Select Committee on Environment, Food and Rural Affairs Minutes of Evidence


Examination of Witnesses (Questions 101 - 119)

WEDNESDAY 7 NOVEMBER 2007

PROFESSOR EDMUND PENNING-ROWSELL AND PROFESSOR HOWARD WHEATER

  Q101  Chairman: Good afternoon, ladies and gentlemen, to a further evidence session in the Committee's inquiry into flooding. I would like to welcome Professor Edmund Penning-Rowsell, the Head of the Flood Hazard Research Centre at Middlesex University and Professor Howard Wheater, who is the Professor of Hydrology at Imperial College. Gentlemen, you are very welcome. Can I thank you in advance for the written submissions which you have both made. Professor Penning-Rowsell, I would like to start by inviting you to try and put our problem of flooding in the summer into some kind of context and perhaps compare the experience we had in this country with other flooding incidents, perhaps in a European context or perhaps, with thoughts of what is happening, sadly, in Mexico, in an international context. How serious was it?

  Professor Penning-Rowsell: How serious was 2007?

  Q102  Chairman: Yes.

  Professor Penning-Rowsell: It depends what you take as your metric of seriousness. Some people lost their lives, not very many fortunately; quite a lot of property was flooded, but not tens of thousands; there was a lot of dislocation of the local economy and people's lives in Gloucestershire and, to a lesser extent, further up the River Severn, but if you look internationally then the flooding problem we have in England and Wales is not as serious, for example, as that experienced in the United States of America, where regularly scores of people are killed each year as a result of flooding, which tends to have a different mechanism, largely driven by hurricanes and coastal storms. If you look at the Continent of Europe, the Netherlands is blessed with having no serious flood problem at all as a result of major investment since 1953; Germany has suffered serious flooding on the Oder and to a lesser extent on the Rhine. There is not a good database on the extent of flood problems across Europe, except the database in Belgium on loss of life, and this shows that in most cases most countries have a more serious loss of life from flooding problem than does England and Wales. So, in that respect, we are fortunate that many years of investment have mitigated the effect of flooding, and that has been the consistent policy of government right back to 1930. On the other hand, we are now experiencing greater dislocation, we understand, of our society as a result of the flood experience. This is a relatively new phenomenon and some features of the flooding in 2007 were certainly different from previous flood events. That does not categorically answer your question, except to say that I do not believe that Britain is amongst the foremost in flood affected countries and, certainly, if you look further afield to South East Asia, you will find countries such as Bangladesh where the flood extent is greater and the flood severity is greater. We do not even have in Britain the largest proportion of flood plain in the country. That is, again, in the Netherlands or Hungary. So, I would be cautious about saying we have a flood problem above the average in Europe and certainly not above the average in the rest of the world.

  Q103  Chairman: Again, to put it into context, you deal with flood risk management. If we take the different types, you made an interesting observation when you said that there were some different characteristics of the flooding this summer, I think, particularly with the urban dimension, because up to now most of the focus has been on coastal, river, estuarial flooding, but we had some other things that occupied our minds. In terms of order of priority, order of risk, the things that worry you as an expert, looking at the spectrum of flooding that we have in this country, what are the things that cause you the most concern? If you lose sleep at night on these matters, what might be the cause of that?

  Professor Penning-Rowsell: I do not lose a lot of sleep at night as a result of that kind of problem.

  Q104  Chairman: I presume you do not live in a flood plain then.

  Professor Penning-Rowsell: Quite close, actually. I think if I were to characterise the three most serious flood problems that I foresee in this country, they will be, firstly, a repetition of a 1953 type coastal flood event, although I think it will be true to say that the effect of that event will be far less than 1953, for reasons that I could go into. The second problem would be a repeat of the 1947 type event on the Thames, and there was a similar event in 1894 which is perhaps more serious, although it differs in different locations because there are large areas of the lower Thames catchment which are not substantially protected from flooding, particularly between Windsor and Teddington, and there a major event, such as a repeat of 1947, would cause tens of thousands of properties to be flooded and scores of thousands of people to have to be evacuated for upwards of a week and perhaps as much as a month. That is the second of my problems. The third of my problems would be a repeat of the 2007 event, and perhaps less the 1998 event, over a very large metropolitan city such as London: because if you had 100 millimetres of rainfall over London, as Gloucestershire had 100 millimetres of rainfall, you would have a much, much more serious situation. Those are my three worst scenarios.

