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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Challenges and innovation towards the prediction of natural hazards

The 2016 European Geosciences Union General Assembly saw us co-convene our second PICO (Presenting Interactive Content) session on operational forecasting and warning systems for natural hazards. Along with several other sessions in hydrological forecasting there were plenty of take home points regarding the challenges and innovation of natural hazard early warning.

PICO session

Delegates at the PICO session on operational forecasting and warning systems for natural hazards at the 2016 General Assembly of the EGU. 13,650 scientists from 109 countries attended the event during the six days between 17 and 22 April.

There is a growing effort in the area of real-time mapping of the consequences of hazards to support emergency response. In the Philippines, Project NOAH is responsible for the development of a storm surge advisory service with the purpose of warning for expected inundation of storm surges using hazard mapping (Santiago) – see image. A similar concept being adopted in the Chapere watershed in Bolivia involves river forecasts linked to real-time inundation scenarios to allow civil protection authorities to estimate the impact on the population (Rossi). For approaches in forecasting of surface water flooding in the UK the hazard footprint is combined with an indication of the likelihood to provide an overall indication of risk (Cole) – as seen with our approach to the Commonwealth Games pilot – which this is now being adopted on a countrywide scale in England and Wales.

Project NOAH

Project NOAH in the Philippines is a science research and development initiative to aid disaster prevention and mitigation efforts through the use of innovative information services.

A method of staged decision-making based on probabilistic forecasting was presented highlighting that a cost-loss approach was possible (Booister). The work, partly based on research in Scotland with the flood forecasting service, opens up possibilities for more flexible decision making compared to more traditional deterministic approaches.

GFN_heatmap

Real-time flood monitoring using social media.

The use of crowd sourced information to improve predictions is another area of innovation. As reported last year initiatives such as Floodtags or WeSenseIt have provided excellent examples of such approaches. This year an approach to relying on indigenous knowledge for flood and drought disaster forecasting in Ghana was presented, with the system using local co-ordination linked with satellite-based warnings (Jungermann). Coupling flood forecasting and social media was also covered in the context of the European Flood Awareness System (EFAS) and the use of the monitoring application Global Flood News (Kalas).

Challenges still remain with flash flood prediction although some innovative approaches are being trialled. On a global-scale developers of the Global Flood Awareness System (GloFAS) are setting up a system using 4-day ensemble surface runoff forecasts with a flash flood index based on climatology (Baugh). On a regional-scale high resolution convective-permitting quantitative precipitation forecasts are being used to support a new Vigicrues flash flood service in France (Dermargne).

Surface water flood forecasting

PICO presentation on real-time forecasting of surface water flooding hazard and impact

The emergence of multi hazard platforms are proving beneficial to responders with one such case in Southeastern France – RHYTMME – providing a warning and mapping system for floods, landslides and debris flows (Fouchier). Risk management strategies are now supporting multi-hazard approaches and are particularly beneficial where hazards interact both spatially and temporally (Gill) as seen with Storms Desmond (UK) and Synne (Norway) with landslide and flooding impacts being supported through national hazard assessments (Boje).

This is a unique international forum for sharing ideas on the prediction and early warning of natural hazards and we look forward to further sharing of research and operational system development at the EGU in 2017.

Posted in EGU, Flood, Forecasting, Natural Hazards | 1 Comment

SFFS at the EFAS Annual Meeting, April 2016

20160406_190755The flood forecasting service in Scotland is a partner of the European Flood Awareness System (EFAS); a EU Joint Research Centre (JRC) service which provides probabilistic flood forecast information to more than 48 member organisations across Europe based on the ECMWF deterministic and probabilistic meteorological forecasts and the LISFLOOD distributed hydrological model. Last week (6-7th April), scientists and operational forecasters from across Europe gathered in Seville for the 11th Annual EFAS Partners meeting.

