New coastal flood forecasting system for Eilean Siar goes live!

This week sees the launch of two new Flood Warning schemes by SEPA. One is a scheme addressing fluvial flooding in Aberfoyle, in the southern Highlands. The other, discussed here, is for the Outer Hebrides (also known as Eilean Siar in Gaelic). The scheme has been developed over the past year or so and presented a number of forecasting challenges. 

Eilean Siar/ Western Isles

The Outer Hebrides consist of around 60 islands, of which 15 are inhabited. Many of the islands are linked by causeways. The coastline is complex, with many inlets, small islands and sand bars. The weather can be extreme (for the UK), with the west coast fully exposed to Atlantic storms. Travel around the islands is often severely restricted due to flooding of causeways by high water levels or wave action.

L: Baleshare causeway 2020. R: 2014 event in Stornoway

A forecasting system was developed for the islands in a project supported by coastal modellers at JBA Consulting, for use in SEPA’s Delft FEWS flood forecasting platform. It involves still water level (SWL) calculations for 44 forecast points, and automated look up tables to calculate overtopping rates, these rates being generated from offline modelling. In partnership with the Met Office, tidal surge, wind and wave short term forecasts are added to long term astronomical tide series to determine the values at the forecast points, which are compared to warning thresholds derived during the project.

Schematisation of the forecasting system. Image from JBA Consulting

The scheme was launched on 10 November 2020 and will deliver flood warnings to emergency responders and members of the public. The current forecasting outlook suggests it’s likely to produce forecasts of exceedance over the coming days.

Image from FEWS Scotland showing possible threshold exceedance using ensemble level forecast

Messages will be issued via SEPA’s Floodline service, as appropriate. Forecasts will also inform the coastal risk assessment for the forecasting service’s Flood Guidance Statement.

Launch of this new system is another milestone in our aim of working with the Met Office to extend flood warning lead times and understanding uncertainties in forecasts, through the use of ensemble forecasting.

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Exploring an impact-based approach to flood forecasting

As we’ve previously reported on here, many parts of the North and West Highlands of Scotland can be spared major flooding impacts even when significant rainfall (100 to 200 mm) can fall.

In October 2018, although the town of Oban was impacted by localised flooding, many areas were spared more property flooding. Likewise in March 2015, a hydrologically significant event across much of the Highlands again only led to minor property flooding. However, it’s often the road and rail infrastructure that is most significantly impacted by these types of events as we recently observed.

A frontal wave affecting parts of western Scotland overnight on the 12 and 13 September brought with it strong winds and orographically enhanced rainfall across the mountains.  Quite widely 50 to 60 mm of rain was recorded with peaks of 80 to 120 mm recorded across Skye and Lochaber.  The forecast (see below) was for widespread minor flooding to occur, but the guidance also suggesting a very low likelihood of more significant impacts.

The Area of Concern as issued by the Scottish Flood Forecasting Service on Friday 11 September

During the Sunday morning reports started to materialise of major disruption across the transport network. Impacts included flooding and disruption on the Crainlarich to Fort William rail line at Bridge of Orchy and flooding of main trunk roads including the A890 and A82 in Skye and Lochaber and the A8 in Renfrewshire.

Attempting to link our forecasting capabilities with the transport receptors is the focus of a new area of work for us.  In partnership with Transport Scotland, we’re now exploring ways of developing an impact-based forecasting approach for the Trunk Road network in Scotland. 

The research will look at how best to predict the impacts of flooding across the vulnerable parts of the transport network and explore whether empirical links are sufficient or whether these links need to be developed through pre-simulated scenarios as set out in the recent research on towards improved surface water flood forecasts in Scotland.

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Operational Forecasting Across the Globe: Sharing Science at EGU20

For several years the ‘operational forecasting and warning systems‘ PICO session has been a popular feature of the EGU hydrological sciences program.  However, with restrictions on travel and meetings in place due to Covid-19, the whole of the 2020 Assembly took on a new form – virtual. #shareEGU20 was a week long event taking place over the first week of May and freely available for anyone to join. Over 18,000 abstracts were published with 63% being presented virtually through various online displays, all of which were supported by over 200,000 discussion point or messages being posted by the virtual delegates.

