Grounding Mosquitoes

Researchers in Oxford and California have found a way to stop mosquitos from growing wings – keeping them grounded and stopping the spread of diseases like Dengue fever.

Writing in the journal PNAS, Luke Alphey and colleagues highlight how controlling the principal vector, the Aedes aegypti mosquito, can help to reduce the increasing problem of Dengue and dengue haemorrhagic fever.  Current vector control methods are simply not effective enough, and we’re now facing an estimated 50-100million new infections annually.

One promising method is to control the mosquito population by releasing sterile males – thus reducing the population in the next generation.   This is known as the Sterile Insect Technique, or SIT, and although it showed some promising results back in the 1970s, it’s not being used in any large scale programmes.  Another technique is to introduce a lethal or incapacitating trait into the females of the population, and as it’s the females who bite and spread disease, this is particularly appealing.

This new study is based on modifying the Aedes aegypti Actin-4 (AeAct-4) gene in such a way as to render the female mosquitoes flightless.  This gene is active in the pupae stage of the female mosquito, predominantly in the Indirect Flight Muscles.  The researchers created a modified insect where this gene is only properly expressed in the presence of tetracycline, through a method called the Tet-Off system.  In the absence of tetracycline, these insects reached maturity, but were unable to fly.

Allowing the insects to reach maturity unharmed is an important aspect – it means that the larvae can still develop and compete with other larvae, and then only the adult female – the one that causes all the problems – is affected.  This also means that, rather than having to rear and release swarms of modified males, we can transport and release modified eggs.  As the eggs can be stored and stockpiled, this should mean that any control programme can start with a far bigger push than if we are relying on the maximum mosquito-rearing capacity of a lab.

The eggs will hatch, and the females will be, essentially, killed off immediately – they will be unable to feed, avoid predators or find a mate.  The males, however, should then mate with non-modified females, passing the flightless mutation on to the next generation and rapidly reducing the number of mosquitoes around to act as a vector for disease.

28th Feb 2010

Gigantic shellfish fiends discovered in Cretaceous seas

New fossil evidence suggests there were gigantic sharks lurking in Cretaceous seas, around 90 million years ago, but they weren’t terrifying monsters – these sluggish fish probably sat about on the seafloor, munching on shellfish.

This isn’t the first time paleontologists have uncovered fossilized parts of Ptychodus mortoni but new findings in Kansas, US reveal these mysterious sharks that went extinct at the same time as the dinosaurs were probably much bigger and slower-moving than previously thought.

Based on fossilized teeth, scales, and parts of the jaw, the team publishing in the journal Cretaceous Research and led by Kenshu Shimada of DePaul University in Chicago, Illinois, estimate these sharks could have been over 10m in length – longer than two Humvees parked end to end, and larger than the basking sharks that cruise our oceans today.

The smooth shape of their scales suggests these sharks were not built for speed: fast swimming sharks tend to have more pointed scales that help to improve swimming efficiency by reducing drag.

Their flat, plate-like teeth would have been perfect for crushing hard shellfish.

It’s thought these ancient sharks may have looked similar to modern-day nurse sharks that spend most of their time resting on the seafloor – proving that not all sharks need to keep swimming to breathe, a commonly misconception.

Even bigger ptychondontid shark teeth have been found, suggesting closely related species to Ptychodus mortoni could have been even more gigantic, and perhaps were the biggest ever shellfish eaters known on earth.

But just why these sharks were so enormous, at the same time as many other creatures in the sea including clams and other fish, remains an enticing mystery.

28th Feb 2010

Invasion of the Alien Star Clusters

One quarter of the star clusters in our galaxy may, in fact, be aliens, according to a paper in Monthly Notices of the Royal Astronomical Society.

The Halo around our galaxy contains a number of clusters of stars, called Globular Clusters or GCs, which orbit the centre of the galaxy.  They tend to be more dense, older and contain more stars than the galactic clusters which form the familiar disc.  Astronomers have known for a while that a percentage of these GCs are alien in origin, captured as the Milky Way accreted dwarf galaxies, but estimating what proportion of these GCs are aliens has proven difficult.

Now, Terry Bridges, an astronomer at Queen's University in Kingston, Canada and Duncan Forbes of Swinburne University of Technology in Australia have used data from the Hubble telescope, among other sources, and compiled the largest ever high quality database recording the age and chemical properties of star clusters, and used this to estimate the proportion of aliens in our galaxy.

