Ready for winter – new flooding communications programme

The Scottish Flood Forecasting Service (SFFS) will have another outlet for its flood guidance activities this winter.

The Scottish Environment Protection Agency (SEPA) is launching a campaign to provide the public with advance notice of potential flooding. Through a newly created suite of winter marketing materials and a strategic approach to communicating, this campaign will be able to more accurately target communications activity to those at risk of flooding. It will also be able to provide up to 3 days’ notice of potential flooding, giving people more time to prepare and take action.

An example of one of the messages to be posted in response to a forecast of possible flooding.

In order for this campaign to be accurate and effective, SEPA’s Flooding Communications team will work with the SFFS, to monitor the likelihood and impacts of flooding. If significant or severe flooding is imminent, the campaign will be activated and messages will be broadcast to the areas at risk. Messages will be advertised on both national and local radio stations, on social media and online and will also be shared with key partners and flood action groups for further dissemination.

The communications activity will complement SEPA’s Floodline Service, which provides free messages to customers when SEPA issues a Flood Alert, Flood Warning or Severe Flood Warning in their area, and will encourage more people to sign up to the service.

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Summer river flooding in Scotland

It had been a fairly quiet few months for the operational side of the Scottish Flood Forecasting Service, before heavy rain struck much of the country at the start of June, causing some significant flooding in the north east, and minor flooding in many other locations. Forecasts consistently indicated low pressure and ‘wrap around’ feature bringing heavy rain to the north and north east in particular, though there was some variation from forecast to forecast as to the exact location and rainfall amount forecast, as shown in Figure 1.

Figure 1: Peak 24 hour rainfall totals forecast on Sun, Mon and Tues for Tues 6/ Weds 7 June

The Grid-to-Grid model also highlighted this uncertainty, though it was clear that all scenarios would lead to much higher than usual flows (particularly for the time of year) in some areas. See Figure 2.

Figure 2: Grid-to-Grid forecast on previous day and range of forecasts for River Narin

Figure 3: Area of Concern map for Tues 6 June Flood Guidance Statement

To reflect the uncertainty the Flood Guidance Statement indicated a low likelihood of significant flooding, with an Area of Concern map. See Figure 3.

 

 

 

 

In the event, over 100mm of rainfall in 24 hours fell in some areas, and some rivers exceeded flooding levels, particularly in the north east. A number of Flood Alerts and Flood Warnings were issued. Some properties were evacuated and the Inverness to Aberdeen railway line was flooded. Surface water flooding issues were also widespread.

Figure 4: Portsoy in Aberdeenshire (photo from The Scotsman)

Perhaps the most interesting aspect of this event is that even in summer, and following a prolonged dry spell, river flooding is always a possibility during a prolonged rainfall event. Whilst surface water flooding did occur, the main focus was on the rivers.

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Snowmelt forecasting capability within Grid-to-Grid

The formation and melting of snow can be a key component of river flows in the UK, particularly in upland areas. Different configurations of the countrywide Grid-to-Grid (G2G) model are used to deliver the snowmelt component, using different approaches for Scotland; and England and Wales. The Scotland configuration used by the forecasting service uses the G2G Snow Hydrology scheme with Numerical Weather Prediction (NWP) model inputs of precipitation and air temperature at screen-height to form and melt the snowpack. In contrast the Flood Forecasting Centre (FFC) in England and Wales uses NWP parameters to split precipitation into rain and snow; and the Joint UK Land Environment Simulator (JULES) to estimate snow melt as an external input to G2G.

We have recently taken delivery of a review of the two methods, in a project jointly commissioned by the SFFS and FFC and carried out by the Centre for Ecology and Hydrology (CEH). The report reviews the snow hydrology methods, describes the operation of the two methods, looks at ways to improve them, and carries out comparisons between the two methods. Some examples of the output are shown below.

g2gzones

Comparison of current model configuration with a trial process in which the 1km grid cells are represented by a series of elevation zones. The differing amounts of snow melt in each zone are then recombined to calculate the grid cell run-off. It was found that the new method made little difference at the catchment scale – this example is for the River Muick at Invermuick.