As for the operational forecasting session, alongside the abstracts, 12 displays were presented with 120 people joining the discussion. To help with the facilitating, the conveners connected via video conference between New Zealand, Sweden, the Netherlands and Scotland to steer the presenters and discussion.

The diverse range of operational forecasting systems that were presented, included the implementation of an impact-based forecasting system in Barbados (University Corporation for Atmospheric Research, US) to experiences of co-developing flood forecasting in West Africa (Jafet Andersson, SMHI, Sweden).

Speight et al

Display on ‘Reviewing operational and near operational progress in surface water flood forecasting for urban areas’ by Linda Speight (University of Reading)

Co-convener Céline Cattoën-Gilbert (Hydrological Forecasting Scientist at NIWA) offered her highlights of the session: “Advances are being made in real-time inundation forecasting at national, regional and urban scales. For example, Linda Speight (University of Reading) presented an overview of the latest science, tools and approaches available for monitoring and forecasting flood impacts to inform future developments for the Scottish Environment Protection Agency (SEPA). With empirical-based threshold scenarios, hydrological forecasting chains linked to pre-simulated impact scenario for national or regional scales, or linked to real-time hydrodynamic simulation at the urban scale, there is not a one size fits all solution – a reflection of different decision-makers’ needs. The work presented by Alessandro Masoero (CIMA Research Foundation) follows the last approach by building an early warning system in Guyana at the national scale with real-time hydraulic inundation forecasts at selected locations. The adoption of real-time inundation forecasting approaches will require strong interdisciplinary efforts to support informed decision-making.”

As for the presentation on surface water flood forecasting, the delegate discussion focused on: whether there was a focus on a means of communicating the forecasts; on how pre-simulated impact scenarios compensate for the absence of real time modelling; and whether there were attempts to link these to crowd sourcing of information. More on this research and how scientists are tackling surface water prediction in this Conversation article from December 2019.


World-wide hydrological predictions using the HYPE model by SMHI as presented by Pechlivanidis (SMHI)

Ilias Pechlivanidis (Scientific Leader in Forecasts of Water Variables at SMHI) and another co-convener, said “a big effort is currently  given on setting up early warning and climate services at the large scale with the objective to address local needs. Among the various interesting studies, Katie Smith (CEH) presented a proof-of-concept global hydrological outlook system developed by many international partners to increase resilience to hydro-climatic risks. The system is setup for the WMO under the HydroSOS topic to provide an overview of historical and forecast hydrological status. My co-author Jafet Andersson presented a number of operational hydrological forecasting services with applications in European, Niger river basin and global domain. The services provide information at medium-range, sub-seasonal and seasonal time horizons, whilst strong user engagement was followed in the co-design of the services addressing further the local user needs.”

CEH water resources

The UK Water Resources Portal as presented by Lucy Barker (UKCEH)

Current talk of a potential drought in the UK links well to the presentation by Lucy Barker (UKCEH) on dynamic real-time hydrological status monitoring in the UK. Lucy’s presentation highlighted how understanding the current hydro-meteorological situation is critical to manage extreme events and water resources, illustrating how a new portal has been developed to enable dynamic, interactive, real-time access to hydro-meteorological data. This article highlights how the tool is providing a hydrological outlook for the current situation. There were other abstracts that were contributed and all of these and the displays for this session are available on the EGU20 pages.

Yes, I’m sure we’ll all admit to missing sharing stories and capabilities in the more familiar surroundings of the Austria Center Vienna, but has #shareEGU20 set a new benchmark in conferencing?

