In the path of a hurricane

Hurricanes are one of the planet’s most destructive natural weather phenomenons. With Hurricane Matthew currently making it’s way through the Caribbean, it’s important that communities adhere to local emergency services and action plans.

Hurricane Genesis

Hurricanes are very large storm whose birth originates in the tropical oceans. They rotate about a central axis commonly called ‘the eye’. The oceans are a massive source of heat energy. Variations in sea surface temperature result in pressure differences in the atmosphere which cause storms to build up.

Tropical storms are characterised by their geographic origins. Image: NASA

To be classified as a hurricane a storm must reach wind speeds of at least 74 miles per hour. The rotation of the Earth gives these storm their characteristic spiral shape. Cyclonic storms in the northern hemisphere rotate anticlockwise while those in the southern hemisphere rotate clockwise.


The main hazards from hurricanes are strong winds (up to 150 miles per hour for the very large storms) and high volumes of rain. Hurricane winds can uproot trees and destroy houses. Large amounts of rainfall in a short period of time can cause floods and rising groundwater tables.

The water-clogged landscape remains unstable, with increased risk of landslides and surface failures, for many years after a particularly large event. For example, there were increased number of landslides in Taiwan for 6 years after Cyclone Bhola.

Extensive damage after the 2005 hurricane Katrina. Total damage > $100 billion USD. Image: Mark Wolfe

Historically significant hurricanes

The effect hurricanes have on people’s lives is illustrated by the word hurricane itself; after the Caribbean god of evil, Hurrican. They are a devastating force of nature.

  • Cyclone Bhola (1970) is historically the worst event for deaths with reported numbers as high as 500,000 people dead, mostly in Bangladesh.
  • Hurricane Katrina, which struck the east coast of the U.S. in 2005 is the most costliest hurricane with overall damage exceeding $100 billion.
  • The 1979 Cyclone Tip was the most intense hurricane ever recorded with wind speeds around 190 miles per hour. It was also the largest hurricane with a diameter around 2,170 kilometres.
  • Hurricane Sandy (U.S. east coast, 2010) was an abnormally large event due to the fusion of a tropical hurricane and a winter storm. With rising temperatures due to global warming these hybrid-storms are expected to become more frequent.

What can we do?

Cyclone Mahasen hit Sri Lanka, Bangladesh and Burma last season in May and resulted in far less deaths than expected thanks to swift action from the local governments. This shows that rapid response can save lives.

Proper preparation and sufficient warning can save thousands of lives every year.

Houses with appropriate shelters (as in the U.S.) need to be built in hurricane prone regions. Proper training should be given from early school level onwards on the appropriate actions to take before and after such events: e.g. having enough clean drinking water, tinned food, spare batteries for lights, mobile phone chargers, first aid kits etc.

Have a rapid response system in place from the national governmental level to manage pre-event evacuation (if needed) and post disaster recovery.

There is no clear agreement on what sort of effects climate change and global warming will have on hurricanes. However most scientists agree that the change will be for the worse whether it is in the form of increased number of hurricanes each year, increased size of the hurricanes or changes to the length of the hurricane season .  We need to invest more into understanding the science behind these storms and the effects global warming will have on their magnitude and frequency of occurrence.

More information
[1] National Hurricane Centre
[2] George M. Dunnavan & John W. Dierks (1980). An Analysis of Super Typhoon Tip (October 1979), Joint Typhoon Warning Center,1980

Eruptions at Piton de la Fournaise volcano

Spectacular drone footage of the recent eruptions at Piton de la Fournaise volcano on Reunion Island.

Earth’s Average Temperature since the last ice age

A fantastic figure created by the wonderful Randall Munroe of xkcd.


Food insecurity follows floods in Sri Lanka

By Amantha Perera

Food shortages brought on by extreme weather events have resulted in almost a quarter of Sri Lanka’s 21 million people becoming malnourished, says a World Food Programme (WFP) document.

“The increased frequency of natural disasters such as drought and flash floods further compounds food and nutrition insecurity,” says the document, the latest WFP country brief for Sri Lanka, released in June.

As per WFP’s most recent Cost of Diet Analysis, almost 6.8 million (33 per cent) Sri Lankans cannot afford the minimum cost of a nutritious diet and a large portion of this vulnerable population lives in poverty and is frequently subjected to extreme weather events.

Loss of land and livelihood from flooding caused to erratic monsoon rains. Image from Flickr.