But how do you spot alien star clusters?  There are a few give-aways.  Firstly, you can observe how the clusters move – clusters from a dwarf galaxy may retain some of it’s momentum after being swallowed by the milky way, and this can present a distinct pattern.  The second method is to use the metallicity of the cluster as a measure of its age.  Metallicity can simply be thought of as the proportion of elements present that are not hydrogen or helium.   Older clusters, or those with less activity, would be expected to have a lower metallicity – this means that the relationship between metallicity and age can be used as a indicator for the history of a particular globular cluster.

Bridges and Forbes discovered two distinct groups – one a fairly constant age of around 12.8 Billion years, and one with a far wider range of ages.  This younger strand is likely to consist of dwarf galaxies accreted by our galaxy in the last few billion years, and accounts for hundreds of millions of stars – even as much as 25% of the galaxy.

Astronomers had already confirmed that two dwarf galaxies - Sagittarius and Canis Major – have contributed globular clusters to the Milky Way, and these made up a significant proportion of the 93 clusters studied.  However, even once these were removed from the equation there is evidence that the remaining clusters originated from an additional 6 as yet unconfirmed dwarf galaxies.

So as always, space is enigmatic and fascinating, and there’s lots more to learn!

28th Feb 2010

Fish use UV to spot the difference

Healthy coral reefs come packed with colourful fish and a new study reveals that the some fish send out private messages using patterns of ultra violet light that us humans – and many other animals – can’t see.

It can be very important for fish to tell the difference between different species, especially for damselfish. These feisty tiddlers defend their farms of seaweed from intruders, the worst kind being other members of the same species because they strongly compete for food and mates.

Ulrike Siebeck from the University of Queensland in Australia led a team of researchers with the enviable task of studying two species of damselfish on the Great Barrier Reef. They discovered that Ambon damselfish, a small yellow fish, can read “secret” facial patterns of UV spots and stripes to tell one species from another.

The team presented wild Ambon damselfish with two other damselfish inside clear plastic tubes: one the same species, and the other a different species, the lemon damselfish that looks similar except for different UV facial patterns. Under normal light conditions, the Ambon damsels preferentially attacked other Ambons. But, when the tubes were made from UV-blocking plastic, the Ambons showed no preference for either fish, presumably because they could no longer see the UV patterns.

Also, in the laboratory, researchers trained the damselfish using food rewards to distinguish between drawings of the UV face patterns.

Together, these findings indicate that these Ambon damselfish can see intricate UV patterns and use them to recognize other fishes’ faces.

UV makes an ideal secret signal because not many other fish can see it. With its short wavelength, UV light is easily scattered in water making it of little use for precision vision. And long-lived predators often protect their eyes from UV damage by screening out these wavelengths. This means the damselfish can communicate to each other, find mates, and warn each other to keep their distance without ruining their camouflage against predators.

Next, the team wants to delve deeper into the UV vision of various fish, to find out at what distance they can see, and whether they can perhaps distinguish not only between different species but also individual fish.

28th Feb 2010

A Leak-Stopping System that really Holds Water

Helen -   This week, we’re looking at some of the scientific issues surrounding water, including how building a dam can change the local weather and how climate change looks set to affect water availability.  First though, the World Bank estimates that every year, 32 billion cubic metres of clean water is lost through leaky pipes.  Considering there are millions of people around the world without access to clean water at all, this seems incredibly wasteful.  But there might be a solution.  A Southampton-based company have come up with a leak-stopping system that really does “hold water”.  We sent Meera Senthilingam to find out how it works.

Meera -   This week, I’ve come along to the head office of I2O water in Southampton, a company whose main aim is to reduce water loss in urban environments, both here in the UK and globally.  They've set about solving this problem by developing a new technology that monitors the pressure in the flow of our water supply.  Here to tell me more a bit about this is the technical director here at I2O, Andrew Burrows.

Andrew -   Globally, water loss can vary between 15% and a massive 60% of the distribution of water inputs.  In the UK, it’s currently running at about 23% of the inputs lost as leakage.

Meera -   Why is water lost in this way and how difficult is it to control that?

Andrew -   Well, even with the latest technologies in water pipe works and network installations, the installation is always going to be a very complex network of pipes with many hundreds or thousands of connections between the individual pipes of the distribution network and also the connections for each individual property.  So it’s inevitable that there will be a level of leakage in the network.