The annual meeting is an opportunity for the users and developers of the EFAS models and data services to gather and exchange information on the service. Discussion included the set up and operation of the EFAS Meteorological and Hydrological Data Collection Centres in Germany (EFAS MDCC) and Seville (EFAS HDCC), respectively, and of developments to the EFAS hydrological model, including the new flash flood layers, which we received notifications from during the December and January flood events (from storm Desmond to the River Don event on the 7th January, 2016). In addition, EFAS introduced their new Rapid Risk Assessment layer which is due to become operation in the summer, 2016, and shares some similarities to the risk assessment products of the SFFS and FFC, and the introduction of a series of webinars to be delivered to partners over the course of the coming years.  Of particular interest were the presentations on the Copernicus risk mapping products and by the European Space Agency (ESA). The Copernicus datasets and products can be used to produce near real-time imagery, maps and shapefiles of flood extents during an event, and were used in England and Ireland over the December 2015 stormy period. The products could be used for other natural/man-made disasters as well. ESA were there to promote the wider use of satellite data products in flood forecasting models such as temperature and soil moisture datasets, which can be available on a range of timesteps including daily or even sub-daily in some cases. Both of these satellite products: mapping and satellite derived spatial datasets of climatological and hydrological parameters, are something which could warrant further investigation into the potential use of to improve the models and services provided by both SEPA and the SFFS.

SFFS- FFC presentation on Storm Desmond and Frank

SFFS- FFC presentation on Storm Desmond and Frank

frank_slide

Example slide from joint SFFS-FFC presentation showing the EFAS forecast and and SFFS flood guidance information & forecasts for Storm Frank

The highlight of the conference however was the presentation by myself and Rob Cowling from the England and Wales FFC- and yes I admit to being biased! We, along with Jim Casey from the Ireland Office of Public Works (who did a separate presentation), had been asked to give presentations on the recent Winter floods in the UK and Ireland in December. Due to limitations on time, and to show cross-organisation co-operation Rob and I decided to present together, enabling efficiency in delivering context to the flooding through a background introduction including of our operational models, the UK climate and hydrological regimes in general, before detailing the impacts and our forecasting performance during the Storm Desmond and Frank events. The presentation was well received with many questions asked about our forecasting systems and use of EFAS during the events.

River_auth1

The beautiful office location and Ops Room of the Guadalquivir river authority, Seville.

 

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Old friends and colleagues on the roof of Seville cathedral

In truth though, the highlight of the conference was the city of Seville itself which warrants more time for exploration that I had. The organisers of the meeting deserve congratulations on a well organised and very informative and productive meeting, but also our thanks in ensuring we had some exposure to the delights of the city. They organised a trip to the cathedral (the 3rd largest Gothic cathedral in the world) and its rooftops, before a fabulous dinner on the Wednesday night, plus a trip to the monitoring and control room of the Guadalquivir river authority who have the pleasure of working in a spectacular location (see picture). It’s fair to say we all left feeling a little envious of their office location, although they are missing the fair mountains I can see from my office window (through rain!).


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Storm Frank-Short Range Forecast Performance

Figure 1

Figure 1: Weather chart for 0000 GMT on 30th December shows storm Frank located to the NW of Scotland.

On the 30th December, 2015, new maximum peak levels were recorded on the Rivers Cree, Dee and upper Tweed due to rainfall which fell overnight from the 29th to the 30th December associated with Storm Frank; an unusually deep area of low pressure which brought weather fronts across Scotland (see figure 1). Around 370 properties were flooded in Ballater, NE Scotland, alone, but the devastation was wide spread across Scotland (see figure 2). In the previous article “Storm Frank – how was the medium range flood guidance?” we discussed the development and 2- 5 day forecast of Storm Frank and its potential impacts, whereas the aim of the current article is to discuss the variations in, and factors affecting, the forecast performance over the 24 hours prior to the event peak flows to give an overview assessment of model performance.

Figure2

Figure 2: (a)The Flood Guidance Statement (FGS) maps issued ahead of the event on the 29th-30th December, and a map (b) of public reported incidents of flooding associated with storm Frank.