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Royal Meteorology Society Award for the Scottish Flood Forecasting Service

Scientists from Met Office and SEPA working within the forecasting service have been recognised at the Royal Meteorological Society Awards for their work on the ‘Surface Water Flood forecasting in Urban Communities’ project. They, along with their colleagues from The James Hutton Institute, CEH Wallingford and CPAESS – UCAR, USA, received the Innovation Award which is based around innovation in meteorology, with a particular focus on business and/or public impact. It recognises people, projects or programmes within the academic, scientific or business communities who have made significant contributions to educating, informing or motivating organisations in their response to meteorological challenges. The full list of award winners can be seen here.

Example output from the surface water impact model for Glasgow

We reported on the project in a number of blog posts around the time of the initial project in 2014. A probabilistic surface water impact forecasting tool was developed for central Glasgow and used operationally during that summer’s Commonwealth Games. The model is still in use by the forecasting service, and the principles behind it have since been applied elsewhere in the UK.


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Scottish Flood Forecasting Service Annual Report

This week the Scottish Flood Forecasting Service (SFFS) publishes its report for 2017-2018.

We wanted all our daily Flood Guidance Statement customers, SFFS partners and supporters to know more about our operational activity and key learnings from April 2017 – September 2018, completed and planned improvements to our products and services and our future aspirations for improved flood forecasting in Scotland.

You can access the report on SEPA’s website here.

The report contains a summary of the period, with three events highlighted for further discussion. We also report on:

  • Customer feedback, which has led to improvements in our risk matrix graphics and descriptions of impacts;
  • Our Science Development Plan, which supports increased forecast lead times and th upgrade of surface water forecasting capabilities;
  • Plans for a public facing flood forecast product, to improve awareness of flood risk in Scotland.

This is intended to be the first in a series of annual reports into the activities of the service.

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World Meteorological Day 2019

Happy World Meteorological Day!

Saturday 23 March is World Meteorological Day 2019 and this year the World Meteorological Organisation has named the theme – ‘The Sun, the Earth and the Weather’. In the Scottish Flood Forecasting Service (SFFS) the weather services are provided by the Met Office, with hydrology provided by the Scottish Environment Protection Agency (SEPA), so today is a good day to highlight this partnership.

The SFFS has been going since 2011. From the start it has been a working partnership between SEPA and the Met Office. Operationally we work together to produce the daily Flood Guidance Statement, and provide forecast information to aid with the issuing of Flood Alerts and Warnings by SEPA. Additionally, the partnership is active in flood forecasting research, and facilitates the exchange of data between the organisations, as well as in training, development and public awareness of flood risk.

The railway line at Saltcoats in Ayrshire is lashed by the effects of Storm Callum in October. Flood Warnings were in force for this coast. Photo from BBC News.

Over the past year we have issued a Flood Guidance Statement every day, 54 of which have shown heightened flood risk. SEPA has also issued 215 Flood Alerts and 200 Flood Warnings in Scotland during this period, all of which required accurate meteorological input.

The work of the service, as highlighted in all the earlier articles on this site , would be impossible without the high quality meteorological data and expert advice produced continuously every day by the Met Office. For more information on recent weather and the science and history of meteorology, see the podcasts at this link.


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Using the flood risk matrix – two October events

Two widespread flood events affected Scotland in October. One affected a very large area of the West Highlands, and the other, related to Storm Callum, widely impacted England and Wales, but just clipped the south of Scotland. In both cases the flood risk matrix on the Flood Guidance Statement was put to good use to indicate the potential severity even when there was still uncertainty on where the impacts would be.

Mon 8th, Tues 9th October

There was widespread heavy rain over two days, predominantly in the West Highlands as far south as Ayrshire.

Extract from Flood Guidance Statement on Mon 8th Oct

The risk was highlighted at the end of the previous week, with FGS yellow (minor impacts likely) from Friday. Upgraded to significant impacts likely (amber) on Monday for area W of Glasgow due to rain fallen plus forecast. In the event this was downgraded the next day, but there was a widespread event with rainfall in excess of 200mm in some places. Mainly road flooding, landslides etc. The flow return period was probably <5yr in most places, though maybe locally more severe.

Flooding in Oban

This was well forecast with plenty of lead time, though there were few areas at risk and warning schemes in the area most impacted by rainfall and rivers. Amber was based on information available at the time, downgraded when forecasts came down.