Meera -   You've actually set about solving this problem by keeping an eye on, and controlling the water pressure through our pipes.

Andrew -   Yes, that’s right.  A significant influence over leakage and also over the frequency of bursts in the network is the pressure of water in the network.  Water pressure can affect burst frequency.  So the likelihood of a burst occurring, or a new leak occurring, is related to the pressure, as you would expect.  The rate of flow through an existing leak is also proportional to pressure.  The higher the pressure, the higher the leakage through existing leaks.

Meera -   So to set the scene a bit, how is our water distributed from the main source of water to a residential area?

Andrew -   Water is typically sourced from either reservoirs, holes, abstraction from rivers, or desalination plants.  That water is then filtered and treated with chlorine.  It’s pumped into a trunk mains system which is running at a very high pressure.  That trunk mains system comprises of very large diameter pipes that feed into the distribution network through metres and fixed outlet PRVs which are pressure reducing valves, set at a fixed outlet pressure.  That water is then distributed along pipes running down the roads with many hundreds and thousands of connections, supplying water to each individual property.

Meera -   We’ve got a mock up here in front of us which has a pressure reducing valve.  It’s about half a metre in length.  But above this, you've got small black device which is connected to the pressure reducing valve and is monitoring the pressure of the water  - both before and after this valve.  How does your system work to control the pressure of water that’s leaving this valve and reaching a distribution area?

Andrew -   The system comprises a controller, which is an electronic device, which interfaces with the pressure reducing valve which controls the pressures in the districts.  There’s also a remote sensor or remote sensors which again are electronic devices, monitoring pressures.  These devices communicate over the internet to a centralised server.  The server processes their data, learns the relationships between pressures and flows, and sends instructions back down to the controller.  The controller uses these instructions to continuously adjust the pressure reducing valve, to vary the pressure constantly during the day, to maintain the minimum possible optimum pressures in the network.

Meera -   Within this controller itself - you have one here opened apart - it’s pretty complex in there.  There’s a modem in there, there’s a battery.  It looks extremely complicated.

Andrew -   The devices are really mini computers.  The biggest challenge for us was energy because these devices are fitted in chambers in the ground, in the roads.  There’s no opportunity to fit a solar cell and we’ve got to run these devices for, typically, five years.  So , the devices have a key requirement for minimum power consumption.  They run from a single battery which is roughly twice the size of a D-cell battery, and that device is then monitoring the pressures through (RPST) or Resistive Pressure Sensing Technology.  The devices are recording the data and then connecting to the internet through the GPRS connection and transferring the data  only when they need to.  The control device also has to control the PRVs through a special valve.  The valve also requires minimum power consumption to make the changes.

Meera -   What have been the results so far?  Has there been a reduction in water loss?

Andrew -   In the UK, we’re working with all of the major water companies now and we’re seeing an average leak reduction of 20%.  On a typical district’s metering area, comprising say, 2,000 properties, we’re seeing reductions of around about 60 to 80 cubic metres per day.

Meera -   Now an important part of this though is that their benefits extend beyond simply controlling the water loss...

Andrew -   Yes.  Water distribution requires water to be pumped from the water source to the trunk mains.  The pumping in the UK uses approximately 1% of the total electricity produced in the UK.  So by reducing leakage or reducing the quantity of water to be pumped, there is a significant impact on carbon being produced by those pumping stations.  We would be reducing the amount of chlorination that required at the treatment works.  Also, there will be fewer bursts which will reduce the social impacts of repairing the bursts.  So as you can see, controlling the pressure has a wide range of environmental benefits.

Helen -   That was Andrew Burrows, technical director at I2O, explaining to Meera Senthilingam how careful control of the water pressure in our pipes can lead to a dramatic reduction in the amount of water needlessly lost and wasted in urban water supplies.

February 2010

Dam a River - Change the Weather

Ben -   Most of the water that we use comes from reservoirs.  These artificial lakes are often created by damming a river.  Once a large enough body of water has accumulated, you can tap it off, purify it and send it out to peoples’ homes; or you can release it back through turbines in the dam to generate hydroelectric power.  Simple as this sounds though, there are environmental consequences, including an effect on the local weather.  Dr Faisal Hossain is from Tennessee Technological University, and he joins us on the line now.  Hello, Faisal.