Antecedent Conditions

There had been significant snowfall over the high ground of the South West and North East over the Christmas period (see figure 3a; MODIS image for the 27th December,2015). The 27th-28th December had been relatively dry but there was some rainfall overnight on the 28th into the morning of the 29th, some of which will have fallen as snow. However, by the 29th December, much of the snow cover had melted particularly at lower elevations (figure 3b). Grid-to-Grid (G2G), the gridded hydrological model which we use to forecast river flows nationally, has a snow hydrology component, which estimates snowfall, accumulation and melt based on precipitation, air temperature and basic snow pack principles, and it had simulated the observed pattern of melt.

Figure3
Figure 3: MODIS imagery (courtesy of NEODAAS/University of Dundee) for (a) 1300hrs 27th December, 2015, and (b) 1300hrs 29th December, 2015. NB- in the second image the ground extent of snow cover is obscured by cloud cover, however, the reduction in snowcover can be seen by comparing the images for the north of Scotland.

 Storm Frank- Rainfall

Figure5

Figure 4: 24 hour rainfall totals recorded during storm Frank from 0900hrs on 29th December, 2015.

The main bulk of the rainfall associated with Storm Frank occurred between 1800 hrs (+3 hours for NE Scotland) on the 29th December and 0900hrs (+3 hours for the NE) on the 30th December. Maximum recorded rainfall for the event was 130.6mm which fell in 15.5 hours at Lower Black Laggan raingauge in the southwest (Dumfries and Galloway), whereas in the Upper Dee catchment maximum rainfall was recorded at Glenmuick at 95.6mm in 15 hours. In general, 50 to 100mm of rain fell across the Southern Uplands and much of Highland Scotland (figure 4).

Sample forecast Locations

Table 1 is a sample of gauging stations located near to locations where impacts associated with flooding (see figure 2) occurred and/or new maximum recorded levels were observed (indicated by the values highlighted in red in column E). Columns F, G and H indicates the performance of the three G2G forecasts run in the 24 hours prior to the event peaks by comparing the percentage difference of the forecast peak to the observed and the difference in the estimated time of peak. For the difference in timing a negative value indicates that the forecast peak was predicted to occur earlier than it did in reality and the values are fractions of an hour (therefore a value of -0.25 indicates the forecast peak was estimated to occur 15 minutes earlier than in reality). Forecasts 1 and 2 (F1 and F2) were run at 13:45 and 18:30 on the 29/12/ 2015, and F3 at 07:30 on 30/12/2015. These forecasts use deterministic rainfall forecasts from the Met Office UKV runs at 0900hr, 1200hr and 0000hr.

Table1

Table 1: Current best estimate of observed Q and time of peak on the 30th December, 2015, recorded in WISKI at several locations across Scotland, and the performance of the three G2G forecasts at these locations prior to the event peak. Forecasts 1 and 2 (F1 and F2) were run at 13:45 and 18:30 on the 29/12/ 2015, and F3 at 07:30 on 30/12/2015. Difference of the forecast peaks and timings to the observed at given as percentage difference for flow, and fraction of an hour for time. *value for observed peak is based on the current rating and could be subject to review.

The values highlighted in yellow in columns F-H show at which forecast the previous maximum flow (column D) was forecast to be exceeded. For the 8 sites (red highlight) in table 1 where new peaks were recorded, F1 predicted the previous maximum flow being exceeded for 6 of the sites, and by F3 all of the 8 occurrences were predicted.

In general, the forecasts performed well for predicting the timing of the peak flows, and for indicating the severity of the event at least 24 hours ahead (refer to previous blog article for longer lead time identification of the severity of Storm Frank). For most sites the forecasted peak occurred ahead of the observed time (red text in table 1), which is the preferable direction of timing errors, and the forecast which performed the worst in terms of timing was forecast 2. For the upper Dee gauges which are used for assessing risk for Ballater, the estimate of time for the peaks were in the range of 3 hours too early to 15 minutes late.

Figure 6_v2

Figure 5: Forecast and observed discharge and catchment 3 hour rainfall totals for the River Dee at Polhollick. The observed precipitation is composite (gauge and radar) rainfall from G2G, the forecast precipitation are from runs at 0900hr, 1500hr and 0000hr for G2G simulations at 13:55 and 18:35 on the 29-12-15 and 07:30 on the 30-12-15.

