How suitable is quantile mapping for post-processing GCM precipitation forecasts?

Contributed by QJ Wang, University of Melbourne*

Poster session during the HEPEX Workshop at SMHI in Norrköping, Sweden.

Back in September 2015 at the highly successful HEPEX Seasonal Hydrological Forecasting Workshop at SMHI in Norrkoping, Sweden, I heard a number of presentations and saw posters on the use of quantile mapping for post-processing or downscaling GCM precipitation forecasts.

While quantile mapping was well known to be highly effective in bias correction, I was concerned that some of its limitations might not have been apparent to some people.

After discussing with Andy Wood and Maria-Helena Ramos at the workshop, I left the workshop with the idea of doing a piece of work to demonstrate both the effectiveness and limitations of the quantile mapping method.

Back in Melbourne, my colleagues at CSIRO, led by Tony Zhao and James Bennett, enthusiastically took on the research task. With inputs also from Andy and Helena, we recently published the results in Journal of Climate. The paper is simply titled: How suitable is quantile mapping for post-processing GCM precipitation forecasts? Read the abstract

In brief, quantile mapping is shown, as previously known, to be highly effective for bias correction. However, if there is still an ensemble spread reliability problem after bias correction, quantile mapping cannot fix up the problem. Think of a limiting case. The ensemble members are all identical and therefore have no spread and we know the forecast is not perfect. Applying quantile mapping will not introduce even an ounce of spread to the ensemble.

When past forecasts are not correlated with observations in any way for a particular situation, we should not be insisting on using the erroneous forecasts, and should instead revert to climatology forecasts. Take this point further with another limiting case. Past forecasts are found to be negatively correlated with observations for a particular situation. Applying quantile mapping cannot reverse or remove the negative correlation, as the order of values after quantile mapping does not change.

The good news is that there are alternatives to the quantile mapping method. In the paper, we demonstrated that the Bayesian joint probability method was effective in achieving bias correction, making forecast ensemble spread reliable, and steering the forecasts to climatology when the raw forecasts had no underlying skill.

If you are interested in the topic, take a look at the paper here. The authors would love to hear your thoughts.

Finally, may I use this opportunity to let you know that I recently made a career change by joining the University of Melbourne as a professor of hydrological forecasting. Leaving the fantastic water forecasting team in CSIRO that I built and loved was one of the most difficult decisions I had to make. I look forward to continuing to work with my colleagues at CSIRO and indeed the HEPEX community to advance research and practice of ensemble hydrological forecasting. My new email contact is quan.wang@unimelb.edu.au.

* with inputs from Tony Zhao, James Bennett, Andrew Schepen, Andy Wood, David Robertson, and Maria-Helena Ramos, after several discussions in the past months.

Posted in postprocessing, seasonal prediction | 2 Comments

Developing and running an ensemble prediction system – Interview with Jutta Thielen-del Pozo

Posted by Maria-Helena Ramos (IRSTEA)

I met Jutta Thielen-del Pozo in 2005, when I went to the JRC in Ispra, Italy, to take a post-doctoral position. I had been doing research in hydrology for some time, but I didn’t know anything about ensemble predictions when I joined her team. They were developing the European Flood Awareness System (EFAS) and the first tests using weather ensemble predictions to issue EFAS warnings were just starting. I was fortunate enough to count with Jutta’s patience and amiability to get involved in the research being done within EFAS and introduced to the HEPEX community.

This is Jutta, during the Hepex workshop in Toulouse in 2009

Jutta is now Head of the Scientific Development Unit at the European Commission since July 2016, a challenging position as the units aims at stimulating novel and trans-displinary research within the JRC through a Centre of Advanced Studies, Exploratory Research, and novel instruments such as Science and Art and Collaborative Doctoral  Partnerships between JRC and higher education institutions.

Her new position has in no way reduced her historic enthusiasm for HEPEX and its community. She acted as a HEPEX co-chair from 2007 to 2012, and much of what this initiative is today is thanks to her pushing things forward, and adding people and ideas to the group.

At the JRC, Jutta was the EFAS project leader for 10 years, from 2003-2012. She acquired a broad experience in designing and running an ensemble prediction system. Since many of us are also dealing with these issues, I have asked her some questions. Here are her answers.

