Particle Filters for Flood Forecasting  (PFFF)

Particle Filters for Flood Forecasting  (PFFF)

A collaboration between: Dr Renaud Hostache, Luxembourg Institute of Science and Technology (LIST); Professors Nancy K Nichols and Peter Jan vanLeeuwen, University of Reading; Ms Concetta di Mauro, Luxembourg Institute of Science and Technology (LIST)

The objective  of this DARE pilot project is to investigate the application of advanced filters to assimilate high-resolution flood extent information derived from SAR images (75m spatial resolution) for the purposes of improving near real-time flood forecasts.  The forecasting system is composed of a hydrological model loosely coupled to a hydraulic model with uncertain rainfall forcing (from ERA interim).  The ensemble of model outputs is compared to satellite-derived flood probability maps taking into account satellite image classification uncertainty.  Standard ensemble Kalman filter (EnKF) methods that assume a normal distribution of the observation errors cannot be applied and therefore new filters need to be developed for the assimilation.  From experiments already carried out at LIST, three challenges arise:  (i) to prevent ensemble members/particles being given a weight of zero solely due to local mismatch at a few pixels;  (ii) to reduce biases due to over-prediction of flood extent (false positive) being penalized more strongly than under-prediction; and  (iii) to reduce the risk of particle degeneration, where weights for all but a few particles go to zero. The aim of the project will be to assess how these challenges can be met using new advanced filters that are being developed at the University of Reading, such as equal-weight particle filters and variational mapping particle filters.

Flood forecasting chains have been set up to enable the evaluation of the proposed data assimilation filters in controlled environments using synthetic (twin) experiments.  Two studies have been carried out using these systems.

  1. We first use a variant of a Particle Filter (PF), namely a PF with Sequential Importance Sampling (PF-SIS), to assimilate flood extent in near real-time into a hydrological hydraulic-model cascade. To reduce the risk of particle degeneration, a “tempering” power factor is applied to the conditional probability of the observation given the model prediction (also called likelihood in a PF). This allows inflation of the model posterior distribution variance. Various values of the “tempering coefficient”, leading to different Effective Ensemble Size (EES) are evaluated. The experiment shows that the assimilation framework yields correct results in the sense that the assimilation updates the particle weights so that the updated predictions move towards the synthetic truth. It also shows that the proposed tempering factor helps in reducing degeneracy while inflating posterior distribution variance. Fig. 1 shows the synthetic truth together with the ensemble expectations (ensemble weighted means) for the open loop (no assimilation) and the assimilation (using various tempering factor values) runs.  As shown in this figure, the experiment also demonstrates that the reduction of degeneracy is at the cost of a slight degradation of the overall performance as the higher the EES, the lower the performance of the assimilation run. This is shown by the black and blue lines moving closer to the synthetic truth (compared to orange and light blue line Figure 1).
  2. We also investigated how innovative satellite earth observations of soil moisture and flood extents can help in reducing errors and uncertainties in conceptual hydro-meteorological modelling, especially in ungauged areas where potentially no, or limited, runoff records are available. A spatially distributed conceptual hydrological model was developed to allow for the prediction of soil moisture and flood extents. Using rainfall and potential evapotranspiration time series derived from the globally and freely available ERA5 database as forcing of this model, long-term simulations of soil moisture, discharge and flood extents were carried out. Time series of soil moisture and flood extent observations derived from freely available satellite image databases were then jointly assimilated into the hydrological model in order to retrieve optimal parameter sets. The performance of the calibrated model was evaluated using the tempered PF in twin experiments. This synthetic experiment shows that the assimilation of long time series (~10 years) of observations of flood extents and soil moisture maps acquired every three days enable a satisfactory calibration of the hydrological model. The Nash Sutcliffe Efficiency, computed based on the comparison of simulated and synthetic discharge time series, reach high values (above 0.95) both during the calibration period and a 10-year validation period.

Figure 1: Water surface elevation time series at Saxons Lode: synthetic truth (red), open-loop (green) and assimilation experiments using the standard PF-SIS (black), and using various tempering factor values (blue, light blue and orange) enabling various effective ensemble sizes to be reached (indicated between parentheses as percentage of the ensemble size). The vertical dashed lines indicate the assimilation time steps. PF-SIS=Particle Filter with Sequential Importance Sampling. EES=Effective Ensemble Size.


