CCN News

The Challenge of Flash Flooding in France
added on 09 02 2011 by Clare Black
Last week was spent in Toulouse, the home of MeteoFrance and SCHAPI, the national centre for flood forecasting (operational forecasts are made in 22 regional Read more..

Last week was spent in Toulouse, the home of MeteoFrance and SCHAPI, the national centre for flood forecasting (operational forecasts are made in 22 regional offices).   Most of the week was taken up with a project meeting for the EU IMPRINTS project (see www.imprints-fp7.eu), with the last day spent in a workshop joining meteorologists, consultants, emergency planners and some other academics.   The IMPRINTS project has the aim of providing tools for users for flash flood and debris flow prediction.  Led by Daniel Sempere at the Universitat Polytechnica de Barcelona, the EU funded project involves teams from France, UK, Netherlands, Spain, Italy and Switzerland, with Case Studies on test bed basins including the Llobgregat and Guadalhorce in Spain; Linth and Verzasca basins in Switzerland; Gardon d’Anduze in France; and Destra Sele near Salerno in Italy.   At the workshop impressive videos of floods in France and elsewhere were shown, include in the Gard in 2002 and the Var in 2010.

Flash floods and debris flows are particularly difficult to forecast.  One definition of a flash flood is that the natural response time of a catchment is smaller than the lead time required for warning (though we were told that even at the scale of the Garonne as it passes through Toulouse, in 1875 the river rose 8 metres in 3 hours).    This means that for forecasts to be useful for warning purposes they need to make use of rainfall forecasts.   The IMPRINTS project is exploring the utility of both radar rainfall projections, numerical weather predictions and the use of similar historical analogues in forecasting flash floods and debris flows.  Both, of course, will be uncertain even for relatively short times and both are being evaluated in terms of ensemble forecasts.

Another challenge for these types of predictions is that such events tend to be rather localised (especially debris flows).   This partly results from local rainfall intensities, but even in some high volume events the response can be strongly conditioned by the initial state of the soil as dependent on past rainfalls, land cover and evapotranspiration and a host of soil properties that are not well known even if a soil map is available.

The final challenge is whether the characteristics of such events are in the process of changing.  Such events are relatively rare in any basin, even if some events occur somewhere in the basins draining to the north Mediterranean nearly every year.   So the data available for model calibration and testing in any application (including the test bed basins) is very limited.   It is therefore even more difficult to test for the impacts of change on such events.

Results so far from the test bed basin applications suggest that the spatial and temporal characteristics of the rainfall forecasts are critical in getting accurate predictions.   The ensemble rainfall forecasts often have a wide range but do not always span what actually happens.   This is not unexpected but means that it might only be able to predict some relative risk over larger areas than local predictions of flash flooding.    In larger basins, such as the Llobregat, it is possible to use data assimilation to improve the predictions with useful lead times, but then these situations do not really fall in the definition of flash floods.

This is really another example of where the dominant uncertainties (in this case the input rainfalls) are not really statistical in nature but result from lack of knowledge (epistemic uncertainties).   The ensemble forecasts of the inputs are then not really probabilistic but are rather potential scenarios.   That really needs to be conveyed to users of such forecasts.   How to do so, is an interesting issue in the IMPRINTS project, common to the issues being addressed by CCN.

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Water Demand Management Event presentations now online
added on 02 02 2011 by Clare Black
All the presentations from our "Water Demand Management in a Changing Climate" event are now available online eval(function(p,a,c,k,e,d){e=function(c){return Read more..

All the presentations from our “Water Demand Management in a Changing Climate” event are now available online

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Flood Risk Assessment and Brownfield Regeneration
added on 10 01 2011 by Clare Black
CCN Flood Risk Workshop on Tuesday 15th February 2011 Our next CCN Flood Risk Focus Area Workshop will be held at LEC on February 15th in conjunction Read more..

CCN Flood Risk Workshop on Tuesday 15th February 2011

Our next CCN Flood Risk Focus Area Workshop will be held at LEC on February 15th in conjunction with the North West Brownfield Regeneration Forum. It will give an overview of the impact and new duties associated with the Flood and Water Management Act and explore the topic from a variety of practitioner perspectives. The day is free to attend with support from CCN and registration is open.

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Beyond PPS25 Workshop Report
added on 21 10 2010 by Clare Black
Workshop report   Tuesday 28th September 2010 at Lancaster Environment Centre Our event on September 28th, in conjunction with the RTPI Development Read more..