Faisal -   Hello, Ben.  Good afternoon.

Ben -   How many dams are there in the world?  Do we actually know?

Faisal -   Getting a precise number is tough but large dams, which are defined by the International Commission of Large Dams as more than 15 metres in height; they're probably about more than 100,000 of these around the world.  And approximately, small and large, we might have about a million dams.

Ben -   Right!  A million dams sounds like an enormous amount.  How long have they been around?

Faisal -   Most of them were built in the early 19th century, all the way up to, I think right after the Second World War.  Then in the ‘60s, I think the environmental issues of it caught up, and most of them were already built, so it stopped right on that time.  So, the typical age is probably a few decades. Maybe two to three decades or more.

Ben -   That seems fairly old for something that we rely on quite so much.  Were they built to last?

Faisal -   Well, dams are generally built to last.  You could say, they should last almost forever if they're properly maintained and operated. You should be able to use the dam for what it was built for, for as long as you want.  But there are issues with dams, like they get filled up with sedimentation and silt.   Sometimes, dredging of the dam and all that gets a little hard and it makes more sense not to use the dam or to decommission or remove the dam from the river.

Ben -   I’d imagine, removing a dam is quite an engineering task as well.

Faisal -   Yes, it is.  It’s still not a very well understood discipline.  It’s just coming up because now, we have to worry about what we’re going to do with some of these dams that we built.  We really didn’t think about what we were going to do when we built them, if they were not to last forever.

Ben -   We can see fairly obviously that dams change the river flow in any particular river that they’re put into, but what influence do they have on the local weather?

Faisal -   The first thing is, it’s a dam. It impounds the river and it creates an open body of water which is an artificial reservoir or a lake and that itself, being exposed to the sky and the sun, creates a huge source for moisture in the air.  That as a quantity may not be much, but if you factor in the other applications for which a dam is being built in particular like say, irrigation; in which you're drawing the water from the dam, the reservoir, and then you're irrigating thousands and thousands of square miles or kilometres, you're actually adding a tremendous amount of water vapour to the air.  Thereby, you can actually change a lot of the dynamics of how the rainfall used to form in the pre-dam era.  You can drastically change it to have more rainfall and much heavier rainfall than normal.

Ben -   So it’s not just the building of the dam itself, but it’s what you're then going to use the water for?

Faisal -   Yes.  If you just look into the dam itself, that won't be much.  You have to look into the changes in the landscape and the land use that it triggers, and most dams do because a dam will typically make a region downstream safer from floods.  So there’s more urbanisation which again has impact on the weather; then you can have more irrigation, or more recreational uses.  So you do change the landscape in a fairly drastic way, systematically.  It doesn’t happen overnight, but it happens on scales over a few decades, and that in turn will lead to some significant changes in the local climate, depending on what kind of climate zone it is in.

Ben -   This all seems very logical - that when you bung up a load of water and spread it out around the land that you're going to end up with changes in the weather.  But do we have any actual evidence that this is happening?

Faisal -   Actually, we do because there were a lot of studies done by some of my colleagues that we’re trying to work with now.  At the University of Colorado, Dr. Roger Pielke, who was an expert on climate, he and his colleagues have shown that actually, with irrigation and particularly if you have a very heterogeneous landscape, you can  increase the thunderstorm activity.  In other words, you can make the thunderstorms more frequent and you can make them much heavier.  So there’s short bursts of cloud water pouring in.  You can make them much more extreme.  So those studies have been there, but the connection to the dam and the reservoir as a triggering mechanism has really been looked into from an engineering perspective.

Ben -   And thinking of the engineering perspective, if building a dam does cause an increase in local rainfall, does this mean that actually, the dams themselves have been designed for less water flow than we now get?

Faisal -   That is a possibility.   Of course, the impact that a reservoir, with its land use change, creates is not uniform or consistent throughout the world.  Usually, you might see most of the impact in arid and semi arid regions as we are seeing in our research.  If they do change a lot of the rainfall patterns and you end up seeing more rainfall than the “normal” for which it was designed, yes.  That, together with the compounding problem of increasing sedimentation or loss of storage can make the situation a little worse.  In other words, you’ll have more water coming in from upstream, but then every year we’re losing a lot of storage in the dam.  So it means you actually have them to keep the gates open more than what was designed for.  So that is always a possibility.