  Q105  Chairman: In your evidence at paragraph nine you say, "The Environment Agency proposed, after the Boscastle flood, to identify the areas of highest risk to life from flooding. This study is urgently needed."[1] Have you got any idea why we have not seen any results of that?

  Professor Penning-Rowsell: No, you would have to ask the Environment Agency that. It is quite a complicated problem, but the flood mapping programme that the Environment Agency has undertaken was to have had a loss to life component to it, and some research was done by Hydraulics Research Wallingford in that direction. I do not believe it has been adequately followed up by maps or other types of information which would indicate areas where loss of life was more likely than elsewhere, and I think that is needed as an element of research which would help the Agency and particularly the emergency response organisations to cope more satisfactorily with the kind of events such as 2007.

  Q106  Chairman: I wonder if you can help us. You have taken us, if you like, into the forecasting and the probability side of flooding and we are humble politicians, we are not statisticians and we are not experts. You were talking about events almost on a probabilistic basis, but one of the things which we were alerted to when we did our report on the basis of the Foresight Report was the growing severity of an event as well as the question of the probability of things happening, and as lay people, we might be seduced by recent events to think that, to put it crudely, there are more big floods happening. In other words, they are happening with greater frequency and they seem to have to deal with more water. That is in its very crudest terms. Yet the concept of preparing for flooding on a frequency basis is defined in terms of events that occur one in 100 years, one in 150, one in 200, but they do not seem to talk about the severity of the event. In other words, I am not clear who defines what a one in whatever number of years' event it is; so how do you decide on the quotient of severity of the event and are we, with climate change, seeing the degree of severity starting to increase? Therefore, the third question that follows from that is, if any of those first two premises are correct, true or provable, what should we do about it?

  Professor Penning-Rowsell: That is a very complicated question.

  Q107  Chairman: That is why I put it to an expert.

  Professor Penning-Rowsell: Howard can deal with probability and I will have a few words on severity towards the end.

  Professor Wheater: I think the concept of a return period is very misleading. It is just a shorthand way of talking about probability. So, when we talk about a one in 100 year event, what we mean is we have got a giant dice and every year we throw that dice there is a one in 100 chance that in a particular year we will have a flood of a certain level of severity or greater. So, the scenarios for climate change we can talk about, but under certain scenarios in certain locations we expect the flood risk to increase, and that means that the chance of a large event will increase with time.

  Q108  Chairman: Let me stop you there, because that bit I understand: the rolling of the dice. That is, if you like, gambling basically. We have got gambling; we understand that. In terms of the event—just focus on the event—who defines the event? Who says what a one in 100 year event is?

  Professor Wheater: You can define it with respect to various criteria. You can choose those criteria.

  Q109  Chairman: Who does choose it though?

  Professor Wheater: It depends on the purpose for which you are doing an analysis, but the most common one would be the peak flow in the river, that is the highest discharge in terms of the amount of water moving down the river, so many cubic metres per second. That would be the most common criteria. Then what you would do is collect long records of data and look at the highest flow each year, and then you would look at the statistics of that and you would say, "Okay, that flow is a one in 50 and that flow is a one in 20 year event." If you were designing some flood protection, you might be interested in what happened when, say, flood walls were overtopped. In that case you might be interested in a certain volume of water above a certain threshold, and you could do the same analysis but your criteria then would be the volume over that threshold.