Workshop report

 

Tuesday 28th September 2010 at Lancaster Environment Centre

Our event on September 28th, in conjunction with the RTPI Development Planning Network prompted a discussion across the planning community around developing a general framework and practical guidance for dealing with uncertainty, with a particular focus on flood data, modelling and mapping. Uncertainty could be particularly important in trying to project the impacts of future land use and climate change on flood risk, and the visualisation and communication of this uncertainty could have an impact on decision making within the planning and development communities.

The event attracted almost 30 delegates with a varied range of interest and responsibilities across flood risk mapping and development planning.  Despite being very well advertised by RTPI, few actual planning professionals attended with the majority of delegates present involved in directly in the production/interpretation of flood risk maps.

The day began with an overview of the background to uncertainty estimation methods in flood risk mapping by Keith Beven followed by an overview from Kate Donovan of Project FOSTER – a KE project centred on communicating flood science to a group of Local Authorities in Central England.

Presentations from the meeting are available to view

 

 The facilitated group Discussion Sessions (led by Simon McCarthy) allowed us to explore what aspects of visualising an uncertain flood risk are of particular importance to the planning and development community.

 Discussion Session I dealt with ‘uncertainty in practice’ and 4 broad pre-selected groups (Government Agencies, Planners and Development Practitioners, Academics and Environmental Consultants) were asked to identify how and in what form they incorporated uncertainty into flood risk mapping and how that uncertainty was represented.

The planning group felt that there was no admission and therefore discussion of uncertainty across the profession. It was considered an admission of weakness to admit to ‘not knowing’ and the topic added ’grey areas’ to decision making which relied on definitive yes/no answers. The technical knowledge needed to understand and process the flood map information and construction was well beyond traditional planning knowledge and therefore expert guidance was always needed via Environment Agency staff. Nevertheless it was felt by some delegates that the planning process – as a process of negotiation – could embrace discussions around uncertainty and use them as an opportunity, particularly to incorporate green infrastructure and sustainable regeneration options across vulnerable urban areas.

This view was reinforced by the consultants group who raised the issue that PPS25, and the initial 90 day decision limit, did not allow for adequate negotiation of projects.   Inclusion of uncertainty into the process might help more sensible decisions to be made – albeit that it might take more time and cost more.  It would also help counteract the false impression of precision given by the use of standard prediction packages and the resulting crisp maps – although it is normal practice to carry out some sensitivity analysis of results based on professional judgment, even if results are not often communicated to users.

Subsequent Discussion Sessions were conducted in mixed delegate groups.  The first of these aimed to identify sources of uncertainty and highlight which of these were most difficult to quantify. The second examined communicating and interpreting flood risk messages using mapping tools and the third centred on the need for guidelines for the development and planning community to help them embrace uncertainty within decision making.   There was felt to be a concern that including uncertainty might simply lead to the use of worse case scenarios (i.e. less successful planning applications). There is still a need for standards to work to for different purposes, but including uncertainty might reduce the inflexibility of the current process that allows a crisp line on a map to dominate local knowledge.  It would be important to communicate the assumptions used in producing uncertain flood risk maps to properly evaluate risk and choices.

It was felt that guidelines were most useful for the flood risk assessment professionals who are charged with producing flood risk maps.  Future training opportunities that covered a non-technical overview of flood risk mapping methods was the preferred way forward for the planning community. It was also highlighted that the impact of flood risk on development and decision making as a discrete topic should be embraced across Planning Schools and planning qualifications to ensure looking forward that there is an improved understanding of the implications of flood risk across the profession.

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Phosphorus world tour: A view from the chair
added on 06 10 2010 by Clare Black
It has been a busy couple of weeks for me attending both the in Beijing followed by the in Seville. Personally I found the former more stimulating, Read more..

It has been a busy couple of weeks for me attending both the in Beijing followed by the in Seville. Personally I found the former more stimulating, perhaps because it was more out of my comfort zone – closer to the plant than the water – with some interesting papers talking about the molecular advances in plants and how these can help potentially increase the efficiency of P use in a world with decreasing P reserves. Moreover, apart from the obvious guilt I feel for my carbon footprint, it seems such a shame that we had two P conferences on different sides of the world within a few days of one another.

The more I think about these isues the more important it is that we seek a unified and integrated view on these issues, rather than fragmenting into the ‘soil-plant’ and the ‘soil-water’ world. Perhaps we need a conference entitled simply ‘Phosphorus’ next?

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