Ben -   Does that, in turn, mitigate some of the beneficial effects that you get such as reducing flood risks, if actually, you're keeping the gates open a large proportion of the time anyway?  Do you still get the floods downstream that you would’ve got before the dam was built?

Faisal -   I think it still does mitigate the big floods.  I'm a civil engineer by training, and by the nature of my training, I am very much a pro-dam person.  But as engineers, when we built the dams, we always treated all these design parameters for which we build the dam as static . As in, it’s going to be the same a hundred years down the road or 500 years down the road.  We never considered that the very structure that we’re building and the applications that they're serving might itself compromise the design parameters.  So, yes - it may not be as successful or as effective as it was before for flood control, but it will still have some value.  I think the key thing is to understand for which regions and what type of dams and land use this will be an issue, and to modify our practice of operating the dams that’s much more climate friendly and much more sustainable in the 21st century.

Ben -   With a better knowledge of the impact of building a dam, are we now in a position where we can predict a bit better what would happen if we were to build a dam or if we were to decommission one?  What sort of predictions could we actually make?

Faisal -   Actually, we are - independently, a study of the impact of human activities on the local weather has been going on since a few decades ago.  So there’s a rich body of research that’s been done.  People have looked into how urbanisation affects local weather, how irrigation does, how other types of land use change impacts weather - especially the rainfall.  So I think we’re poised at a very interesting time where we can connect all this to the dam building practices, and we’ve got excellent computer models that can actually project either 50 or 100-year scenarios into the future of how the local weather might change.  And I think this is what the civil engineering profession has to embrace - to be able to do a much better lifecycle analysis, throughout the entire lifespan, predict the major extreme conditions and kind of plan for it in the design itself.

Ben -   Well I think that sounds like a very promising future for the future of dam design and dam building.  That was Dr. Faisal Hossain.  He’s a researcher at Tennessee Technological University, where he’s been looking at how dams alter the local weather.

February 2010

NEPAD Water Initiative

Ben -   For many of us, a glass of clean water is literally just a turn of the tap away.  But in many countries, millions of people still don't have access to safe water or sanitation.  The death toll directly linked to this is 1.6 million people per year.  This is not an insignificant fraction of people.  One initiative that’s been trying to tackle the problem South Africa is the South African-based New Partnership for African Development or NEPAD for short.  Meera Senthilingam spoke to Eugene Cloete, from the University of Stellenbosch who chairs the executive committee heading the initiative.

Eugene -   NEPAD is an acronym for the New Partnership for African Development which was formed to address a whole variety of issues on the African continent.  It was decided that water science and technology would be one of the flagship programs.  And the way that they organised this was to identify people working at research institutions and universities in the South African Development Community countries who we have competence in the field of water research.

Meera -   So what are the main aims of the NEPAD water initiative?

Eugene -   Well first of all, it is to build capacity in terms of people that could go into government and people that also, at the technical level, could champion certain initiatives that will increase the sanitation situation, the water quality in terms of potable water guarantees, to improve conservation and the utilisation of the continent’s water resources and then also to enlarge the range of technologies for water supply and approve access.

Meera -   But how big a problem is water availability exactly in the Southern African countries?

Eugene -   They have this saying in Africa that water comes in three forms: too much, too dirty, or too little.  All three of these are addressed by the NEPAD initiative.  We can take a few countries here and we can look at say, the urban and rural areas.  If we take for instance, a country like Mozambique which has a population of around 20 million people, 47% of the people there have access to safe water in the urban area, and in rural areas, only 40%.  So, it would be approximately 10 million people there that don't have access.  If we go on to sanitation in Mozambique, the situation gets worse, only 53% of the people living in urban areas have access to improved sanitation.  This would be something like a flush toilet, while in rural areas, only 15%.

Meera -   So that’s a high percentage of the population that don't have access to clean water and sanitation, but what are the actual causes of these?  What are the issues that need to be addressed in order to help provide access to this other 50%?

Eugene -   Well first of all, where people live.  The distribution of people, they live scattered very often over the countryside.  Where you have small villages where it would be very difficult in terms of economic considerations but also, very often, practical considerations to pipe water to these communities.  If they were living altogether, in an urban environment, it becomes a lot easier and this is why we have much bigger access to safe water in urban environments.  The other is purely the lack of knowledge on how to clean water, so that it becomes potable for human consumption.  It gets worse when you talk about sanitation, because if you rely on water-borne sanitation, you need a lot of water.  Now many, many people in Africa do not get their water coming out of the pipe, they do not have a flush toilet, they have to walk 4 to 5 kilometres a day to fetch water and they will not use that water except for cooking, washing, and drinking.