In regards to forecast performance for the peak flows, the severity and spatial extent of the impacts were generally predicted with sufficient lead time (+24 hours) to co-ordinate emergency response. However, in terms of whether the peak flows were over- or under- estimated there is an approximate geographical split across Scotland. For the gauges located in the NE, such as those in the River Dee catchment upstream of Ballater, Forecasts 1 and 2 underestimated the peak discharge of the fluvial event, with forecast 2 performing the most poorly in terms of timings and underestimation of the peak flows (see example in figure 5). The performance of forecast 2 can in part be attributed to the underestimation of rainfall in the forecasts for these catchments, as forecast 2 generally predicted the least amount of precipitation. However, forecast 1 overpredicted rainfall for these smaller and higher elevation catchments, but the flow at the gauge locations still underestimated peak flows.

Figure7

Figure 6: Forecast and observed discharge and catchment average 3 hour rainfall totals for the River Cree at Newton Stewart. The observed precipitation is composite (gauge and radar) rainfall from UKV runs at 0900hr, 1500hr and 0000hrs for G2G simulations at 13:55 and 18:35 on the 29-15-15 and 07:30 on the 30-12-15.

Forecast 1 generally overpredicted the amount of rainfall across Scotland, but whereas forecast 2 underpredicted the rainfall for the Dee catchments, it overpredicted for the more southern gauges (and the River Dee at Park). The rainfall totals were however, still less than for forecast 1. The estimates of peak flows were generally improved over the southern catchments compared to those in the NE. Figure 6 shows the variations in predicted precipitation and river flow for the different forecasts for the River Cree at Newton Stewart in Dumfries and Galloway.

Summary

Based on the weather and national river forecasting results on the morning of the 29th December, additional simulations of G2G were run as new NWP model runs became available to the forecaster. In general the combined rainfall and river forecasts at gauge locations across Scotland indicated that this event would cause significant, and possibly severe, impacts at several locations across Scotland with sufficient lead times to enable co-ordination and planning of emergency response. For 6 of the 8 sites analysed in this blog which recorded new maximum peak river levels, the forecast run at 1345hrs on the 29th December estimated that the previous maximum recorded levels would be exceeded. However, the performance of the forecasts varies across Scotland, and is shown to be very sensitive to the rainfall forecast and model structural uncertainties particularly for the smaller catchments. It’s important to remember that the models analysed here are national scale models being used to predict local impacts and the detailing of rainfall intensity at the scale of small catchments is challenging, despite the relatively high resolution of the hydrological model (1km). The spatial variation in rainfall can be significant even in a situation of widespread (or dynamically forced) rainfall, and the highest resolution of the NWP models is 1.5km. Local rainfall totals and intensity can be focussed in certain catchments due to marginal changes in low-level airflow, with the potential of slow moving ‘mountain-waves’.

As science and technology improves, the predictions of rainfall and river flows will better represent local effects and thus the spatial variations. The evolution of such science will require careful assessment of the capability and application of such data to hydrological modelling in near real time as is required for flood forecasting. However, in the mean time, the performance of the forecasting tools and models which are available to us have been tested and proven this winter, during some of the worst events on record, to be invaluable in providing good and timely indications of the likely flood impacts.

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Storm Frank – how was the medium range flood guidance?

The rainfall associated with Storm Frank on 30 December 2015 caused some of the most severe flooding seen in Scotland for many years, particularly along the river Dee in Aberdeenshire and the rivers Cree and Nith in Dumfries and Galloway, along with record river flows and  rainfall amounts in some areas. In the first of a series of articles John Mitchell and Richard Maxey discuss how well the event was predicted, and how the forecasting service reacted in the days leading up to the flooding.

How well did we forecast the severity of Storm Frank?

In addition to the weather forecast information there was a clear signal from the Grid-to-Grid hydrological model that extreme river flows would be reached in several locations. The guidance from the Met Office discussed below helped give the hydrologists confidence in the flow forecasts that were produced.