A Toolkit for Community-Based Flood Monitoring

A Toolkit for Community-Based Flood Monitoring

by Elizabeth Lewis, Geoff Parkin Tessa Gough, Newcastle University

This DARE pilot  project addresses the Digital Technology/Living with Environmental Change Interface by supporting communities at risk of flooding to utilise emerging technology to play an active role in collecting and sharing data to aid flood response and to sensitize communities to climatic changes by providing an enhanced understanding of their environment.

The project is engaging with potential citizen scientists to use Private Automated Weather Stations (PAWS) to gather rain data and share those data to online platforms where they can be accessed by the public, forecasters, flood managers and researchers. Engagement activities are being run promote citizen science participation and to better understand the motivations and barriers to rain data collection.

Workshops have been hosted in Newcastle museums over the school holidays to share information on the risks of flash flooding, natural flood attenuation, checking rain data online, operating a weather station and interpreting rain gauge data. Games illustrating the key concepts were available; along with posters, demonstrations and discussion with participating climate scientists from Newcastle University. Over 800 people interacted with the games and demonstrations over 4 days. The cost of weather stations was cited as a reason for not collecting rain data, along with not knowing it was possible. The workshops raised awareness among people who had not previously considered participating. Participants were directed to a website (  and support email address that we have developed for this project to support citizen scientists with any issues around installing a weather station and contributing their data to the Met Office Weather Observations Website (

A presentation was given to 42 teachers in the North East to encourage schools to get involved with the project. A workshop will be held with 25 children age 9 – 13 years old at a local school to look in detail at how weather stations work, and, the impacts of wild weather globally and locally. Further workshops with the schools are planned.

Images in order from left to right: Promotional Poster; Elizabeth Lewis at a workshop in a museum in Newcastle; A game at the workshops

Merging SAR-derived flood footprints with flood hazard maps for improved urban flood mapping

Merging SAR-derived flood footprints with flood hazard maps for improved urban flood mapping

Contributors: David Mason (University of Reading), John Bevington (JBA), Sarah Dance (University of Reading), Beatriz Revilla-Romero (JBA), Richard Smith (JBA), Sanita Vetra-Carvalho (University of Reading), Hannah Cloke (University of Reading).

This DARE pilot project is investigating a method of improving the accuracy of rapid post-event flood mapping in urban areas by merging pre-computed flood return period (FRP) maps with satellite synthetic aperture radar (SAR)-derived flood inundation maps. SAR sensors have the potential to detect flooding through cloud during both day- and night-time. The inputs are JBA’s Flood Foresight dynamic flood inundation extent and depth maps (updated every 3 hours), and a high resolution SAR image sequence. The SAR returns are used only in rural areas, including those adjacent to the urban areas, so that there is no need to take radar shadow and layover caused by buildings in urban areas into account. Also, rural SAR water level observations should be able to correct errors in model water elevations, because the JBA model thinks that all flooding is fluvial. On the other hand, it is an advantage to use the model’s FRP maps in urban areas, because these know where urban areas that are low are protected from flooding.

The project developed a method for detecting flooding in urban areas by merging near real-time SAR flood extents with model-derived FRP maps. The SAR flood detection is based on the fact that water generally appears dark in a SAR image. Urban areas that are protected (e.g. by embankments) have high return periods in the FRP maps, and their effective heights are correspondingly increased. The SAR water levels found in the rural areas are interpolated over the urban areas to take into account the fall-off of levels down the reach. The model waterline heights are similarly interpolated. The interpolated height maps from SAR and model are combined to a single map, which is used to estimate whether an urban pixel is flooded. The method was tested on urban flooding in West London in February 2014 (see image 3) and Tewkesbury in July 2007. It was compared to a previously-developed method that used SAR returns in both the rural and urban areas. The present method using SAR returns solely in rural areas gave an average flood detection accuracy of 94% and a false positive rate of 9% in the urban areas, and was more accurate than the previous method. A journal paper is in preparation.