Meera -   What is the initiative actually hoping to do then in order to tackle some of these issues?

Eugene -   We are looking at our range of projects at the moment.  The one is looking seriously at roof-top rain water harvesting because what that does is, it brings the water to people in a de-centralised fashion.  So it’s a new way of thinking about it, and there are a whole variety of different sanitation systems now which work with minimal water which can then be used for irrigation and you could actually have a zero effluent system where people can grow their own vegetables, and so on.  That’s one of the alternatives.  I don't think going the way of providing pipes in all of the areas is feasible.  Many of the people are not there on a permanent basis.  They are basically living in shanty towns and you don't necessarily want to entrench that by providing infrastructure there, but rather develop areas to which they can move with infrastructure.  The second is to use technologies for disinfection purposes.  For instance, the soda system developed in Switzerland, where you take water, put that into a plastic bottle, and you leave that out in the sun for a few hours, two to three hours, and that will sterilize the water.  We have also got a project based on nanotechnology for instance where we have in the bottle type filter, containing activated carbon and nano bioscience which then will provide safe water, both from a chemical, and a microbiological point of view.  The application of that would’ve been for instance in Zimbabwe.  About a year ago, there were 80,000 cases of cholera.  All those cases could have been prevented if people knew about these low-key technologies which could make that water safe.

Ben -   So it seems that there is small things that we can do will make an enormously big difference.  That was Eugene Cloete from the University of Stellenbosch.  He was talking to Meera Senthilingam.

February 2010

WATCHing Water and Global Change

Helen -   Another priority is for us to understand how people actually use water, and how climate change and the way we use land will affect the availability of water in the future.  Dr Richard Harding is from the Centre for Ecology and Hydrology and one of the co-ordinators of the European network of researchers called WATCH, and that’s short for WATer and global CHange, and he’s with us now.  Hello, Richard.

Richard -   Hello.  Good evening.

Helen -   Thanks for joining us on the Naked Scientists.

Richard -   Hello.

Helen -   Now, as we’ve just heard from Eugene Cloete, having clean, fresh water is something that many of us take for granted.  But it’s certainly not the case that everywhere on the planet, they have access to healthy, safe water.  So, what are the main problems linked to the availability of water, and our uses of it?

Richard -   Well, there’s many problems linked to the uses of water and we’ve heard a lot about them just now.  But we have to realize that the majority of the water that’s used across the world is actually used for agriculture.  Something like 90% of the water that is extracted in these dams and from the aquifers, the underground aquifers, are used for irrigating crops.

Helen -   So nine out of ten litres of water we use is for food essentially?

Richard -   Yes, that’s right.  That’s obviously an essential purpose.  Particularly at the moment, we’re having to feed something like 6 billion people.  There are many, many people, particularly in developing countries who don't have enough to eat.  In the future, we’re going to have to feed perhaps 9 billion people by the midpart of this century.

Helen -   Se we're looking at needing a lot more water to be able to feed all those people.  So, if water for agriculture is such an important and huge part of the global water cycle, is that what you at WATCH are focusing on?

Richard -   Yes.  What we’re trying to do in WATCH is firstly to identify exactly how much water we have.  And quite surprisingly, it’s quite difficult to get a picture across all the world that we trust of what the rainfall is, what the evaporation is, and what the runoff in the rivers is.  Then beyond that, we have to look at what the consumption patterns are now for agriculture, for domestic water use, for industry, and what they might be in the future, and what the consequences of that might be.

Helen -   And those are all things I assume that you're looking at, trying to collect more of that data and bring it altogether?

Richard -   Yes.  What the WATCH program is and actually, what many of the researchers at the Centre for Ecology and Hydrology do, is we’re trying to bring together the experts on the climate, the experts on hydrology who know about what happens to the water when it falls on the ground, and then there’s another group of scientists, the water resource engineers, who understand how you store water, how the population uses water, and how it’s supplied to the where it’s needed.

Helen -   And we’ve talked already about agriculture and I presume that as we change the way we use land and do different things with it, this must have a significant impact on water availability as well.

