Examination of Witnesses (Questions 580
- 599)
WEDNESDAY 12 DECEMBER 2007
DR ANN
CALVER, MR
TERRY MARSH,
PROFESSOR JOHN
MITCHELL, MR
STEVE NOYES,
DR CHRIS
WEST AND
MS JACQUI
YEATES
Q580 Paddy Tipping:
Coming to your work, Dr Calver and Mr Marsh, in your evidence
you suggest that fluvial flooding is going to get less because
there is going to be less snow around and the soil is going to
be drier. We have had a prolonged discussion today about urban
flash flooding. As policy makers, do you think we ought to be
investing in the urban environment and taking measures in the
urban environment rather than flood defences?
Mr Marsh: There is an issue there
on the point we made in our notes to the committee. In terms of
fluvial flood risk, we did not say that it would reduce. We said
that there were factors that would moderate flood risk in the
future. In terms of fluvial flooding, there are two elements and
a separate feature which I will come to. The 1947 flood, the largest
of the last century, was primarily the result of snow melt. There
was some rainfall but it was a major snow melt event. The largest
event in the 19th century was probably the 1809 flood, and that
was in fact rainfall running off frozen ground, with some snow.
These are frozen ground and snow melt events. In a warming world,
climate change is seen as the villain of the piece too often,
but, in a warming world, that type of exacerbating factor will
be less important. The other issue is in relation to the dry warm
summers that we are likely to get. Under those circumstances,
the soils will be drier for a longer period. One would envisage
the reason that we have so few summer floods is that dry summer
soils are able to absorb a substantial proportion of the rainfall.
In the future, it may well be that the flood season, if you will,
is contracted. Those two elements could come together to reduce
flood risk. There is one final point in relation to fluvial flooding,
because there is a good deal of public fear out there that flooding
is going to increase very rapidly. The Thames is an interesting
example. It has one of the longest records in the country for
flooding. There is no trend in the flood magnitude on the Thames,
and that is over a period of 130 years. You could go further and
say that flood risk has actually declined, not vulnerability to
flooding because of development on the flood plain—there
is no change in flood magnitude through time—but the capacity
of the channel of the Thames has increased. The Thames is a more
efficient river, less romantic but more efficient, than it was
100 years ago. The weirs have improved. There are flood relief
schemes. Dredging has created a more efficient channel. An amount
of flow, an amount of water, that would have produced a flood
in the 1930s and 1940s is now readily accommodated in the lower
Thames. These issues are important. Some relate to potential climate
change and some relate to river management. If you also look at
the Warwickshire Avon where there was a staggering magnitude of
flows, there is no compelling long-term trend in flood magnitude
there either. Things may change but you have this relative stability
through a period when temperatures have increased, not as much
as they are likely to increase in the future, and the rainfall
patterns have changed from a situation where in the 19th century
summers were quite often wetter than winters and now we have wetter
winters. You do have this stability through periods of climatic
variability. I am not saying that these are grounds for being
sanguine at all. It may change but you can see that it is relevant
to the discussion, particularly in relation to the public's perception
of how bad things could be and how quickly. I am not sure I am
best placed to answer the question about—
Q581 Paddy Tipping:
Stick with that for a minute. There are reasons to be cheerful?
Mr Marsh: There are reasons to
be cheerful in the sense that there is some resilience to flood
risk, which perhaps is not discussed. If we get wetter winters
and more intense storms, then that resilience will be tested but
there is a degree of resilience.
Dr Calver: There is just a quick
point on whether we should invest in urban areas. In Environment
Agency and Defra parlance, risk is probability times consequences,
and consequences are usually likely to be more compelling in urban
areas. The point I would really like to make is that urban drainage
systems were designed perhaps more for drainage than for conveying
floods, and they are to a very low standard in terms of recurrence
interval events. I think new developments are somewhere around
the 30 years but many, many are a lot less than that. What we
badly need, if we are going to invest in that type of approach,
is knowledge of urban drainage behaviour above the current rather
low design levels. When we know how they behave, we can then see
if it is worth investment there. What developers must do is not
only solve their development patch but not pass the problem on
within an urban area and not pass it on within a catchment either.