Sat 13th October – “Storm Callum”

Widespread heavy rain was forecast to hit northern UK several days in advance. On Tuesday we highlighted significant impacts possible (yellow) for south of Scotland on Saturday. In the event the bulk of the rain was across the border in England and Wales. Some gauges in Scotland recorded around 60-70mm in 36 hours. There were high flows in the south of the country with minor impacts, and Hawick approaching flood warning level.

Extract from Flood Guidance Statement on Thurs 11th Oct

This was well forecast in a UK context and we were correct to highlight possibility of significant impacts, which did occur elsewhere in the UK.

In both events, the Met Office had clear sight for several days that heavy rain was coming, allowing us to give Day 5 notification of potential impacts. We were then able to adjust the likelihood, location and expected level of impacts by using different parts of the matrix as we got closer to the event.

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Medium Range Outlook for the Flood Guidance Statement

The 5 day FGS

Since its inception in 2011 the Scottish Flood Forecasting Service has provided forecasts of flood risk out to five days, by way of the Flood Guidance Statement sent to the emergency response community. Since then the scope and accuracy of medium range forecasting has increased markedly, with the result being that a reasonable view can be taken of at least the possibility of extreme weather occurring beyond the five day forecast window.

To this end, we are now able to provide an outlook for the 6 – 10 day period, on occasions where the forecasts suggest something significant, and when we feel it would provide some meaningful information to the customers. Some example of times when this might be appropriate are:

  • High spring tides, which are generally known about long in advance
  • Ex-hurricanes with long lead times, that might cause significant impacts, whether through extreme rainfall or large storm surge
  • Just prior to extended holiday periods, to aid resource allocation
  • Expected thaw following an extended cold spell and long build-up of snow
  • During a prolonged significant event to indicate when things are likely to ease up

Hurricane Ophelia – well forecast rain and surge

It’s not expected that this section of the Flood Guidance Statement will be used very often, but the ability to use it will allow us to provide useful information when available.

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Studentship opportunity – snow monitoring in Scotland

We’re supporting CEH in a summer placement for a university student who is doing a degree in a “quantitative discipline” (e.g. mathematics, statistics, computing, engineering, physics) to come and try working in environmental research.
The project is “Snow hydrology: analysing new snowpack observations to better understand hydrological model performance”. Details are in the flyer posted below – click to expand. Please pass on to anyone who may be interested.

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Review of 2017-18 EFAS Messages

As reported in the article on the 13th annual meeting of the European Flood Awareness System partners, SEPA and the forecasting service are part of this international forecasting initiative, and receive notifications when flooding is expected. As part of our input to the meeting we submitted a poster, jointly with the Flood Forecasting Centre. This entry provides a little more detail on the Scottish events covered in the poster.

It was a quiet year, with most of the activity being taken up with low level river and surface water events, or coastal event outwith the scope of EFAS. As can be seen below, only one EFAS notification was received during the year, for the north east of Scotland on 6 June 2017. What is interesting is that on the same day there was surface water flooding in parts of the Central Belt, including Edinburgh, which was not picked up by EFAS. This illustrates some strengths and weaknesses of the system, which is more geared toward large rivers – even our larger watercourses mostly fall more within the remit of the Flash Flood notification remit – than surface water flooding. Additionally the event in the south of Scotland during January 2018 was missed by EFAS, though it was forecast to some extent by SEPA’s own models – the run-off was caused at least in part by snow melt, which all models can struggle with. There were no EFAS false alarms for Scotland during this period.

Reported and missed events for 2017-18. Map graphics show EFAS Flash Flood forecast (top) and Grid-to-Grid forecast (bottom). Photos (L-R) Moray, Moray, Edinburgh on June 7


The lesson identified is that for the types of events that we see in Scotland, EFAS can be useful to help add confidence to our own forecasts, given that the source models (ECMWF weather and LISFLOOD for rivers) are independent of our own. But not everything is captured, particularly surface water events, so we should be wary of relying on it in isolation.

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