MHR: In your opinion, what are the crucial choices one has to make when starting the design of an ensemble flood prediction system?

JT: First of all, I think it is crucial to understand what the system is supposed to deliver and what the expectations are. Is it a small watershed with typically flash floods where decision makers have little time to act or is it a larger river with a comparatively slower response time? Is it an urban watershed? Is the watershed entirely within one’s own administrative boundaries or are others involved? Is the decision making pathway, from information to action in case of floods, long or short? How are the vulnerability and the coping capacity of society in case of flooding?

Depending on these answers, the required lead times and acceptable accuracies of the forecasts can be determined, which, in return, will determine which input data are required and what type of models and forecasting system is most suitable. For example, for flash flood prone regions, radar data blended with nowcasting and short term forecasts will be essential, whereas for riverine flood prone areas it is rather medium-range to monthly forecasts that will be more useful.

However, I would say that although input data and process modelling are key elements for a successful ensemble flood forecasting system, equally important is a communication and training strategy, so that the results are properly communicated and understood at any point in the forecasting chain. Only then users will understand that uncertainties exist; that they are acceptable at longer lead times if at the same time they provide longer time to act; and that uncertainties can and will be reduce as the events draw nearer and more data becomes available. This is particularly true today with the plethora of data sources available, including satellite and social media.

Generally, the HEPEX community has shown that whatever type of flood, ensemble prediction systems (EPS) tend to provide longer warning times for the decision making and yield more robust results. EPS give forecasters and decision makers more time to take different preparedness actions, play through different scenarios and therefore allow both preparedness and response teams to act more decisively during the crisis.

MHR: And what are the main difficulties someone should expect when running an ensemble flood prediction system in real-time?

JT: Real time operational forecasting always puts enormous pressure on not having the process chain interrupted – and there can be manifold reasons for this. There are the technical issues on site to ensure a 24/24 business continuity (power supply, redundancy of the systems in case one or more systems fails, sufficient storage at any time of the processing chain, availability of nodes for processing…) I remember an incident of the early EFAS days when a process got into an endless loop because a simple line of code was accidently deleted, which then started filling the hard disk. That was a nightmare at the time!

Then there are software issues, e.g. in case of necessary updates not having been sufficiently tested and resulting in hiccups or termination of processes. One particular aspect of ensemble prediction systems is that it involves a lot of input and output data and, for different reasons, not all files or all ensemble members may be available.  Therefore the process chain must be able to cope with time delays, partial availability of data and files, without flawing the analysis and visualisation of files.

I think another important aspect is that, during a crisis, forecasters are often asked additional questions which then need to be answered under enormous time pressure. Therefore the system should be designed in a way that additional information and in depth analysis can be extracted at any time in an easy way without slowing down the actual forecasting capacity.

MHR: How do you see the future of HEPEX? Any topics we should focus on or new directions to consider?

JT: I think HEPEX has already taken a good direction by involving end users and different stakeholders from the beginning. Yet much of the HEPEX activity remains directed towards scientists, forecasters and civil protection. I think social media now opens up new doors to keep involving the public more directly in flood forecasting. Posting pictures while flooding is going on is an obvious way and already taking place, but possibly this could be even more integrated. There is always the prejudice that “the public don’t understand probabilities”, but perhaps it is time to put this to the test and use the outcome to the advantage of the ensemble prediction systems?

Although HEPEX is open to everybody it is not yet a full global community and mostly restricted to those scientists and end users that have the technical power to run large and complex models and data sets. Yet, flooding takes the biggest toll in those regions where such capabilities are not available. And we know that flooding disproportionally affects the poorer communities. I would therefore like to see HEPEX trying to involve also end-users and scientists from those regions where computing power is limited, and finding solutions to introduce the value of ensemble prediction there too in order to have a fairer distribution of warning information globally.

MHR: And a last question: what are your working challenges now as Head of the Scientific Development Unit at the JRC?

JT: Since my new unit targets Scientific Development in the JRC in general, it is not focused on a particular topic. Its aim is rather to become the incubator for new research not yet part of the JRC’s portfolio, to stimulate exploratory research and to use Art and Science to connect JRC scientists across the JRC and with society. Such programmes are really important – in fact, if you remember, EFAS and the ensemble prediction system benefited in 2005 from the exploratory research programme at the time.