Images: Urban flooding in West London in February 2014

Controlling and mitigating urban flooding with DA

Controlling and mitigating urban flooding with DA

by Prof Onno Bokhove and Tom Kent, PDRA,  University of Leeds
(The University of Leeds is a collaborator on the DARE project).

Motivated by the Boxing Day 2015 floods in Yorkshire (involving the Aire and Calder Rivers), we aim (i) to explore strategies of dynamic flood control and mitigation, and (ii) to assess and communicate flood-mitigation schemes in a concise and straightforward manner in order to assist decision-making for policy makers and inform the general public. To achieve our objectives, we are developing idealised observing system simulation experiments (OSSEs) using novel numerical models based on the Wetropolis flood demonstrator. Wetropolis is a physical model that provides a scientific testing environment for flood modelling, control and mitigation, and data assimilation, and has inspired numerous discussions with flood practitioners, policy makers and the public. Such discussions led us to revisit and refine a procedure that offers both a complementary diagnostic for classifying flood events (from gauge data and/or simulations) and a protocol to optimise the assessment of mitigation schemes via comprehensible cost-effectiveness analyses.

We have developed a protocol that revisits the concept of flood-excess volume (FEV). It is often difficult to grasp how much water is responsible for the damage caused by an extreme flood event, and how much of this floodwater can be mitigated by certain mitigation measures. Our protocol not only quantifies the magnitude of a flood but also establishes the cost-effectiveness of a suite of ‘grey’ engineering-based measures and ‘green’ nature-based solutions. Using river-level gauge data and mitigation schemes from the UK and French rivers, we demonstrate objectively the effectiveness of measures that can help stakeholders make decisions based on both technical and environmental criteria. The protocol should form a preliminary analysis, to be conducted prior to more detailed hydraulic modelling studies. In collaboration with colleagues from Univ. Grenoble, our work has been published in an international journal and further disseminated at numerous meetings and conferences. To date, it has contributed to the EU-funded NAIAD project through our colleagues in France and we are exploring future impact studies internationally. In our recently submitted article, a basic numerical model of Wetropolis is used to determine the relevant time and length scales prior to its construction as a physical model. We are developing the hydrodynamic modelling further, both mathematically and numerically, in order to conduct idealised experiments in flood control and mitigation.

Image  ‘FEV concept’


  • Bokhove, O., Kelmanson, M. A., Kent, T., Piton, G., & Tacnet, J. M.: Using flood-excess volume to assess and communicate flood-mitigation schemes. EGU general assembly, Vienna, April 2019 (oral). Available online.
  • Bokhove, O., Kent, T., de Poot, H., & Zweers, W.: Wetropolis: models for education and water-management of floods and droughts. EGU general assembly, Vienna, April 2019 (poster). Available online.
  • Kent, T., Cantarello, L., Inverarity, G., Tobias, S.M., Bokhove, O. (2019): Idealized forecast-assimilation experiments and their relevance for convective-scale Numerical Weather Prediction. EGU general assembly, Vienna, April 2019 (oral). Available online.
  • Bokhove, O., Kelmanson, M. A., Kent, T., Piton, G., & Tacnet, J. M.: Public empowerment in flood mitigation, Flood & Coast conference, Telford, June 2019 (oral).
  • Bokhove participated in the ‘Landscape decisions’ program at the Isaac Newton Institute, Cambridge (July/August 2019). Web:

SeriousGeoGames – Inundation Street- Flood Warning Video

by Chris Skinner – Research Fellow, Energy and Environment Institute, University of Hull & BetaJester Ltd

Inundation Street is a pilot project funded by DARE. It will create an immersive 360 video experience highlighting the impact of flooding on households. The video will demonstrate some simple steps that can be taken to reduce these impacts. The YouTube video will be available for free and will be exhibited using virtual reality headsets at events.

The development of the application is in progress. A timeline and script has been finalised. A voiceover has been recorded.  A demo of the application was shown at the Flood and Coast conference, with interest expressed by the Environment Agency. Discussions are in place with Hull City Council and the Living with Water partnership about using the application.




