I was not the only one who saw them.” There have been reports that people also saw sprites from Interstate 70. “

The storm lasted so long that Gavin managed to attach an 85mm lens to his camera for several close-up shots. “Because I had an image of the same area without a sprite from a few seconds earlier, I was able to subtract the sky (stars, air glow, etc.) to take a photo of the structure of the sprite without any distractions.

A solar minimum can stimulate sprites. During the low phase of the solar cycle — now occurring — cosmic rays from deep space penetrate the inner solar system relatively unhindered due to the weakening of the Sun’s magnetic field. 

Some models claim that cosmic rays help sprites get started by creating conductive paths in the atmosphere.

By the way:

Today, May 25, 2020, the level of cosmic rays crashing onto the Earth, reached its maximum levels, increasing today by 10.4% of average values.

Cosmic rays 

The magnetic field of the sun is weak, which allows additional cosmic rays to penetrate the solar system. Neutron counts from the Sodankylä Geophysical Observatory of the University of Oulu show that cosmic rays reaching Earth in 2020 are close to the peak of the space age.

Continue Reading

Planet Earth

A surge in volcanic activity threatens the Earth with a new Ice Age

Over the past few days, we have witnessed a turbulent global volcanic surge in activity. He sends us all signs that the Great Solar Minimum is approaching.

The Japanese meteorological satellite HIMAWARI-8 recorded two powerful eruptions on May 16, both of which occurred in Indonesia.

The first took place in IBU – a relatively new volcano with only 3 noticeable eruptions; in 1911, 1998 and 2008 – and was confirmed by Darwin Volcanic Ash Advisory Center (VAAC), which warned that the ash plume rises to about 13.7 km.

The second high-level eruption occurred just a few hours later on Semera – a very active volcano with an eruptive history; the first happened in 1818, the most recent in 2014.

As with IBU, the Semeru eruption was confirmed by both HIMAWARI-8 and VAAC Darwin, the latter confirming the generation of a “dark ash plume that reached a height of 14 km.

In addition, active lava flows remain active on the southeastern flank of Semeru, currently about 1.5 km long (as of the morning of May 18).

Direct cooling effect

These high-level eruptions are notable for the fact that solid particles are thrown to a height of over 10 km – and into the stratosphere – are often delayed, where they have a direct cooling effect on the planet.

Volcanic eruptions are one of the key factors pushing the Earth toward its next round of global cooling, with their worldwide surge associated with low solar activity, coronal holes, a diminishing magnetosphere and the influx of cosmic rays penetrating silica-rich magma.

In addition to Indonesia, Icelandic volcanoes have intensified, and it is this high-mountain volcanic region of the world that is believed to be home to the next “big eruption” – one that will plunge the whole world into the new Ice Age almost instantly.

Katla is such a volcano here and it shows signs of activity, since a significant gas output has been recorded over the past few days. 

In addition, seismic activity under a large ice volcano has also increased, and this activity is probably caused by injections of new magma entering the chamber.

Icelandic authorities are aware of the danger posed by the next Katla eruption, and a delegation of volcanologists regularly meets with the Icelandic parliament to discuss how to respond in the event of an eruption, the likelihood of which is simply a matter of when, not if.

Continue Reading

Planet Earth

99 years ago, the Great Geomagnetic Storm of 1921

99 years ago this week in May, people all over the world woke up and were shocked by some unusual headlines. “The telegraph service has been defeated, the Comet is not to blame,” the Los Angeles Times said on May 15, 1921. “Electrical disturbances are the worst ever known, “the Chicago Daily Tribune said. 

At that time they did not know this, but newspapers covered the biggest solar storm of the 20th century. Since then, nothing like this has happened.

It all started on May 12, 1921, when the giant sunspot AR1842, crossing the sun during the sunset phase of the solar cycle 15, began to flash. One explosion after another threw coronal mass ejections (CMS) directly to the Earth. 

Over the next 3 days, a powerful geomagnetic storm shook Earth’s magnetic field. Scientists around the world were surprised when their magnetometers suddenly got out of hand, pens in strip card recorders were uselessly attached to the top of the paper.

Auroras in May 1921. The leftmost red circle indicates Apia, Samoa.

And then the fire started. Around 02:00 Moscow time on May 15, the telegraph exchange in Sweden caught fire. About an hour later, the same thing happened across the Atlantic in the village of Brewster, New York. Flames swept the switchboard at the Brewster station of the New England Central Railroad and quickly spread to destroy the entire building. This fire, as well as another one at about the same time at the railway control tower near New York Central Station, is the reason this event is sometimes called the “New York Railroad Super-Storm.”

What caused the fire? Electric currents caused by geomagnetic activity passed through telephone and telegraph lines, heating them to a burning point. Strong currents disrupted telegraph systems in Australia, Brazil, Denmark, France, Japan, New Zealand, Norway, Sweden, the UK and the USA. The Ottawa Journal reported that many long distance telephone lines in New Brunswick were burned due to a storm. On some telegraph lines in the USA, the voltage reached 1000 V.

Sunspot AR1842 dated May 13, 1921

During the peak of the storm on May 15, southern cities such as Los Angeles and Atlanta felt like Fairbanks, with northern lights dancing overhead, while telegraph lines crackled with geomagnetic currents. Auroras were spotted in the USA right up to Texas, while in the Pacific Ocean red auroras were spotted from Samoa and Tonga and ships at sea crossing the equator.

What would happen if such a storm happened today?

Scientists have long discussed this issue. As a result of research, it was found that the storm peaked on May 15: its intensity was comparable to the intensity of the Carrington event of 1859.

This result disproves the generally accepted point of view. Space weather researchers believed the Carrington Event was the strongest solar storm in recorded history. Now we know that the May Storm of 1921 was about as strong.

If the May Storm of 1921 hit today, it would at least lead to a power outage, profound changes in satellite orbits, and the loss of radio technology such as GPS. GPS malfunction can significantly affect the operation of logistics and emergency services.

This is something to think about on the 99th anniversary of a 100-year storm ….

Continue Reading
Advertisement

DO NOT MISS

Trending