Mr Noyes: This is a really important
point. One way that I tend to think about it is that a lot of
effort and investment has gone into understanding the meteorology
that gives rise to rainfall and the effect that then has on river
catchments and then what you do about managing the effect of rivers
in flood through managing the flow of the water but also on the
flood defences. I think historically that has been what one might
call a tractable problem in the sense that the science and the
engineering is established well enough to be able to do something
about it, to understand what is going to happen in the atmosphere
and what happens in the river catchment, and then how you deal
with it, how you design the management and mitigation systems
to deal with that. It is really only relatively recently that
the problem that you described in terms of urban flooding, flash
flooding, is beginning to become tractable because on an atmospheric
scale we are now beginning to model the atmosphere at a resolution
which is approaching the sort of resolution you would need to
be able to do something useful. Ordnance Survey and the like are
now gathering data around what is actually happening on the ground
at that resolution and also importantly keeping it up to date.
The water authorities and the Environment Agency are together
beginning to keep more records of what they are doing. Probably
for the first time it is becoming a tractable problem so that
we can actually start to provide some useful advice around it.
The area where it probably is possible in the longer term, and
we have already talked about this but it needs significantly more
work, is what is going to happen under climate change. On the
one hand, in real terms, in terms of providing forecasts so that
emergency services can respond to something that is going to happen
next week in an urban area, I think we are close, with more investment,
to people working better together and being more focused on that
issue to start dealing with that in terms of the here and now.
With more investment in understanding climate change and the links
to the hydrological impacts, then the engineering design solutions
should be available for the future.
Q582 Paddy Tipping:
This is the work that you were talking to us about earlier, Jacqui?
Ms Yeates: I understand the problem
is that as much as they can model the future climate change, ideally
I believe they would like 30 second information in terms of future
climate change. As the climate modelling people will tell you,
you just cannot have that. So there is still a mismatch between
the type of information required, because obviously rainfall intensity
is very important and that is why they ideally would like 30 second
rainfall. They cannot have it and I believe they ended up using
two minute rainfall with very large cautions around it given to
them via a weather generator. There is still a problem with the
level of information needed for this type of work and what can
actually be provided with any type of accuracy or certainty in
it. It is still very uncertain information we are dealing with.
Q583 Paddy Tipping:
This would be interesting data for insurance companies?
Ms Yeates: Yes.
Professor Mitchell: Just to comment
on the extreme events, in winter with both the mean rainfall and
the extreme events, the tendency increases in virtually all models
over the UK. As was indicated, in summer the mean rainfall is
split between getting wetter and drier, certainly in England in
the southern part of the UK. When one looks at the extreme rainfall,
there is still a tendency, even in some cases where a model is
producing a drier mean rainfall, for it to produce heavier extreme
rainfalls and so the heaviest day rainfall increases—not
in all cases but in many more than in the case of mean rainfall.
As Steve explained, that is simply because you have a moister
atmosphere and typically that is about 6-7% per degree. So you
have a rule of thumb for that particular mechanism. There may
be other things happening which might intensify the storm but,
in terms of the temperature effect, there is a very rough rule
of thumb of about 6-7% per degree in the maximum amount of water
that the atmosphere can hold at a particular temperature.
Q584 Paddy Tipping:
Sticking with the reasons to be cheerful, you seem to be telling
us that climate change can be more intense with heavy rain in
summer but longer, more protracted rain in the winter.
Professor Mitchell: Certainly
it can be wetter with an increase in mean rainfall and an intensity
in rainfall. In summary, the jury is split on what is happening
in terms of mean rainfall but there is a tendency in some of the
cases where models are producing a reduction in rainfall still
to have an increase in the extreme rainfall.
Q585 Paddy Tipping:
On the climate change pattern, what about tidal surges? East Anglia
was going to be overwhelmed at the beginning of November and narrowly
escaped that. What is the pattern of weather change on some of
those events like that?
Professor Mitchell: In terms of
storm surges, there are at least three main factors. One is what
is happening to the land surface in the south-east of England
as it is sinking. If you go to Scandinavia, it is rising. The
second is the change in mean sea level. The third is any change
in meteorology which increases the tidal events. If you look at
the last UKCIP report, I think there is a case of a high emission
scenario in somewhere like Immingham. A one in 100 year event
became a one in seven year event. The majority of that was due
to changes in the meteorology in terms of storm surges with slightly
less than half the contribution coming from sinking land and changes
in mean sea level. The more recent predictions that we have show
a smaller contribution from storm surges and a similar contribution
from mean sea level and so on. The predictions of storm surges
are even less certain than rainfall. I think one should be aware
of that, but that gives you a typical idea of changes in surges
down the southern North Sea.
Ms Yeates: That was the median
high scenario and not the high emission scenario. If memory serves
me correctly, it is medium high and not high.