Ellicott City security cameras could offer useful and real time flood information

Ellicott City security cameras could offer useful and real time flood information

by Sanita Vetra-Carvalho

We have come across an illustrating source of a network of security cameras capturing a flash flood in Ellicott City, Maryland, US on Sunday 27th of May 2018. The video is a collage of 12 cameras all located on or near the Main Street in Ellicott City. The information from these videos would have been useful at the time of the flooding.

The videos clearly show how the Patapsco River and two out of its four tributaries (Tiber River and Hudson River) rapidly swell and overflow. We see how this results in the Main Street also becoming a fast flowing river with water washing away cars, destroying buildings, and accumulating debris. The flood lasted only four hours but caused catastrophic damage to local infrastructure, residents property, and claimed a life of a National Guardsman [1,4].

Figure 1. The map showing Ellicott City, Maryland and adjacent rivers. Image credit USA Today.


The cameras were installed by a local property owner, Ron Peters and can be seen in this YouTube video:


The flooding event

A storm released nearly two months of rain, over 9 inches (24cm) in just two hours (3 to 5pm local time), which swept away several roads, cars and brought more than 10 feet (3.0 m) of rapidly moving water down Main Street in the Old Ellicott City [1]. The old city is a very urban area set in a valley next to Patapsco River and its four tributaries. Due to the urban landscape the rainfall has nowhere to go except for running down the valley to the main river.

This was the second 1-in-1000 flood event within two years in Ellicott City. Both 2016 and 2018 events claimed lives and caused millions of dollars in damage [1,4]. However, flooding is nothing new to this city.  The city officials are looking into introducing green areas in the city to allow the rain water to be absorbed into the ground reducing the surface runoff.


New flood alert system

Associate Professor Nirmalya Roy and his group from University of Maryland Baltimore County (UMBC) are working on using a network of temperature and liquid sensors and have produced a new flood warning system for Ellicott City [2,4]. They are also working on using the local flood related information from social media such as Twitter into the flood alter algorithm which warns public through loudspeakers in the city [3,4].

It is clear that the videos captured from these security cameras provide a rich source of water information of the rivers and the Main Street. Information such as water levels and surface velocities can be extracted from these videos [5] and used as part of an existing flood warning system or an independent one. Further, videos also capture additional information on floods and damage caused that is valuable to rescue teams, insurance companies etc.


Flood Inundation Mapping with Data Assimilation or Summary of Zhiqi Hu MSc thesis

Flood Inundation Mapping with Data Assimilation or Summary of Zhiqi Hu MSc thesis

Due to climate change flooding is predicted to increase in frequency and intensity across the globe and it is imperative we can produce accurate and timely flood forecasts for decision-makers before and during floods.

Zhiqi Hu, an MSc in Atmospheric Ocean & Climate student at University of Reading, worked with us and JBA Consulting during her masters project investigating if a probabilistic ensemble weighting method can improve  Flood Foresight ensemble flood map forecasts using satellite observations during the flood event in India, Brahmaputra river basin in August 2017. Her work is summarised in this poster.


Flooding from Intense Rainfall

Flooding from Intense Rainfall

Several members of the DARE team were involved in the  NERC Flooding from Intense Rainfall (FFIR) programme open event, held at the Royal Society in London on 27 November 2018.

Dr Linda Speight, FFIR Policy and Impact officer wrote this overview of the event.

Over 3 million households are at risk of surface water flooding in the UK and this number is set to rise in the future. Surface water flood events happen quickly and affect small areas, the surrounding region may not see any rainfall at all. This makes them difficult to forecast.

Through the NERC funded Flooding from Intense Rainfall programme (FFIR), meteorologists, hydrologists, scientists, consultants and operational experts are working together to reduce the risks of damage and loss of life caused by surface water and flash floods.

The research includes everything from historic newspaper archives to drones and high speed computers. It has identified places vulnerable to flash flooding, developed new techniques for monitoring rivers during flood events, improved weather forecasts for intense rainfall and demonstrated the potential for real time simulation of floods in urban areas. Importantly the five year programme has helped improve communication between people in the hydrology and meteorological research communities. This will have lasting benefits into the future.

At the programme showcase event at the Royal Society in November 2018 there was a hands on opportunity to interact with the challenges of flooding from intense rainfall. Alongside presentations and an expert panel debate, participants could immerse themselves in a virtual reality simulation of a flash flood, watch convective rainfall develop on a giant forecast globe and share their thoughts on the modelling and communication chains that underpin flood forecasting.