In May heavy rains, brought on by Cyclone Roanu, affected 340,000 persons in 22 of the island’s 25 districts. “These people have very limited coping mechanisms, and these kinds of disasters can drive them deeper into poverty,” says minister for disaster management Anura Priyadarshana Yapa.

After the landslides and rains the government decided to shift out those living in high-risk areas but, according to public officials, they were faced with the problems of locating safe land and making income from agriculture.

“Most of those living on these high-risk areas rely on agriculture and we need to see how to secure their livelihoods,” head of the disaster management centre, Kegalle district, tells SciDev.Net.

The UN estimates that every year around 700,000 Sri Lankans are impacted by extreme weather, some repeatedly. “A sizeable segment of the flood affected population are squatters living in vulnerable areas prone to frequent flooding,” the UN Office for the Coordination of Humanitarian Affairs said following estimates made soon after the May floods and landslides.

“We need to develop long-term solutions, not stop-gap answers,” says Yapa, agreeing that there were serious problems arising from erratic weather patterns in Sri Lanka in recent years.

This article was originally published on SciDev.Net. Read the original article.


Earth’s Changing Surface water

Scientists have used satellite observations to study how the distribution of land and water on the Earth’s surface has changed over the last 30 years.

They found that the Earth’s surface has gained 115,000 sq km of water of extra water bodies and 173,000 sq km of water has now become land. The study is published in Nature Climate Change.

The interactive Aqua Monitor was developed by the Deltares Research Institute in the Netherlands. It is the first global-scale tool that shows, with a 30 metre resolution, where water has been transformed into land and vice-versa.

New lakes – seen in blue – are appearing on the Tibetan Plateau. Image: Deltares Aqua Monitor

The largest increase in water has been on the Tibetan Plateau, where increased water from melting glaciers are creating huge new lakes.

A rise in the number of dams built over the last 30 years has also increased the number of inland water bodies. Using the satellite data, the team were able to identify previously unreported constructions in Myanmar and North Korea.

The Aral Sea, which lies between Kazakhstan and Uzbekistan, has seen the the greatest conversion of water into land. Formerly one of the four largest lakes in the world, the Aral Sea has been steadily shrinking since the 1960s after the rivers that fed it were diverted by Soviet irrigation projects.

The Aral Sea has almost completely dried out. Green here shows the area of water that has converted to land. Image: Deltares Aqua Monitor

There have also been striking changes along our coastlines. The largest coastal water to land change is the construction of Palm Island and adjacent islands along the coast of Dubai. Many countries have shaped and extended their coastlines by land reclamation, including almost the entire coastline of eastern China from the Yellow Sea all the way down to Hong Kong.

Big data at everyone’s fingertips
Universally-available analytics for big satellite data may have major implications for monitoring capacity. At the very local scale, members of the general public can now make assessments without expert assistance if their houses are threatened by coastal erosion. At the regional scale, countries can monitor their water body changes and assess flooding impacts and strategy for disaster risk reduction.

Jaap Kwadijk, the Deltares scientific director: “This has never been done before. So it is difficult to imagine all the new applications that will be made using this tool. But the tool can be used by everybody and so I am sure multiple applications will emerge in the next few years”.

Original Paper:


Snow algae speeds up Arctic melting: Tiny creatures with a big impact

by Dr Stefanie Lutz

The enthusiastic skiers or snow hikers among you may have already experienced the red snow phenomenon, which is caused by tiny microorganisms – the snow algae. Often termed ‘watermelon snow’ because of its colour and scent, I would not recommend eating it though. All the algae need to thrive is sunlight and liquid water. That’s why they form massive blooms in the warm months in spring and summer. But too much sun is not good for them either. They produce their own ‘sunscreen’ in the form of red pigments (the so called carotenoids), that gives them their red colouration.

Greenland_Mittivakat glacier_Red snow_copyright LGB
Red snow algae sampled colelcted from the Mittivakat glacier in Greenland. Image copyright: Liane G. Benning

Red snow looks very pretty, but why should we care about these tiny organisms? Well, even the smallest organisms can have a large impact. The red coloration darkens snow and glacial surfaces. This decreases their so called albedo. The albedo determines how much sunlight is reflected back from a surface. White snow reflects more sunlight, whereas the darker red snow reflects less. Therefore more heat is retained, which causes more melting. It is the same effect that makes people choose white clothing in places with high sun exposure such as deserts. Black clothing would make the sun even more unbearable.