December 25

The first signs of a major storm were noted on Christmas Day. Met Office Guidance available to the flood forecasters noted developments in the USA, where warm air was moving north from the Gulf of Mexico and cold air moving south across Canada to combine and generate a strong jet, with the potential of generating very deep lows running towards the UK later on the 29th. These developments could produce prolonged heavy rain. In addition a note was made of strong orographic modulation likely over western hills and very significant rainfall totals.

UM broadscale 300hPa gph wind speeds for 0001Z Wednesday 30 Dec Note the buckled jet extending NE’wards towards W UK, with a marked left exit (development area) lying close to NW UK at that time.

UM broadscale 300hPa gph wind speeds for 0001Z Wednesday 30 Dec
Note the buckled jet extending NE’wards towards W UK, with a marked left exit (development area) lying close to NW UK at that time.

MOGREPS Forecast Charts for 1200Z Tuesday 29 Dec Demonstrate a consistent signal for deep low pressure to be located just to the west of the British Isles. Note that whilst the signal is consistent there is greater uncertainty as to the low’s precise location.

MOGREPS Forecast Charts for 1200Z Tuesday 29 Dec
Demonstrate a consistent signal for deep low pressure to be located just to the west of the British Isles. Note that whilst the signal is consistent there is greater uncertainty as to the low’s precise location.

December 26

On Boxing Day the risk of disruptive rainfall was noted and a National Severe Weather Alert for rainfall was issued. Concern that the synoptic setup was conducive to strong orographic enhancement in addition to dynamic forcing was noted.

Boxing Day: 12Z UKPP Forecast 24-hour Precipitation accumulations for Wednesday 30th Shows locally very large forecast rainfall totals over W and SW Scotland. Note the ‘finger’ of intense totals towards the southern Grampian mountains.

Boxing Day: 12Z UKPP Forecast 24-hour Precipitation accumulations for Wednesday 30th
Shows locally very large forecast rainfall totals over W and SW Scotland. Note the ‘finger’ of intense totals towards the southern Grampian mountains.

Using the Met Office MOGREPS system forecasts noted that the majority of output suggested that some very humid air may be entrained into the system with waves developing along the cold front, allowing a broad warm sector twinned with a very strong flow to cover to the UK on Wednesday. This would provide all the ingredients required to give a further bout of prolonged, heavy precipitation across some western areas. Specifically the strongest signal for heavy rain looked to be on the Wednesday (30th), again highlighting SW Scotland in particular as potentially seeing some very significant totals. This was the first signal of a backing of the wind-flow and hence distribution of orographic rain.

The Flood Guidance Statement (FGS) issued on 26 Dec indicated a low (yellow) flood risk for the south of Scotland for 30 Dec (day 5), indicating a very low likelihood of significant impacts.

December 27

27 December: MOGREPS probability of rainfall totals >50mm (left) 24hr to 18Z Wednesday 30th December. Note emphasis for highest rainfall over Western Scotland and Dumfries and Galloway where probabilities over 60% are indicated.

27 December:
MOGREPS probability of rainfall totals >50mm (left) 24hr to 18Z Wednesday 30th December.
Note emphasis for highest rainfall over Western Scotland and Dumfries and Galloway where probabilities over 60% are indicated.

On 27th December there was reasonably high confidence in the broad development – but there was continued uncertainty as weather disturbances were expected to run along the front. Heavy and persistent rain on SSW facing up-slopes was indicated for the 29/30th December. A Weather Warning – a Yellow Alert for Rain for the 30th December was issued to the public on the 27th that indicated ‘ 60-80 mm over some higher ground within this area, and the potential for the most exposed locations to receive in excess of 120 mm.’

The Flood Guidance Statement (FGS) issued on 27 Dec indicated a medium (amber) flood risk for the south of Scotland for 30 Dec (day 4), indicating a low likelihood of severe impacts. A low (yellow) flood risk for Aberdeenshire was also idenitifed, indicating a low likelihood of significant impacts.