  Q110  Chairman: The reason I asked those questions is that we covered this in the short-term against a background of unprecedented amounts of rain falling in certain locations—Hull, Sheffield, Tewkesbury, for example—in very short periods of time (two days), getting effectively a month or more than a month's rainfall at one fell swoop. That is a pretty extreme event by our weathering. The question that had occurred to me is that, in terms of when you are modelling flood risk maps and trying to determine the policy decisions, Professor Wheater, to which you adverted a second ago, it comes down to the question now, when you are defining the event, as to how you should define it. So one of my questions is: taking into account the unknown variable of climate change but the reality of what we have had to deal with, do you think we need to fundamentally redefine these events and, against that background, re-examine, therefore, the effect that a redefinition of those events would have in deciding which areas are "at risk"?

  Professor Wheater: The simple answer is, yes. We have, in practice, a range of tools for looking at the statistics of floods. Traditionally those tools, which have been, incidentally, funded by Defra and MAFF, rely on climate stationarity, so they assume an unchanging climate. If we move into a situation with climate change, then we need a slightly different range of tools. One of the important contributing factors to flooding is how wet a river basin is before we receive the heavy rain. Typically, you find that flooding is most common in the winter because, although we do not have the highest rainfall intensity, we have the wettest catchments when the rain arrives. We then need to look in future climates at the combination of dry summers, let us say, and wet winters to see how the balance will play out. In terms of projections of the future, those are dependent on climate models, and those climate models are very good at getting temperature right for a global average. They are not very good at getting precipitation right around the globe—for example, they cannot get it to rain at the right time in the tropics—and when you come down to particular regions they are even more uncertain. So, you will find that if you look at a range of different climate models you will see quite a significant scatter of future impacts on rainfall. Basically, you need to recognise that uncertainty, run it through some hydrological models and then you can look at the range of outcomes. In fact, Defra and the Environment Agency have been funding research in this area to allow those kinds of rainfall scenarios to be developed and to provide the models that will allow the results to be generated. If I can touch on the issue of the observed data, it is very difficult to look for trends in both rainfall and flow data, particularly flow data, because there are lots of compounding factors—catchments change, people build houses, the land use changes, and so on—but there is really no evidence, to the best of my knowledge, from current observed records that flood risk is as yet increasing in the UK from observed flow data. If we look at rainfall, the picture is a little bit more complicated. Certainly there is evidence that over the past 30 years there has been an intensification of certain aspects of rainfall, but, on the other hand, 30 years ago it was a slightly drier than average period. So, within our immediate memory we have seen intensification but it is not clear that, if you look back one or 200 years, there is a real significant change of intensities.

  Q111  Chairman: So I do not misunderstand, Professor Wheater, what you said earlier on, you seem to agree with the view that we need to revise our current modelling arrangements and from the evidence I have read some people question whether we have sufficient data to make that decision, particularly in terms of what is the impact of climate change. What we have had is the Chief Scientist Foresight Report which postulates a number of scenarios of more intense weather conditions. So, that is a projection saying these are things that could happen, what we have is a series of events that have happened and we have, if you like, our short-term memory of look what happened this summer. Therefore, from a policy-making point of view, would you say that there is some solid ground to say, against that background, some of conjecture some of events, that we should revise our modelling and do we have the tools sufficiently well developed to make the kind of predictions that will ultimately guide the policy-maker? One would conjecture again that what you would have is that certain locations would become more risky to flooding and, therefore, the question is: what do you do about it?