G2Gwsnow

Modelled flows for the River Spey at Boat o’ Brig using various snow module formulations.

The study confirmed that modelling snow processes generally improves performance, irrespective of the particular snow formulation used. A structured comparison of the two methods currently in use, alongside other formulations, shows the NWP-JULES method currently outperforming the G2G Snow Hydrology (G2GSH) module. This difference disappears when a revised parameter set for G2GSH based on a more extensive hydrometric data record is used. There is still substantial river flow uncertainty at the catchment level, however, with peaks being over- or under-predicted.

Comparison of streamflow modelled from different snowmelt methods. G2GSH is current Scotland methos. G2GSH-new is recommended new calibration. NWP-JULES is current England and Wales method.

Comparison of streamflow in Scotland modelled from different snowmelt methods. G2GSH is current Scotland methods. G2GSH-new is recommended new calibration. NWP-JULES is current England and Wales method.

 

As well as providing useful insights into how the model is performing, some recommendations were made. In the short term, new parameters for the G2G snow hydrology scheme could be implemented in time for next winter, to provide some immediate improvements. Longer term, more work is required on validation through snowpack monitoring and also on quantification of uncertainty, using NWP ensembles. The applicability of the NWP-JULES method used in England and Wales should also be considered.

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EFAS annual meeting in the Netherlands

Louise Parry recently attended the annual EFAS Partners meeting on behalf of SEPA and the forecasting service. She sends the following report.

In March this year the Annual European Flood Awareness System (EFAS) Partners meeting took place in De Bilt, near Utrecht, in the Netherlands. EFAS is a European Commission initiative set up by the Joint Research Centre (JRC) of the European Commission, to which SEPA (and the SFFS) became a partner in 2015. Access to EFAS is of operational benefit to the SFFS duty hydrologists as it is a complementary and added-value service to our national forecasting system, helping to increase preparedness for fluvial floods by providing a regional forecast up to 10 days in advance.

SFFS poster at EFAS

The annual meeting is an opportunity for the partners to feed back information on EFAS performance over the last year, as well as for the EFAS scientific community to update the partners on new developments in the EFAS service. The last 12 months have been relatively quiet in Scotland in regards to fluvial flooding (thankfully!), therefore there was little to be fed back to EFAS in terms of their performance. However, areas of the UK have suffered flooding from other sources, in particular from surface water (pluvial) flooding, which is an extreme challenge to the forecasting community due to the highly localised nature of the events in contrast to the resolution of the forecasting models. However, both the SFFS and our England and Wales cousins, the FFC, have models and tools which help the forecaster assess the risk of a surface water flood event occurring. Therefore, we (the SFFS) decided to collaborate with the FFC again this year, to produce a feedback poster with a twist, giving the requested feedback, but also detailing some of our approaches to surface water flood forecasting. This created the opportunity for scientists and forecasters from other nations to ask questions regarding our methodologies and prompt discussion on ideas for future developments. This exchange of experiences and ideas for development is what I believe to be one of the key benefits of the EFAS community and the annual meeting.

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Storm Frank On Tour

Operationally it has been a fairly quiet last 12 months or so for the forecasting service. The interest in the events of winter 2015-16 still continues, however, particularly the floods resulting from Storm Frank at the very end of 2015. Recently members of the forecasting service presented aspects of our work surrounding this event, at two different events in Edinburgh.

Karen Pinkerton explaining her poster on Communicating Storm Frank

On 15th March Karen Pinkerton presented a poster at the Royal Society of Edinburgh conference ‘How can we learn to live with floods?’. The poster looked at our forecasts in the run up to the flood events, and how the flood guidance produced by the service influenced the emergency response, in particular in Dumfries and Galloway. It emphasised the importance of early communication.

 

 

 

 

Then on 21st March, Louise Parry and John Mitchell gave a talk to the Royal Meteorological Society entitled ‘Forecasting Storm Frank’. This very much focussed on the science behind forecasting both the meteorology and the hydrology.