Q586 Chairman:
Are all coastal areas potentially around the United Kingdom subject
to storm surge? Could any one occur at any time?
Mr Noyes: Yes, but to varying
degrees. I think that is the point. Storm surges are common but
when they become particularly severe is less common and it is
largely the area around the North Sea coastline that is most at
risk because of the collection of water in the sea pushing up.
One way of thinking about it is that if you push a tablecloth
on the table, it ruffles up. It is the same effect in that the
wind pushes the sea; it gathers at the bottom of the southern
end of the North Sea. You get storm surges all round the coast,
during the winter months in particular, but what is particularly
of concern is the shape of the North Sea basin and the gathering
of water in the North Sea.
Q587 Dan Rogerson:
On urban flooding, and we are talking about modelling, just in
terms of the weather that is on the way and the interaction you
see when you are looking at the fluvial events, you have that
relationship with the Environment Agency, which is very clear.,
When you are dealing with local authorities, I imagine that is
quite a different relationship to have one organisation with lots
of others. How does that interaction occur?
Mr Noyes: We deal with a lot of
different agencies. For example, if there is going to be an exceptional
weather event this coming weekend, we would already be talking,
as you say, to the Environment Agency. We talk to the local authorities,
both directly in terms of the ones that are most likely to be
affected, and also, through the Civil Contingencies Secretariat,
to the Cabinet Office. We also have contacts with the Fire Service
and Police directly. At different stages of the event, then we
would be talking to different people. If, for example a Gold,
Silver or Bronze Command was established, we would be in regular
contact with them. Indeed, we have a small team of people who
are located around the country called our Public Weather Service
Advisers whose sole role is to communicate with that community.
To the extent that they would be talking to them at any time of
day or night, they may indeed deploy to work alongside colleagues
in a Gold Command, should they wish it. We talk also to the Cabinet
Office and to government departments directly and to the community
of utilities of course which have an important role to play, whether
it be the water utilities, energy utilities, Highways Agency or
Network Rail and so forth. Those dialogues are happening all the
time. We tailor our messages to the people to whom we are talking.
As you say, the Environment Agency would probably want to have
a dialogue with us in one particular context, whereas Network
Rail as one example would be talking about the issue in a different
context.
Q588 Dan Rogerson:
Is that on the basis that they are asking you questions and you
are providing the answer or is that on the basis that you think
there is a matter of concern and you are initiating the process?
Mr Noyes: We initiate that. There
is a protocol whereby we contact them. There is a routine service
that happens in terms of alerting people during the routine service
that operates 24 hours a day, seven days a week. In addition to
that, over recent years we have developed matters and we have
found at the operational level that sometimes when we are talking
to our customers the high impact exceptional events do not become
escalated up. To get round that, at senior level we will make
direct contact with senior management in those customer organisations
so that senior management is aware that something is going to
happen and then they can gear up their own organisations.
Q589 Dan Rogerson:
But is it because of the way flood defences have been focused
on the river catchments? Is going into the Gold Command process
and all the rest of it really triggered by river catchment stuff
and the urban stuff is tacked on to it or if you are likely to
have an event that is happening in an area that is not part of
the significant catchment? Do you see what I am trying to say?
How would that go direct to a local authority rather than through
a wider process because of a concern over river catchment?
Mr Noyes: There is a routine protocol
for the warnings that we issue, and indeed the warnings that the
Environment Agency issues. We have something called the National
Severe Weather Warning Service, which would go to all the local
authority responders, but we do not deal with flooding; we deal
with heavy rain. The Environment Agency then deals with warnings
related to rivers. There is a gap, which is indicated in our submission
in terms of where you are driving to and that is the pluvial or
flash flooding, in UK capability in terms of warning people about
that risk.
Dan Rogerson: As the MP for Gloucester
and as you have mentioned a couple of times, the much smaller
event we had this year was far more connected with the surface
water coming there. I guess because the community had been through
it so recently, they were far more pragmatic about it and were
able to analyse for themselves what had happened and so it was
very different.
Q590 Mr Williams:
On the tidal surge issue, I can understand how seasonal and tidal
events are exacerbated and how wind can exacerbate that, but what
I did not understand was how in very low pressure conditions the
actual level of the sea rises. Is that right?
Professor Mitchell: That is true.
Q591 Mr Williams:
What causes that? Is the water becoming less dense or is it moving?
Mr Noyes: Think about the weight
of the atmosphere pushing down on the oceans. Pressure is just
a way of measuring the weight of the atmosphere above you. As
the pressure reduces, then the sea can rise higher, and so, yes,
it is effectively expanding.