I was really lucky to work on this topic during my PhD at the University of Leeds. Together with my supervisor Liane G. Benning, we collected 40 samples from various places in the Arctic, ranging from Greenland to Iceland, Svalbard and Northern Sweden. We found that these algal communities are very similar in all studied places and over one melt season they reduce the albedo by an additional 13%. Calculating how much this equates in additional melting is not easy and will be addressed in our ongoing work.

A colony of red snow algae under the microscope. Image copyright: Stefanie Lutz

Our findings have been published in Nature Communications. Since the paper was published I have been approached by a many worried journalists who aske me what we should do against these dreadful algae. Well, we cannot and should not do anything against them. Snow algae are actually very important members of the natural food chain. Like plants, they do photosynthesis, and in doing so they fix atmospheric CO2 and transform it into organic carbon that can be used by other organisms. However, there is one thing that is worrying – and that is global warming, which may cause a ‘runaway effect’. Snow algae need liquid water to bloom, with rising temperatures more melting will increase the extent of the snow algae, which will further darken the glacial surfaces, causing more melting, and so on. So the only thing we can and should do is to reduce human-induced climate change.

We’ve just come back from gathering samples from the Greenland Ice Sheet, where a record-breaking ice melting enderway. As part of a big international, UK led team, we will further investigate the extent of these algae and their contribution to melting. At the moment climate models don’t consider the effect of algae on snow and ice melt, it is time to change that!

Dr Stefanie Lutz is a postdoctoral research associate at the GFZ Helholtz centre in Potsdam, Germany.

When continents collide

Since 1900, 35 earthquakes worldwide have each killed at least 10,000 people. Of these, 26 were in the Alpine-Himalayan seismic belt – a broad “crumple zone” where the African, Arabian and Indian tectonic plates collide with Europe and Asia. Most of these deadly earthquakes were caused by the rupture of faults that had not previously been identified.

Tim Wright is Professor of Satellite Geodesy at the University of Leeds and Director of the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET). His work has been at the forefront of developing the use of satellite radar for measuring tectonic and volcanic deformation.

Below is a lecture presented by Tim at the Geological Society talking about his work trying to understand the nature of seismic hazard within the Alpine-Himalayan region.

Quote: Marcia McNutt

“A natural hazard need not become a human disaster if society learns and applies lessons in preparation and resilience.”

Marcia McNutt, National Academy of Science, Engineering and Medicine.

Massive earthquake threat lurking beneath Bangladesh

A megathrust fault could be lurking underneath Bangladesh, India and Myanmar, exposing one of the most densely populated regions in the world to the risk of a large earthquake, according to new research published in Nature Geoscience.

A new GPS study measuring tiny ground movements since 2003 in the south Asia region has found strong evidence suggesting that a large tectonic fault beneath Bangladesh and east India is seismically active.

The new active fault beneath Bangladesh. Image from original paper, Steckler et al. 2016

The team, consisting of scientists from the USA, Singapore and Bangladesh, calculate that the megathrust fault could be accumulating strain energy at rates of about 15 mm per year.

Importantly, the researchers believe that the fault is “stuck” and has been storing energy for more than 400 years without a major earthquake; since the Mughal conquest of Bengal and the establishment of Dhaka as the Bangladeshi capital in the 1600s.

An earthquake occurs when the stresses become large enough that it causes the fault to break and releases all the stored energy. The 400 years of energy accumulation at 15 mm per year could result in a devastating magnitude 9 earthquake, similar in size to the Japanese quake that destroyed huge sections of the country’s northeastern coast in 2011.  Such an event would have enormous consequences for more than 140 million people living within 100km of the megathrust in Bangladesh and India.

Earthquake hazard and vulnerable populations in Bangladesh and India. Source: Steckler et al. 2016

The tectonic activity of south Asia is a consequence of the collision of the Indian subcontinent with Asia, a process that began nearly 50 million years ago and is still occurring today. This monumental collision resulted in the uplifting of Tibet and the formation of the Himalayan mountain range. Over millions of years these mountains have been slowly eroded and deposited their rich soils onto the Bangladeshi plains by a network of giant rivers. The thick sediments have made the Bangladeshi plains some of the most agriculturally productive in the world.