This is exciting and challenging at the same time. In order to address the changes in sciences and changes in society, my unit fosters collaboration between natural science and technology with the social sciences and humanities. We will be involving experts at the science-policy interface. This is opening up new ways of thinking and challenges us to think across disciplines. In this sense, I hope that with my work I can continue to contribute to HEPEX and stimulate new research questions.

 Thank you, Jutta, for your time and contribution!

Posted in floods, interviews, operational systems, social participation | Leave a comment

The 15th session of the WMO’s Commission for Hydrology (CHy-15)

Contributed by Sinéad Duffy & Oliver Nicholson

The Commission for Hydrology (CHy) of the World Meteorological Organisation (WMO) recently held its fifteenth session in Rome from 7th to 13th December 2016. Oliver Nicholson and I were the Irish representatives and attended the session on Dec 8th & 9th. This was the first Irish attendance at a CHy session since 1980.

Oliver works in the Office of Public Works (OPW), the lead Irish state body for coordination and implementation of Government policy and the EU Directive for flood risk management. I work in Met Éireann, the national meteorological service of Ireland. Our two organisations are currently collaborating on the establishment of a National Flood Forecasting and Warning Service for Ireland.

Brief history of CHy

CHy held its first session in Washington DC in 1961 and since then has met every four years. Sessions have mostly been hosted in Geneva but they have also travelled to Abuja, Buenos Aires, Koblenz, Madrid, Ottawa and Warsaw.

The Commission for Hydrology has not always been known as such. The final report of the first CHy session refers to it as the ‘Commission for Hydrological Meteorology’. The reports of the following two sessions in 1964 and 1968 note the title as the ‘Commission for Hydrometeorology’. It was not until the fourth session in Geneva in 1972 that the name ‘Commission for Hydrology’ was settled upon [1].

The Women’s Leadership in Hydrology Workshop

Prior to CHy-15 session kick-off, there was a two-day Women’s Leadership in Hydrology workshop, which was attended by 30 female hydrologists from 30 countries on 5 continents. Its aim was to empower women in WMO governance structures, as currently only 20% on average of those holding governance roles in the organisation are female.

WMO’s Deputy Secretary-General, Elena Manaenkova’s concluding remarks encouraged participants to be leaders themselves and to promote the study of meteorology and hydrology to young females. She urged all attending to be role models and mentors to young female professionals.

Participants of the Women’s Leadership in Hydrology workshop (photo: WMO)

CHy15 proceedings

On day one of CHy-15 committees were established, the Commission President, Advisory Working Group Members and the Secretary-General presented reports, and sessions were held on regional activities related to the Hydrology and Water Resources Programme and decisions of Congress and the Executive Council relevant to hydrology and water resources management.

Elections were held on the morning of day two, the 8th December. Dr Harry F. Lins (USA) was re-elected as President of the Commission without opposition, and Dr Silvano Pecora (Italy) was elected as Vice-President, replacing Dr Zhiyu Liu (China).

Discussions took place on the Quality Management Framework – Hydrology (QMF-H) and what is known as Project X, a project for the assessment of the performance of flow measurement instruments and techniques. The Commission has developed a dedicated QMF-H website, and a checklist with the basic steps required to set up a credible Quality Management System to ISO level with case studies from the Canadian, Czech and New Zealand Hydrological Service.

A World Bank representative presented on hydrological services in developing countries. Hydrological information and services are vital for sustainable management of water resources and flood/drought disaster mitigation, and NHSs are important as the main source of this information but the NHSs’ roles are not widely recognised in their own countries.

Resources are inadequate and sometimes decreasing for provision of these services. Case studies of Cameroon, Madagascar, Senegal, St. Lucia, Tanzania and Uruguay are now underway to review the status of hydrological information and services systems in the developing world.

The development of WHOS, the WMO Hydrological Observing System, which is the CHy’s contribution to the WMO Integrated Global Observing System (WIGOS) was presented. It is planned that initial implementation of a fully compliant framework for WMO Executive Council approval will happen in June 2018.