Q592 Mr Williams:
So it is becoming less dense?
Mr Noyes: Yes. It is rising up
higher.
Dr West: It is rising up higher.
It is being pushed down more strongly elsewhere.
Dr Calver: If I may add a point
on that surge, the low pressure systems that cause this effect
can of course also be associated with inland flooding. Occasionally
you have what we call a joint probability situation with both
inland and coastal flooding and that of course can be one of the
occasions when you get very extensive flooding. It is worth thinking
about spatial extensive flooding in general because that is when
the emergency services are really tested. It is very bad if it
happens in an individual place but if you get a spatially extensive
event that is perhaps even worse. It is probably worth looking
into some of the circumstances that promote those events.
Q593 Mr Williams:
Could you explain how that works?
Dr Calver: Yes. The low pressure
that Steve and John have explained and how that causes a surge
is often also associated with a depression of a weather system.
If that tracks over the country in a certain way, it can sometimes
produce enough rainfall in locations so that there is big river
flooding, coastal flooding.
Q594 Mr Williams:
That is not to do with the lifting of the water?
Dr Calver: No, it is the precipitation
associated with low pressure systems.
Mr Noyes: There is a direct impact
on rivers from the surge. If you go back to the East Anglia event
we have talked about, and you can imagine the water egressing
the land through the river, if you have a storm surge, it is like
the tide staying in all day and so the water cannot leave the
rivers. If you take the East Anglia event, the flood defences
on the coastline held up, thank goodness, with just one breach
but the flooding we did have, particularly in Norwich, was because
the river flowing through Norwich could not get into the sea.
There are circumstances which are fairly common where a surge
will stop the river getting rid of its water.
Q595 Lynne Jones:
You commented a few moments ago that pluvial flooding, which is
a new word to me, nobody is responsible for forecasting. Also,
the Met Office in its evidence referred to the different system
they have from most of Europe where there is one single agency
responsible for all these forecasts. Are you implying that there
should be changes and, if so, what and who should be responsible
for pluvial forecasting|?
Mr Noyes: There are two parts
to the question and two answers. One is around pluvial forecasting
and what shall we do about that, and then there is a second point
which is: is there benefit to be gained from integrating more
closely how we model hydrology and how we model the atmosphere.
With regard to pluvial forecasting, because of capabilities that
are coming, and we could potentially accelerate those capabilities,
and, as I mentioned earlier, because of better understanding of
what is going on on the ground in terms of Ordnance Survey, better
records being kept of what is being put in the ground by builders
and developers and water authorities and better modelling of the
atmosphere by us, we can start really for the first time to be
doing pluvial forecasting and warning in a sensible context. I
think in Europe there is no difference. Everyone has the same
problem. Everyone is trying to come up with a way of forecasting
and warning early enough of flash floods so that people can do
something about it. In the Boscastle sense, people could be contacted
a few hours in advance and be told to evacuate to high ground
so that they did not have to be lifted by helicopter, for example.
That problem is the same in the UK as it would be in other parts
of the world. Everybody is now getting to the stage where we think
we can do something about that. The other is with regard to whether
there is benefit to be gained from more closely coupling the responsibilities
for hydrology and weather. We think that there is, and that is
evidenced by what happens in Sweden and in France in particular
within Europe. Why do we think there is benefit to be gained?
For a start, if you take the example within the Met Office of
the Hadley Centre, which looks at climate change and the weather
forecasting business, which is our traditional, core business,
by having them in the same organisation we have been able to develop
our science and our modelling in such a way that we end up with
a better understanding of climate change and the weather impacts
that then helps our colleagues in UKCIP to produce better predictions
of what the impacts will be. In the same sense, if you can couple
modelling of the water that then has fallen on the ground with
the way that you model the atmosphere and if the research and
development that goes into those are done with the same aim in
mind, then when we are developing our science for the atmosphere,
we can be very much gearing that to what is going to be done in
parallel with modelling the hydrology. At the moment, I think
it is fair to say that there is not so much co-operation and coupling
as there should be. There is a lot to be gained from putting much
more effort into a unified approach to how we do that in the future.
Q596 Lynne Jones:
In practical terms, what are you saying? It has been proposed
that the Environment Agency should take over this role. Are you
disagreeing with that or are you saying that you just need a much
better relationship or that you can provide better information
to the Environment Agency? You also said a few moments ago that
we could accelerate these capabilities. I assume things are going
ahead with your new super computer which will enable you to increase
the resolution of your predictions. What about other areas of
research into hydrology? Have we got the resources in there that
will maximise our capability in this area?