Louise Parry and John Mitchell at Royal Met Soc

Each presentation illustrated a different side of the critical work done by the service during flooding emergencies – both the science and the service, neither of which could be effective without the other.

 

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Hydrologists make the water go round – BHS international conference

I recently attended the 2016 international conference of the British Hydrological Society, at Cranfield University. There were a number of broad themes, including flood risk and water resource management, with most of the first day being given over to presentations on the UK floods of December 2015 and January 2016. Topics included real time modelling, post flood modelling analysis and discussion of return periods, in particular whether it is plausible to have several floods of return period 100 year+ over a single decade, or whether in fact such clustering is part of the natural long term cycle.

The majority of presentations looked at the floods from the perspective of northern England, so my talk on the impacts in Scotland of the flooding from storms Desmond and  Frank and the work of the Scottish Flood Forecasting Service, provided a different viewpoint. SEPA’s Nigel Goody (below), past president of BHS, also looked at the destruction wrought in Scotland, in particular on our hydrometric capabilities, providing a warning about the huge uncertainties involved in measuring these sorts of events.

The full programme of the conference can be found at this location.

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High Impact Weather and Climate Conference

High Impact Weather and Climate was the subject of the conference held by Royal Meteorological Society and National Centre for Atmospheric Science at the University of Manchester last week. Members of the forecasting service attended, along with many colleagues from the Met Office, universities and other practitioners. The three days were split into three broad topics – Observing, Predicting and Responding, and included key note speeches and a number of workshops, as well as poster sessions. The over-riding theme was that of impacts – how do we know when they are happening, how do we forecast them, and what is the best way to communicate this to those who need to know?

Liz Bentley from RMetS introduces the conference

Liz Bentley from RMetS introduces the conference

The observations talks and workshops centred around the seemingly simple question – how do we know what is happening? High quality observation networks are sparse, so the point was made that crowd sourcing data, whether on weather or impacts, is a potential way forward, with an acceptance that the quality of individual observations may be less than ideal. Initiatives using smartphone technology, the Met Office WOW  site, and SEPA’s Report A Flood  are examples of this. The nature of observations was also questioned; particularly at the extremes, modelled parameters may be just as valid as ‘observed’ – Met Office Chief Scientist Prof Julia Slingo made the interesting point that an observation is just one particular version of reality.

(L) Mike Cranston discusses the Flood Guidance Statement during the 'Perfecting the Weather Warnings' workshop. (R) Louise Parry discusses the SFFS poster with Steve Cole from CEH.

(L) Mike Cranston discusses the Flood Guidance Statement during the ‘Perfecting the Weather Warnings’ workshop. (R) Louise Parry discusses the SFFS poster with Steve Cole from CEH.

Workshops such as those focussing on the Hazard Impact Model  and the Flooding from Intense Rainfall  projects presented the latest thinking in impacts modelling – the latter drawing on the work done for the Glasgow surface water flooding model  in 2014, as illustrated in the SFFS poster.

On the response side, the challenges ahead were presented in an excellent talk by Virginia Murray centred on the Sendai Framework for Disaster Risk Reduction , the ultimate aim of which is provide access to early warnings for all people by 2030. Currently 80% of developing countries have only basic or no warnings systems in place. Sally Priest, from the Flood Hazard Research Centre , made the point that just sending people a warning doesn’t necessarily lead to them taking action – people don’t always understand the warning, trust the authority, or act rationally. Care is particularly needed when communicating probabilistic warnings, the subject of a workshop involving the forecasting service, with partners at the Met Office and Flood Forecasting Centre. We played the Game of Making Decisions Under Uncertainty (developed by Micha Werner, to be available at the link soon) in which delegates were invited to make play the role of business owners and make cost-loss decisions based on probabilistic forecasts of flooding, and also discussed the situations in which low probability high impact warnings should take precedent over higher probability low impact situations. Even within the forecasting community there are many varying opinions on this topic.

The other benefit of the conference was the opportunity to meet and discuss topics of interest with colleagues from other organisations, progress existing projects and lay the groundwork for future collaborations.

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