Day three kicked off with presentations on the Flood Forecasting Initiative (FFI). New functionality of the Flash Flood Guidance System includes elements such as urban flash flood forecasting, multiple mesoscale model ingestion, satellite inundation mapping and surface soil moisture observations to correct the system’s soil moisture.

Actions were proposed for the FFI Advisory Group:

  • development of a list of best practices for End-to-End Early Warning System for flood forecasting;
  • development of a FFI Implementation Strategy based on projects, training programmes, guidance materials, etc. to enhance national capabilities, and to ensure that all major demonstration projects such as the Coastal Inundation Forecasting Demonstration Project and the Severe Weather Forecasting Demonstration Project include best practices for flood forecasting.

The Manual on Flood Risk Mapping was in the review phase at the time of the CHy-15 session.

The Open Panel of Commission for Hydrology Experts (OPACHE) is the reservoir of scientific and technical expertise that CHy uses to fulfil its mission activities. These activities include:

  • participating in specialized hydrologic, hydrometric, and water resources studies;
  • serving on expert advisory teams;
  • contributing to manuals, guidance material, and technical reports; and
  • participating in workshops and expert meetings.

Recognized specialists from National Hydrological Services, research institutes, water resources management agencies, and academia are eligible to become OPACHE members and any experts wishing to participate in WMO activities were asked to apply.

Italy proposed the setting up of a Global Data-Processing and Forecast System (GDPFS). This would use a Global High Resolution Model (1km grid size). The models would be developed locally, but would be available for those from other countries to see.

The UK presented a proposal to develop a pilot WMO Global Hydrological Status and Outlook System to integrate current capabilities and tools in ground-based data; satellite data such as precipitation, soil moisture, etc.; numerical weather prediction models; and hydrological models.

An open-source Dynamic Water Resources Assessment Tool was outlined in a presentation by a member of the Republic of Korea delegation. The Japanese delegation noted that they have developed a flood forecasting system called IFAS (Integrated Flood Analysis System) and AutoIFAS, which will allow local engineers to use global satellite data, together with locally measured ground observations, to simulate local hydrological processes [2]. These models are used in Pakistan and Thailand, as well as other Asian countries.

Drought management, Hydrological and climate services and Capacity Building in Hydrology and Water Resource Management also were covered on day three. Documentation and presentations for these and other areas covered in the rest of the CHy-15 session are available on the dedicated CHy-15 website.

Overall, there were representative of 52 WMO member states at CHy-15, along with lecturers, invited experts and observers from 11 international organisations and other bodies such as ECMWF, ESA, HMEI and the World Bank.

The CHy-15 session was livestreamed on the ISPRA YouTube channel and videos from the session are available online.

Group photo of the 15th session of the Commission for Hydrology (CHy) of the World Meteorological Organisation (WMO) held in Rome from 7th to 13th December 2016 (photo: A. Castellucci, Ispra – CHy/WMO)

Additional links:

[1] Askew A, ‘Hydrology and Water Resources within WMO—the Birth of a Programme’, WMO Bulletin Vol 57 (3) – 2008.

[2] Integrated Flood Analysis System of ICHARM

Posted in activities, meetings | Leave a comment

An invitation: help HEPEX program apps to teach the value of probabilistic forecasts

Contributed by Florian Pappenberger, Andy Wood, Maria-Helena Ramos, Schalk-Jan van Andel, Louise Crochemore, and Louise Arnal

This is a blog for people who usually do not read this blog. This is a blog which asks for help so that our learning and teaching games and tools become more useful and widespread. This is a blog hoping that we can find some enthusiastic volunteers.

The more people know how to use probabilistic forecasts, the better their decisions and the lower the impact caused by extreme weather or hydrology (floods, droughts etc) will be.

Weather, water and fire (and many others) forecasts are uncertain — people instinctively know this. For example, if I forecast a maximum of 15 degrees Celsius for tomorrow, you probably know it will not be exactly 15 degrees Celsius but something around that number (and you may add an uncertainty range from your experience).