Mr Noyes: Again, there are two
parts to that in terms of the response. One is around who is best
placed to provide that once we have the capability in place to
do pluvial forecasting well. I will pass to John and colleagues
to my right in terms of how we might do that and where the research
should be focused. Bearing in mind that pluvial flooding is related
to high intensity events and the response is quite quick, river
flooding tends to be slower; there is more of a lag until the
response. Pluvial flooding is very quick and therefore we need
to get messages to the citizens very quickly, in the middle of
the night potentially. You need an organisation that is used to
providing that immediate advice to the emergency services. The
Met Office's view is that we are best placed to provide that advice
in an operational context because that is what we do now and we
already have the contacts. We are there all day and all night
every day of the year; the Environment Agency is not. That would
be our view in terms of the actual advice to the emergency services
and the public. With regard to the operational running of the
models, it would make sense for those to be done together so that
they are closely coupled. Where the research and development should
be done is less clear. I will pass on to John for that.
Professor Mitchell: To add to
what Steve has said, in particular on the operational modelling,
the running of the operational model I think would have to be
done in the Met Office because in coupling an atmospheric model
to a flow model, particularly if you go to high resolution perhaps
in samples, there is a lot of data streaming out of the computer
that has to be fed directly into the flow models. I think that
is where we would want to see it. In terms of giving the warnings,
I think that is just a matter of collaboration between the particular
environment agencies and ourselves. In terms of the research,
we do not have much expertise in-house in terms of flow modelling.
We have looked to people like the EA and to CEH and in fact on
the climate side we already have people working in Wallingford.
Dr Calver: We do have a small
Joint Centre for Hydro-Meteorological Research in the non-operational
sense that links the Met Office with our hydrological researchers,
which is quite a good model.
Professor Mitchell: That research
feeds both into the operational forecast and the climate forecast.
There is the basis of that collaboration already. The third thing
off the top of my head that is important is to second people particularly
from the Met Office to the Environment Agency and vice versa to
increase the knowledge and understanding of how the different
systems work. It is significant that during the recent floods
when we did mutually embed people my understanding is that it
led to a much better understanding of how the different organisations
work and enabled a much better service.
Q597 Lynne Jones:
I would like to explore the research issue and capabilities a
bit further. Are you actually bidding to take over responsibility
from the Environment Agency?
Mr Noyes: We have indicated what
our capability is and we think we are well placed to play an important
role, and we have made our submissions to the Pitt Review that
is underway at the moment. What Government decides to do we will
wait and see. We have indicated that we believe we have a very
important role to play and that our existing capability could
be better exploited than it is currently. In that sense, I guess
we are bidding but we are not saying that the Met Office must
do this . We are saying there is a lot of capability in the Met
Office that could be better exploited.
Q598 Lynne Jones:
We have to maximise our capability, obviously. I am referring
back to Dr West's comments earlier about defining vulnerability
and thresholds. He implied there was a lot of work that needed
to be done to get to that level. Could I ask the other witnesses
if they would like to comment on whether we are investing in that
capability and have we got the right set-ups to achieve what you
say we need to do?
Dr Calver: Can I clarify whether
you are talking about operational work or longer term research,
please?
Q599 Lynne Jones:
I think both, in actually predicting and we have a lot of research
being carried out by the Met Office in improving their predictive
capabilities. I am mystified at some of the stuff that you have
told us about this afternoon. I do not want even to try to understand
it, but I want to know that you are doing the work and that everything
that you think that we need is being done to respond as quickly
as possible to predict and to be geared up, both in terms of the
urban level as well and not just river and coastal flooding. Are
we investing in the capability that we need?
Dr Calver: I am only talking from
the more strategic research view and not the operational view
because I think that is beyond my remit. The important thing for
hydrological research is that any flood research is also done
in the context of other things that catchments are used for—water
resources, the requirements of the Water Framework Directive,
et cetera. Hydrology research, although it relates very much to
floods, also relates to other things. If you ask researchers whether
they need more money, there is always the great danger that they
will say "yes". Flood research is done in our organisation.
The Defra and the Environment Agency joint programme is a big
client and a big funder and I would say that was well developed
but could do with more funding. We are also funded by a Science
Vote through the Natural Environment Research Council and CEH
has a programme on water extremes, which includes flooding. I
do not really think I can comment on levels of Research Council
funding, except that we are always pleased if we get an increase
at Spending Review time.
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