A short video about the programme is available here


Or you can find out more details at

Dr Sam Illingworth from Manchester Metropolitan University responded to the event with poetry:


After the Flood


When I thought of floods

I thought of the heavens breaking forth

In biblical proportions.

Forty days and forty nights of rain.

I thought of Boxing Day 2015;

The pain in my left hand as I scooped

Dirty water out of my in-law’s outhouse

Using nothing

More than a gravy boat and lashings

Of dampened Christmas spirit.


When I thought of floods

I thought about days of sustained rainfall.

It never even crossed my mind that Surface water flooding

Or thunderstorms could decimate the land

In hours;

Not days.


When I thought of floods

I thought about rain gauges and sandbags;

I didn’t think about how convective events form,

How soil moisture could be used to forecast flow,

Or how our future of flood defence

Could ever be bound to our arid past.

To my great shame I did not even consider:

The conditioning of least-squares problems in variational data assimilation.


When I thought of floods

I thought of observations;

Of closing the floodgates after the horse had bolted.

Observations that masked an inevitable inability

To adapt to our environments.

I thought of shattered communities,

Broken apart not just by the unrelenting force of the rising waters

But by the isolation and helplessness of being

Told to sit and wait in silence

For the cavalry to arrive.


But now….

Now when I think of floods

I think of our improved knowledge of catchment susceptibility,

And how this will help decision makers

Identify locations at risk of flooding.

I think of being able to forecast a flood event in real time,

And how this will enable better decision making and communication.


But most of all I think about people.

Of end-to-end-forecasting, knowledge sharing, and upstream engagement.

I think about how flood chronologies can

Provide a powerful data set

To develop storylines around flood histories;

Histories which can be used to engage local communities.

And how these communities can not only learn

To be resilient,

But can help to build the resilience

That we need;

To stop us all

From being washed away.



DARE first field trip to Tewkesbury

DARE first field trip to Tewkesbury

The Dare team went on a field trip last month! It was a well planned and executed trip – as you would expect from a group of mathematicians. It was also a very interesting trip for us since most of us have only ever used data (e.g. for improving forecasts) not collected it. Even better Tewkesbury area has become a sort of benchmark for testing new data assimilation methods, ideas, tools, observations, etc, and so many of us have worked with LisFlood numerical model (developed by a team led by Prof. Paul Bates at the University of Bristol) over the Tewkesbury domain. We have seen the river runs in the model outputs, watched the rivers Avon and Severn go out of banks in our plots, and investigated various SAR images of the area but we have never been to the area. We generally do not need to visit the area when working with the models, however, now that there was a chance to do so, it was no surprise that many of us were keen to go. And we did go like ‘d’ A-team:

Figure 1. ‘d’A-team have arrived!


However we had a more important reason for visiting too – we were going to the Tewkesbury area to collect metadata from a number of river cameras located near Tewkesbury town. These river cameras are high definition webcams owned and serviced by Farson Digital Ltd in various location over the UK. We had recently discovered that six of such cameras are within the LisFlood model domain and have captured the November 2012 floods in the area. With the permission from the Farson Digital Ltd, we have obtained hourly daylight images of the floods from 21st November 2012 to 5th of December 2012. Hence, the aim our trip was to obtain accurate (with errors of no more than few centimeters) positional information (i.e. latitude, longitude, height) of the cameras themselves as well as the positional information of a number of markers in the images for each of the cameras. We need this information to extract as accurately as possible water extents and water depth from these images using image processing tools (which we are currently working on).

Figure 2. Rivers Avon and Severn domain map in the LisFlood model with the six river cameras located where the red/white circles are positioned.


To take these measurements we had borrowed some tools from the Department of Geography at the University of Reading. We used a differential GPS tool (GNSS) to very accurately (on order of few centimeters) measured the position of a given point in 3D space, that is its latitude, longitude, and height above the sea level, however, it had to be used on the ground (e.g. could not measure remote or high points such as building corners where some cameras were mounted) and not be too close to buildings or large trees. To measure remote and high points we used Total Station, which allowed us to shoot a laser beam to the desired point to measure its 3D position in space.