Most weather and water forecast centres also understand this and produce not just a single forecast but a set of forecasts. For instance, the Global Flood Awareness System generates 51 scenarios (51 different forecasts) of what the future could look like. This enables it to issue a probabilistic forecast, which means (for the above example) that you can estimate a certain percentage chance of the temperature being above or below 15 degrees Celsius.

Despite this uncertainty, people still need to take decisions. An example of a simple decision is whether or not to take an umbrella when you leave the house. A more complex one may be whether you should stop the London Underground because of a risk of flooding along the Thames.

Probabilistic forecasts enable better decisions because you know what the uncertainties are, whereas you have no clue of them with a single forecast.

Forecast users can strengthen their understanding of the value of probabilistic forecasts, and their skills in using them, through forecasting games. There are many examples:

  • controlling a reservoir on a river to avoid droughts (here),
  • exploring the economic value of uncertain forecasts (here),
  • managing floods (here),
  • weather roulette (here) which evaluates the information in forecasts.

HEPEX has designed and implemented a number of such games (see here), but, to date, except for our first try on the online version of the “Pay for a forecast” game (here), they are paper- or presentation- based, and we would like them to reach a wider audience.

The challenge today is:

  1. Can you improve the existing ideas?
  2. Could you design a game where different players compete against each other? (*)
  3. Most importantly, can you transform the paper-based version into apps (web or phone) to reach a wider audience?

We are also interested in putting together ideas on how to set up a project (volunteer, student, commercial), which kind of partners, and how to get funding (volunteer-based, crowd-funding, H2020 and the like, commercially, etc) to enhance our tools for training and teaching the value of probabilistic forecasts.

Please contact us or any of the HEPEX co-chairs by Friday 28th April if you could contribute to engineering web-apps in support of the HEPEX initiative or of you are interested in participating to project proposals on the topic.

You can also come and meet us at the EGU poster session of the ensemble session in Vienna. Our HEPEX poster, will be displayed on Friday, 28th April, and the attendance time is from 17:30–19:00 in Hall A.


(*) In the Weather Roulette game, for instance, you would need to decide whether the app decides the odds for different outcomes. The goal of each player is to win the most in the weather roulette casino shared by everyone. Alternatively, players could each have their own casino and bet in the casinos of other players. Examples of the questions a designer would face include: On what forecasts should the odds be based? And what information is made available to the players so that they can decide how much to bet on different outcomes?

Posted in activities, projects | Leave a comment

Competition: How would you explain your work if you knew only 200 simple words?

Contributed by Louise Arnal, Rebecca Emerton, Liz Stephens, Hannah Cloke

It is not always easy to explain what you work on, especially when you have to avoid using jargon specific to your field. Yet, this is something that we almost all have to do from time to time. It is important to be able to explain your research simply in order to communicate effectively with scientists in other fields and, for example, businesses, policy makers and the public.

So we thought we’d have some fun with this and run a competition designed to really test how simply you can explain a common theme of all of our work: “Ensemble hydrological forecasting”.

Here is your challenge: using only the 200 most commonly used words of the English dictionary (listed below), you will have to explain what “Ensemble hydrological forecasting” is.

To help you out a little bit, you’re also allowed the use of the word “water”. You can make words plural and use punctuation, but you cannot conjugate verbs. You can write as much or as little as you need to explain the concept.

An ECMWF surprise prize is waiting for the winner

Submit your answer in the comment box below, starting the sentence with “Ensemble hydrological forecasting is…”.

The competition will be open until 21 March 2017, after which we will put the answers to a vote to choose a winner, who will receive a prize from the team at ECMWF.

Below is a list of words that you are allowed to use, in alphabetical order. In the first comment to this post, you will find an example if you’re struggling to get started.

Good luck!

These are the words you can use:

Posted in activities | 24 Comments

2018 HEPEX workshop, Melbourne, Australia: Breaking the barriers

Contributed by James Bennett (CSIRO) and local organizers team

In the afterglow of the highly successful 2016 HEPEX workshop in Quebec City, Canada, the planning for the next HEPEX workshop in 2018 in Melbourne, Australia is underway.

Melbourne is far way for many HEPEXers, so we thought we would give an early warning of this workshop to give you all some planning time. With this in mind, we plan to hold the workshop in February 6-8, 2018.