While the sediments can take up some of the energy along the newly proposed fault, they’re not especially stable, particularly around the rapidly developed eastern outskirts of Dhaka. If a major earthquake strikes, the sediments could even amplify the seismic waves, causing further destruction.

“Dhaka’s basically like building a city on a bowl of Jell-O [jelly],” says Steckler, lead author of the new study, implying that even small earthquake shaking could be amplified by the sediments.

The Savar building collapse in 2013, which resulted in over 1100 deaths, showed the world that building codes in Bangladesh are not strictly enforced. If buildings are collapsing on their own, it is a terrifying prospect to consider what would happen during an earthquake. The lack of preparedness is clear and it is essential for the Bangladeshi government to make long-term changes to promote greater seismic awareness and stricter enforcement of building codes.

More information:
[1] The original paper:

In response: Jet stream crosses equator

Recently a video has been circulating of Paul Beckwith from the University of Ottawa explaining how the northern and southern polar jet streams linked briefly across the equator this week.

Climate scientist Dr Caroline Holmes, who specialises in atmospheric dynamics, provides her independent view on this event below:

The essence of this video is the claim that the northern and southern hemisphere jet streams have connected via air crossing the equator, for a brief period of time; that this is ‘unprecedented’; and that it heralds dangerous consequences. To give my thoughts, I’ll address some of the concepts that come up in the video and some issues of language or terminology that are crucial for understanding it, and try to give an answer on whether I think this is a worrying development or not.

1) What’s so special about the equator?
Crash course covering two aspects: one is thermal, i.e., its to do with heat. As we know, the equator receives more heat from the sun than the poles do. Therefore it’s warmer. The atmosphere ‘tries’ to redistribute this heat from the equator to the poles, which is the reason for a lot of the circulation (i.e. large-scale movement of air and water) that we see in the ocean and atmosphere. Note, that in the northern hemisphere (I’ll call it NH from now on!) summer, the maximum heat from the sun is actually felt slightly north of the equator, and in southern hemisphere (…SH…) summer, slightly to the south of the equator. So, actually the ‘heat redistribution’ in the atmosphere is really from about 10°N to both poles in NH summer (SH winter) and from 10°S to both poles in SH summer. The other special thing about the equator is to do with the fact that the earth is a rotating sphere. So every point on the earth’s surface is rotating, once a day, around an axis that runs from the north to south pole. At the equator, this rotation requires covering a lot more distance (a circle of bigger circumference) than it does near the poles. So as air moves away from the equator (and indeed anywhere) it’s subject to forces linked to this rotation. (I’ll stop there because that’s a whole ‘nother blog post!)

2) What is a jet stream?
The term ‘jet stream’ typically refers to a tight (i.e. short north-south extent) band of very fast winds, high in the atmosphere. We usually use the wind speed at 250 hPa (i.e. the level in the atmosphere where pressure is 250 hPa; about 16 km, very roughly speaking) to describe it, although in some jet streams winds are fast near the Earth’s surface too. At the simple level, each hemisphere has one, or two, jet streams. One is on the edge of the tropics, and one is in mid-latitudes (broadly about 30-60°N). Sometimes, or indeed often, the two combine. The jet streams fundamentally exist because of the two things I already mentioned above; the rotation of the earth, and the fact that the atmosphere tries to distribute heat from equator to pole. In the time-average picture, they are nice and smooth, and largely west to east, although not entirely so, and in the NH especially they are not a continuous band around the world; they are split up by, in particular, the Rocky mountains and the Eurasia continent. As time varies, however, the jets have big waves in them; they break up; they shift from north to south; they pulse in strength. They are hugely variable.

3) Is the climate system normally ‘stable and predictable’ and now becoming ‘chaotic’?
The atmosphere certainly isn’t. One of the most fundamental things about the atmosphere is that it is a chaotic system. You’ve probably heard the ‘butterfly flapping its wings causes a hurricane around the world’ saying. It’s that. Or, less dramatically; tiny changes in the atmosphere in one place can push it into a different state from the one it was heading to. It’s why we can’t do weather forecasts perfectly; because without knowing the state (by which I mean its temperature, how much water it contains, how fast it is moving and in what direction) of every point in the atmosphere, perfectly, we can’t be sure we are on the right path. The climate system on the other hand is a much trickier issue. I’m not even sure what the video is trying to explain regarding this. There are aspects of the climate system that are certainly predictable (seasons, for example. And they aren’t going to be eroding in a hurry, because they rely on changes of the earth’s orbit around the sun and the angle of its axis, which happen slowly. I.e. 10s to 100s of thousands of years slowly.) The stability of the climate system is a genuine question. Imagine a ball on a slope.