December 28

On 28th December guidance was still for heavy and persistent rain affecting many western areas. There was still high confidence in the spell of wet weather, though there was continuing uncertainty in detailed distribution and timing of the weather systems crossing the UK. Amber warnings of rain were issued – ‘Rainfall accumulations through this period expected to be widely 20-40mm, with 80mm over some higher ground within the area, and the potential for some exposed locations in southwest Scotland to receive 100-150 mm.’

The Flood Guidance Statement (FGS) issued on 28 Dec indicated a medium (amber) flood risk for the south of Scotland for 30 Dec (day 3), indicating a low likelihood of severe impacts. A low (yellow) flood risk for Aberdeenshire was also idenitifed, indicating a low likelihood of significant impacts.Summary Flood Guidance Statement maps for the days leading up to the event on Dec 30.

Summary Flood Guidance Statement maps for the days leading up to the event on Dec 30.

Summary

The potential for heavy, orographic rain on Dec 30 associated with Storm Frank was identified on Christmas Day. Ensemble forecast models furnished the forecasters with invaluable information to determine and communicate the likelihood of the event.
The possibility of a significant event in the south of the country was seen four days in advance (day 5 yellow) with possible severe impacts identified 3 days in advance (day 4 amber). As will be seen, the long lead time forecasts for this area were very good.

The Aberdeenshire event was flagged three days in advance (as a day 4 yellow), but as discussed above the uncertainty in the precise distribution and detailed timing of the event meant that severe impacts for this area were not identified at this early stage. Subtle alteration of wind-direction (and speed) can have marked impact on the distribution of orographic rainfall. In this case, the backing of winds to the south brought greater exposure to the south Cairngorm Mountains and Upper Deeside catchments. At the broad-scale the weather models performed well. It will always be challenging to match capability for wider-scale guidance against the demand for detailed local information.

The next article in this series will look at the forecasts for rainfall and river flow in the immediate run up to the event, how they informed the flood guidance the day before and during the event, and how they performed compared to what happened on the ground.

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RAINS: Radar Applications in Northern Scotland

Storm Frank rainfall radar (2)

Caption: 24 hour quantitative precipitation estimates from radar across Scotland for Storm Frank (29th – 30th December 2015). Typical catchment average rainfall exceeded 80 mm in 24 hours for the Upper Dee, with some point estimates of 150 mm. All background radar data © Met Office.

The past two months have brought significant rainfall across much of Scotland resulting in some severe disruption due to the impacts of flooding.  Impacts have been seen in early December with Storm Desmond, through to Storm Frank which brought major flooding along the Dee Valley in Northern Scotland.

The use of radar is essential to increase our understanding of the spatial representation and real time estimation of rainfall for flood forecasting across Scotland.  However, whilst this is a vital tool there are some unique challenges with doing so in Scotland not least the effects of the upland environment and distance from the radar.  To this end the flood forecasting service are working with the National Centre for Atmospheric Science (NCAS) and the University of Leeds to deploy a mobile X-band radar to research the use of high resolution radar measurements for improved flood forecasting.

The RAINS project (Radar Applications In Northern Scotland) will run from January to July 2016 and will be making detailed measurements of the atmosphere from a radar based in Kinloss, Morayshire, specifically looking to measure clouds and rainfall as they form across Northern Scotland.  The NCAS radar is capable of measuring clouds and precipitation in high detail and is the only one of its type in the United Kingdom.

X Band deployment

The mobile X Band radar deployed at Kinloss Barracks in Moray (left) and initial quantitative precipitation estimates on the 2nd February (right) when flooding occurred across Ross-shire.

The collaborative project involving the Met Office and Scottish Water will specifically look to improve the understanding of rainfall and the prediction of floods through comparative hydrometeorological modelling using the quantitative precipitation estimates of rainfall generated by the Kinloss radar.

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The 2005 Teviot floods: then and now

As previously reported Storm Desmond caused severe flooding over the weekend of the 5th and 6th December in parts of the country including the Teviot Valley. The River Teviot in Hawick recorded its second highest river flow on record and close to the peak levels recorded in the damaging 2005 flood. However, levels at Ormiston Mill 20km downstream recorded their highest on a record which dates back to 1960. In this article we take a look at what has changed in our capabilities in flood forecasting in the intervening ten years between these two events.