  Professor Wheater: That is quite a complicated question. I think that there are significant uncertainties in modelling future climate, as you will appreciate. There are uncertainties about how the global community will respond in terms of future emissions, and so on. So, that is why there are various scenarios to try and scope out the range of possible futures and then within those scenarios the best tools that we have are models that try and represent the whole of the global climate system, and that is a pretty tall order. They can get some things remarkably right, so they do a great job in explaining what has happened to temperature over the past hundreds of years, but, as I said, rainfall is difficult and more complicated, and what you find is that the estimates of global climate models for rainfall are not very reliable. So, there are two ways forward to try and come up with better estimates. One is to improve the density of your simulation of climate over a region of interest, and so we have things called "regional climate models", which are high resolution. If you look at a global climate model, it averages the whole of the climate and the land surface over areas of the order of 300 by 300 kilometres, which is very coarse. You get a few grid squares over the whole of the UK. If you can nest a fine resolution model within that global model, you can come back to a grid that is maybe of the order of 40 kilometres, 50 kilometres, something that is still a bit big but more useful. There are limitations to that, because you have to take the boundaries from the coarse model, feed them into the fine model and within the fine model you cannot represent all the feedbacks and the oceans, and so on, but that is one set of tools that you have in your tool box. The Hadley Centre has a range of regional climate models which it is using for looking at future climate scenarios. The other approach is to say, there are certain things in climate models that we can believe more than others—those are things like temperature, pressure and humidity—and we can take those pieces of information and use them to drive statistical models that will then allow us to generate possible rainfall sequences for the future, and that is one of the lines that is being funded in the UK.

  Q112  Chairman: Let me finally, before I pass on to Mr Drew, ask you this question. You have analysed some of the challenges using predicted models. What we saw this summer in two days was a month's rainfall. Do we have models whereby you could say, very crudely, "Okay, I am going to apply that scenario uniformly across the whole of England and just see what it throws up in terms of flood risk"? Could you do that?

  Professor Wheater: It could be done, but it would be difficult, in the sense that the way in which the UK is modelled is on a region by region basis and to inconsistent levels of detail, but it could in principle be done.

  Professor Penning-Rowsell: The Foresight Report was not too far away from what you have just said, which in a sense dumped a whole belt of flooding over the whole country, not related to catchments but related to grid squares, and looked at the consequences.

  Q113  Chairman: I think there was an element of surprise in Sheffield, for example, about what happened. In terms of trying to identify where serious flooding might in theory occur and, therefore, what the implications would be, certainly looked at from the layman's point of view, I would say if you could apply these things universally, what pops up? Bearing in mind you have got concentrations of population, is that kind of approach any use whatsoever in helping you to decide your future flood protection analysis, or is it just an interesting statistical game but without any sort of reason to it?

  Professor Penning-Rowsell: That is exactly what the Environment Agency is doing through its catchment flood management plans: a slew of programmes to look at each catchment in turn to look at exactly what you are suggesting. Where are the hot spots? Where are the real pinch points? Where would investment be best directed? At a strategic catchment level. That is something that has been done over the last five or six years and that has given us a view of the country which we did not have before.

  Q114  Chairman: To conclude then, does that process need in any way further refinement or further investment to improve the quality of its outcomes?

  Professor Penning-Rowsell: Probably.

  Professor Wheater: Yes, I think that---. Well, we can think about modelling at different scales. There is work at the moment being done, for example at the Centre of Ecology and Hydrology, funded, I think, by Defra and the Agency, which is looking at a set of small catchments over the UK, running different climate scenarios and seeing what the responses are. When we work with the bigger catchment systems, it is a more complicated modelling task because we have to consider the interactions of all the contributing areas and the way in which floods are routed. At the moment in the current stage of catchment flood management plans, that is being done in a relatively simple way which is not very amenable to looking at climate change. We actually need an improved generation of models to allow us to simulate these responses continuously so we can incorporate the dry summers and the wet winters and then determine the outcomes.

  Lynne Jones: We had a submission from Professor Knight, who was very critical of the Environment Agency's expertise and also of their modelling.[2]

  Chairman: Would you like to remind us who Professor Knight is?

  Q115  Lynne Jones: Professor Donald Knight from Birmingham University. He criticised the over-reliance and the bias towards hydrology and the lack of consideration of hydraulics and hydrodynamics. Maybe your response is, "Well, he would, would he not", I do not know. He also says that there is a lack of in-house expertise within the EA and is critical of the fact that there is no chief engineer and also says that the 20 per cent rule is very much an underestimate. Would you care to comment?