Figure 3. Steve Edgar from the Environmental Agency showing masterclass with TotalStation.


We had planned to visit all six cameras within the space of the two days 16th and17th of April, however, despite our best plans and fantastic organisation skills we were too ambitious with our time and we had to drop the camera furthest from our base – the Bewdley camera (see map with camera positions in figure 2). Thus, on our first day, we took measurements from Wyre Piddle, Evesham, and Digglis Lock cameras, spotting ourselves live on the Farson Digital Ltd site.

Figure 4. Dare team spotted at the Evesham site live on Farson Digital Ltd river cameras on 16th of April.


We returned to our base – the Tewkesbury Park Hotel, to be joined by the Ensemble team from the Lancaster University. Ensemble Project is lead by Prof. Gordon Blair, and as Dare is funded by the EPSRC Senior Fellowship in Digital Technology for Living with Environmental Change. It was very interesting to meet the Ensemble project team and learn more in-depth about their work, future interests, and scope for the collaboration.

Figure 5. Prof. Gordon Blair (University of Lancaster) giving an overview of the Ensemble project and introducing his team.


On our second day, the Dare team visited the Tewkesbury camera while the Ensemble team learned more about the purpouse of the data collection and the Novermber 2012 floods in the area. Then we all jointly measured a large number of points at the Strensham Lock. In 2012 we all would have been totally sumberged in water in this picture since the flood waters completely swallowed the island on which the house is standing flooding the building along with it.

Figure 6. Dare and Ensemble project teams at the Strensham Lock.


Our grand finale was the meeting with the director of the Farson Digital Ltd Glyn Howells as well as a number of stakeholders who have commissioned the cameras we visited. It was very interesting for us to learn how the network of the river cameras was born from the need to know and understand the current state of the river for a variety of river users – fishermen, campers, boaters, etc. Also, how these cameras have become invaluable assets to many stakeholders for various reasons – greatly reducing the number of river condition related phone enquiries, monitoring river bank and bridge conditions, and so on.

Now a month later we have downloaded and processed the data we collected from these stations. In figure 7 we have plotted the data points we took at the Tewkesbury site, owned both by the Environmental Agency and Tewkesbury Marina (both of which we greatly thank for their support and assistance before and during our trip, especially to Steve Edgar from EA and Simon Amos and Bruno from Tewkesbury Marina). In the figure, the red dots are the camera positions – pre-2016 and current camera positions, and the black dots are all the other measurements we took using both the TotalStation and GNSS tools, which are plotted against the Environmental Agency lidar data with 1m horizontal resolution.

Figure 7. Locations of the point measurements from both Total Station and GNSS we took at the Tewkesbury town. Red dots are camera locations (pre-2016 and current positions), black dots are measurements of various reference points that can be seen from the camera. To make this image we used the Environmental Agency 1m horizontal resolution lidar data and LandSerf open source GIS software.


We are currently working on extracting the water extent from these images which we then will use to produce water depth observations. Our final aim is to see how much forecast improvement such rich source of observations offer, in particular, before the rising limb of the flood.

We are very thankful to Glyn Howells and the various stakeholders for permitting us to use of the images, allowing us to take the necessary measurements, assisting us on the sites, and joining at the workshop!

Our first DARE workshop

Our first DARE workshop

by Sarah Dance

Workshop participants

The DARE team organised a workshop on data science for high impact weather and flood prediction, held by the river at the lovely University of Reading Greenlands Campus in Henley-on-Thames, 20-22 Nov 2017. The workshop objectives were to enable discussion and exchange of expertise at the boundary between digital technology, data science and environmental hazard modelling, including

  • Data assimilation and data science for flood forecasting and risk planning
  • Data assimilation and data science for high impact weather forecasting
  • Smart decision making using environmental data

The meeting was attended by over 30 participants from  5 different countries. We had some great presentations ( to be made available on this webpage) and discussion. We came up with some recommendations to help promote and deliver research and business applications in the digital technology-environmental hazard area. We plan to write a meeting report detailing these recommendations that we hope will be published in a peer-reviewed international journal.  Watch this space!