Teviot@CrailingToftsFarmNT69692522

The River Teviot in Crailing in Roxburghshire recording its highest river level on a record spanning 55 years. Copyright Ali Graham Photography.

How do the flood predictions compare?

Meteorological forecasts supporting flooding operations ahead of the 2005 flood did provide early indications with national severe weather warnings activated several days in advance. However for hydrologists what has changed is the access to more detailed spatial and temporal meteorological forecasting tools to help in the decision making process, such as the use of probabilistic rainfall forecasts based on depth and duration. What this supports is the provision of guidance in terms of what is likely, but also what could be expected as a worst case scenario.

Meteorological forecasts then and now

An example of one of the 2005 severe weather warnings for the Scottish Borders, at this time the service was based on fixed rainfall triggers (left). By comparison tools such as MOGREPS-UK that are used now provide guidance on predicted likelihood of a range of rainfall depth-duration, in this case 40mm in 6 hours, with 70% likelihood across the Southern Borders for Storm Desmond (right). Copyright Met Office.

In hydrological terms, a review following the 2005 event noted that warning lead times for this flood on the Teviot were at or around 3 hours and it recommended the development of rainfall-runoff forecasting to increase future lead times. Since then systems have been developed on a catchment scale (PDM) and national scale (Grid-to-Grid) for coupling meteorological and hydrological forecasts and as reported previously this led to flood guidance being provided several days in advance of the recent event. More crucially in the 2015 flood these predictions supported community warnings being issued some 24-hours in advance of the main flooding impacts being witnessed.

Were we more prepared for the 2015 flood?

The 2007 Scottish Government study into the flooding in Hawick, Elgin, Glasgow and other communities looked at societal impacts of these events and specifically one aspect for us how communities respond to flood warnings. At the time the study found that only 33% of those that had previously been flooded used Floodline; only 39.7% moved a car on receipt of warning; and crucially the study found that the effectiveness of a warning largely depends on the time it provides to take appropriate action. The study also noted that although local automatic voice messaging systems were in place (through Scottish Borders Council), there were issues around take up, warning messaging being reliant on two systems and speed and efficiency of warning messaging.

Rainfall for the Teviot floods

Hourly rainfall recorded across the Southern Uplands. 48 hour accumulation for the 2005 flood (111mm) and the 2015 flood (96mm). Data courtesy of SEPA.

Since 2005, SEPA has introduced a direct warning service of which over 300 individuals are now registered in Hawick, helped with the awareness of the flood risk and active community engagement through initiatives such as the Hawick Flood Group. Although the full extent of the flood is still to be assessed the response to the recent flood from Emergency Planners was that ‘we were much better prepared’ which aided the proactive evacuation of 600 people from the community. Notably whilst reports of the 2005 flood mention cars being washed away, amongst the 100 properties affected initial reports are that not one car was flooded in the 2015 event as a result of the precautionary actions.

What lessons can we take away from the 2015 floods?

Whilst the key points from the 2015 Teviot flood might be that forecasts were reasonably accurate, warnings were timely and the response was proportionate to the scale of the flood, the same might not be true about the neighbouring community of Newcastleton which was equally devastated in 2005 yet escaped major flooding this time.

Newcastleton G2G prediction for Storm Desmond

The Grid-to-Grid flow predictions for the Liddel at Newcastleton with a observed peak being recorded at 254 cumecs being closest to the minimum flow ensemble member in these forecasts.

Short range flood predictions for the Liddel Water (see figure) were similar to that of Hawick in that some levels were predicted to be close to those of 2005. However, spatial variation in the predicted and observed rainfall meant that Newcastleton narrowly missed the more severe rainfall accumulation observed across other parts of the southern uplands. This case highlights that flood forecasting continues to be challenging, however the changes over the past decade has enabled us to be more prepared for future flooding.

 

 

 

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