Richard -   Yes.  There’s a lot of issues in that.  Certainly, different crops use water in a different way.  Some crops use more water than other crops and certainly as you change [land use] - for example, as is increasingly happening, natural vegetation is cut down, and crops are put in - that again changes how much water is used and referring back to the scientist from Colorado, that in itself has an impact on the local and actually the regional climate.  We have to take all these factors into account, if we’re to make a good assessment, a realistic assessment of how much water we’ll need in the future, and where we should be growing food.

Helen -   Increasingly, many of us are living in huge cities.  Presumably, as we heard already from South Africa, providing fresh water for all those people is a huge issue and presumably, simply by building on the land and changing the way water behaves, we’re also changing the availability of the water for us to use elsewhere and in the cities?

Richard -   Yes, we are.  In fact, the concrete of cities uses a lot less water than plants.  So, on one hand, by concreting over large areas of farmland, you're actually using less water but there’s a whole load of other issues.  For example the rainfall. particularly in areas where it had a very heavy rainfall, will runoff city areas and concrete areas very quickly, and actually, that water is sort of lost to the soils in the surrounding groundwater.  There are sort of pluses and minuses to the local water resources, and that’s obviously before we consider the quality of the water that is in the cities and underneath the cities.

Helen -   We’ve already touched on the idea that we’ve got to feed lots of people, we’ve got to provide them with water, and that’s already straining our current resources, and that’s only likely to get worse as the population increases.  And then we’ve got climate change as well, to make things even more tricky.  Is that something else presumably that you've got to take into account?

Richard -   Yes, I think so.  As you referred, there’s actually many places in the world where we’re already using water unsustainably.  There’s many places in the world for example where the groundwater levels are dropping quite alarmingly because water is being pumped out to grow crops.  In the future, climate change is going to have an impact on that.  We’re actually quite uncertain about what rainfall patterns are going to be in the future.  We’re quite certain the temperatures will increase, and that will have an effect on increasing the amount of evaporation into the atmosphere.  But it’s much, much more difficult to predict what will happen to rainfall patterns because they're much more dependent on the patterns of depressions and circulations in the atmosphere.  But there is general agreement from all the climate models that the dry areas are going to tend to get drier and the wet areas are going to get wetter.  Of course, that’s pretty bad news because dry areas like the Mediterranean, like the Midwest United States, like South Africa, and Australia are all predicted to get drier.  Now we’re quite uncertain, so we’re not absolutely certain about that, but it is looking that climate change will be an additional stress on what is already I think quite a serious situation.

Helen -   Well thanks, Richard and just to finish things off, is WATCH going to be providing solutions or are you basically handing your information onto someone else to come up with an idea of what we can do to increase the sustainability of water use?

Richard -   Yes.  I'm afraid we’re probably unlikely to provide many solutions.  I think the solutions were very well summed up by your previous contributor from South Africa who was essentially, in essence, saying that we have to use water much more efficiently, much more cleverly, and make best use of the resources we have.  What WATCH can do is give us our best estimate of what we have at the moment, and what we’re going to have in the future.   This will help us to make plans and identify critical points and hotspots where we need, perhaps to put additional resources in, maybe to build more dams, maybe to improve the distribution of water, or even maybe change the land use practices in some of those areas.

February 2010

Water Pressure

Do a classic experiment to show why dams have to be so high and submarines so strong.

What you need

What to Do

What may Happen

You should find that you have a series of streams of water coming out of the side of the bottle. The ones nearer the bottom are faster and stronger than the ones at the top.

What is going on?

This is all because water is a fluid, it is squishey, this means that if you squash it in one direction it will push out in all directions. This is why when you squish water in one direction it squirts out the sides. In fact the pressure (force per square metre) is pushes out with is the same as the pressure it is being compressed by.

Water is quite heavy so the water at the top of your bottle will compress the water below, so the deeper you go the higher the pressure. Every 10m you go under water the pressure increases by one atmosphere. This is why submarines and deep sea diving suits have to be so strong to avoid being crushed.

This means that if you make holes in the side, the water next to the deeper holes will be pushed out much harder, so it comes out quicker and travels further. 

This is also the reason that hydro-electric dams have to be deep. The higher the pressure the more energy a kg of water releases as it flows through the turbine, so if you have the same flow of river and double the height of your dam you will double the amount of energy you can extract.

Written by Dave Ansell