  Professor Wheater: Yes, there are two aspects of flood generation really. First of all, how much water is going to get into your river and then what is going to happen to that water as it moves down the river system? The area that Donald Knight has been referring to is the movement of water down the river system, and the hydrological problem that he refers to is how much water is going to run off from the land into the river system. So, of course you need to understand both problems, but the chances are that you can go very badly wrong in estimating the amount of water that gets into the river and, if that is the case, it does not matter how good your river routing model is if you have got the wrong amount of water in it. For me, speaking as a hydrologist who is interested in the run off, I think the biggest question is how much water is going to arrive in the river, and then the second question, how is that going to transmit downstream? The question of expertise in that area: I think that probably there is not a large amount of expertise within the Agency on the particular problem of river hydrodynamics. However, the Agency does a lot of work through consultants who are well qualified in those areas and have models which are developed to a high level and applied widely, not only in the UK but overseas. So they have expertise that they can call on without having particular scientific expertise on the nitty-gritty of the computer code of those models.

  Q116  Lynne Jones: You think that is adequate, because certainly Professor Knight does not. He criticises it for outsourcing all its hydrodynamic modelling?

  Professor Wheater: I think that there is a generic issue really about how much work an organisation like the Environment Agency does in-house and how much it subcontracts.

  Q117  Lynne Jones: I think it is concerned with the lack of continuity that you can have people involved on an ad hoc basis rather than having the in-house expertise on a long-term basis?

  Professor Wheater: Yes. I think that it is difficult for people who are purely managing external programmes to really keep in touch. In an ideal world one would have some in-house expertise that is actually working on the problems and, hence, has a real in-depth understanding of them, and I think in this area that is not something that the Agency has at the moment. I think the Agency, in terms of its science programme, has been through quite a lot of changes. It used to be, going back ten years or more, that science was organised in a fairly ad hoc way, but then they developed in my mind a rather good programme of developing centres of technical expertise, but in recent re-organisations those centres have been disbanded and the expertise is managed in a rather different way. I am not entirely sure what the current status of the Agency science programme is because I know it is undergoing fairly radical change at the moment.

  Q118  Mr Drew: Can I take Professor Penning-Rowsell back to his paper to start with, but it does relate to what I want to ask you about. You said post Boscastle the Environment Agency were going to identify these areas of highest risk of flooding. Is not that what the flood maps already do? I accept that Norwich Union would argue their maps are better than the Environment Agency's, and there may be some justification for believing that, but how much more information can you give people without effectively either worrying them to death or accepting that these areas have such a risk that you would not want to situate additional development there?

  Professor Penning-Rowsell: There is a balance to be struck there. The comment on paragraph nine is about information of risk to life from flooding, and that has not been followed through by the Agency in a way that I think needs to be done.

  Q119  Mr Drew: Can you do that?

  Professor Penning-Rowsell: Oh, yes. We are getting much more research and intelligence about the factors that lead to loss of life in floods. In general terms it is to do with the velocity of flood waters, it is to do with the depth of flood waters and it is to do with the vulnerability of people who might be exposed to flooding. So in areas of substantial water depth where velocities are large, the risk of loss of life is much more obvious, much more apparent, much more real than right at the edge of the flood plain where velocities might be quite low and the flood water might be quite shallow. So there is gaining intelligence about the factors that lead to loss of life. It is not a perfect science by any manner of means, because sometimes loss of life from floods is a function of the behaviour of the people involved rather than the flood itself, but the Agency has commissioned research under the Defra, EA Research and Development Programme to look at this and some algorithms have been produced which could result in maps produced by the Agency within its flood plain mapping programme, which is relatively unsophisticated in the sense that it is for public consumption and it is not in very great detail. It is the kind of thing you can look up on the web for your own house and see whether it is blue or whether it is turquoise, indicating a flood or a serious flood. It does not go further than that, although it does differentiate between areas that are defended or not, but it does not say this is a very serious flood, with high velocities and lots of deep water around, as it might do for Tewkesbury or for Oxford or for the coastal locations. It does not do that. That is the point we are making under paragraph nine.


1   Ev 35 Back

2   Ev 462 Back


 
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