If I shove it gently, it returns to where it was. This is a ‘stable’ condition. If I shove it hard, however, it might go over the ‘hill’ to the right; it will not return to where it was. This is what is meant by unstable. A related concept is ‘tipping points’; if it goes over that hill, it might end up in another ‘bowl’; but it has been tipped into another type of behaviour (in this case, a different area to roll around in).

4) What is climatology?
Climatology is a very broad field. It’s the study of climate. For example, it’s a term that could probably cover people who study the output from climate models about what will happen in the next century; look at observational data gathered over the past 100 years; examine tree rings to try and work out what has happened to climate over the last several millennia; use mathematical techniques to explore what will happen to earth’s climate, and so on. There are better, or more detailed description for all these jobs, but climatologist is not wrong. The key thing is that a professor of climatology need not be (and in fact, probably is not) an expert on atmospheric dynamics, i.e., the movements in the atmosphere and what causes them, which is what this is all about.

5) What is this graphic?

The jet streams. Image from:

It’s a beautiful visualisation of atmospheric conditions. It’s always worth being aware that first, the data that went into this is not as gorgeous as the end product! You can toggle the ‘grid’ button to show a point at every location where there is real data from the forecast model; the rest is interpolation between these points. And second, our eyes aren’t that good at interpreting information like this (sorry!) and are naturally drawn to colour boundaries. So, it’s easy to over-interpret patches of a different colour as indicating something very different. Now, as for some specific questions from the video, I’ll first address the idea that the jet stream should get, and is getting, ‘wavier’ as the atmosphere gets warmer. This argument is still, as far as I know, really controversial. I discussed this issue extensively during my PhD. The theory relies on a chain of about five causal relationships (i.e., A causes B, B causes C, and so on) in a chaotic system. Some of these are fairly convincing and some are not. The data providing evidence of this use information from a fairly short time series (30 years, which for finding robust results about anything other than time-average is too short). The original paper can be found here: However, later papers examining the claim across different datasets, and for various measures of ‘waviness’, don’t find strong evidence for such a pattern (e.g.…/10…/grl.50880/abstract). Therefore, citing it as fact is very misleading. The second question is whether something remarkable just happened, and whether it can be described as ‘the jet crossing the equator’. Flow crossing the equator is not surprising; as I’ve mentioned above, the atmospheric flow is very variable. A colleague at Monash University kindly quickly checked a month of reanalysis data (essentially, this blends observations- from the surface, satellites, and upper air measurements from weather balloons- with the best available weather forecast models, to produce a historical ‘best guess’ of what the atmosphere has looked like over recent decades). She found that the wind speeds with flow across the equator of the speed seen here (about 20 metres per second) aren’t that rare. So as above; flow across the equator isn’t astonishing. Can this be described as the jet crossing the equator? Tricky; not all fast upper level winds are jet streams, and in addition the jet streams are generally a lot faster than this (about 100 metres per second). So then, is this behaviour where there appears to be some linkage between the NH and SH jet surprising (even ‘unprecedented’)? Unfortunately I can’t answer that right now! Links like this are easy to see by eye, but harder to define when you look for it in real data, so it wouldn’t be a totally trivial job to find out. However, I think that there is no reason why it would be surprising; given that the jets move around, and airflow crosses the equator. For the same reason I don’t think it’s a particularly meaningful event. Finally, it’s worth saying, the jet streams have been exhibiting weird behaviour recently. The winter of 2013/14 was really remarkable in the NH, for example, and the UK met office produced a great report about the storms and floods that occurred in the UK as a result as well as what was happening in Canada at the time. So I think it’s important to understand what the jets are doing, and why, and whether it’s new. The changing temperature of our atmosphere due to climate change is hugely worrying, and how this might impact the jet streams, particularly in the northern hemisphere, is still poorly understood. However, in conclusion, I don’t think this particular instance is panic worthy.

Dr Caroline Holmes gained her PhD in climate science from the University of Reading, where her thesis investigated the effects of Arctic change (warming and sea ice loss) on mid-latitude climate, in particular the jet streams.  She now works on understanding the impacts of climate change in Scotland at the University of Edinburgh.

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