This is the height of summer in Melbourne, and we hope it will coax a few cold northerners to the antipodes. Melbourne is a thriving modern city, with a number of major research and operational centres interested in hydrometeorological ensemble forecasting (e.g. the Bureau of Meteorology, the University of Melbourne, Monash University and the CSIRO).

The theme for the workshop is ‘breaking the barriers’ to highlight current challenges facing ensemble forecasting researchers and practitioners and how they can (and have!) been overcome. We wish to highlight the following topics:

  • using ensemble forecasts to improve decisions in practice,
  • extending forecasts in space (including to ungauged areas) and across lead-times, from short-term to sub-seasonal to seasonal forecast horizons,
  • using ensemble forecasts to maximise economic returns from existing water infrastructure (e.g. reservoirs), even as inflows and demand for water change,
  • using ensemble forecasts to improve environmental management of rivers,
  • applying ensemble forecasts for agriculture,
  • searching for better/new sources of forecast skill,
  • balancing the use of dynamical climate and hydrological models with the need for reliable ensembles,
  • communicating forecast quality and uncertainty to end users.

More generally, we welcome contributions on new and improved ensemble hydrological prediction methods as well the application of existing methods in practical and operational settings.

As before, the Melbourne 2018 workshop will go for 3 days and include both oral and poster presentations on all aspects of hydrological ensemble prediction. We will give an update with abstract submission dates and more information – stay tuned!

Posted in announcements-events, meetings | Leave a comment

Meeting user needs for sub-seasonal streamflow forecasts in Australia

By Tongtiegang Zhao, Andrew Schepen and Q.J. Wang, members of the CSIRO Columnist Team

Good streamflow forecasts allow water management agencies to make better decisions and achieve more efficient water use. Currently, the Australian Bureau of Meteorology provides seasonal forecasts of three-month-total streamflow for over 200 gauging stations around Australia. Forecast users, particularly water management agencies, also require sub-seasonal streamflow forecasts, so that they can better plan short-term water use. Our recent study responds to this user need by testing ensemble sub-seasonal to seasonal streamflow forecasting for 23 case study catchments around Australia (Figure 1).

Zhao_1

Figure 1: Location map of the 23 case study catchments around Australia

We apply the Bayesian joint probability (BJP) modelling approach to predict monthly streamflow three months ahead. The predictors are one-month antecedent streamflow and climatic indices, including El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). In BJP, streamflow and climate variables are first normalised through data transformations. The transformed variables are then assumed to follow a multivariate normal distribution.

We evaluate the skill of sub-seasonal forecasts relative to a climatology reference. The results show that the month 1, 2 and 3 ahead forecasts are respectively positively skillful (have smaller errors than climatology forecasts) in 74%, 57% and 46% of the test cases (Figure 2). The variation of sub-seasonal forecast skill is associated with rainfall seasonality, streamflow variability and catchment geomorphology. As lead time increases, forecast skill reduces and the BJP-generated ensemble forecasts tend towards climatology. The sub-seasonal forecasts are overall reliable in ensemble spread at different lead times.

Zhao_2

Figure 2: Cumulative distributions of skill for month 1, 2 and 3 ahead forecasts

Seasonal forecasts are obtained by accumulating sub-seasonal forecasts of streamflow in months 1, 2 and 3 ahead. We find that the accumulated seasonal forecasts are reliable and more skilful than climatology forecasts. Further, the seasonal forecasts accumulated from monthly forecasts are in general similarly skillful to direct seasonal forecasts (Figure 3, below).

Zhao_3

Figure 3: Skill of accumulated and direct seasonal forecasts

The BJP modelling approach is an integral part of the Bureau’s forecasting system to generate seasonal streamflow forecasts. We have demonstrated the potential of BJP to produce reliable and skilful sub-seasonal forecasts. Our sub-seasonal forecasting work will be incorporated into the Bureau’s system to provide informative sub-seasonal forecasts for water management.

Do you want to know more about these results?

Please, check the following paper for more details: ‘Ensemble forecasting of sub-seasonal to seasonal streamflow by a Bayesian joint probability modelling approach’, Tongtiegang Zhao, Andrew Schepen, Q.J. Wang, Journal of Hydrology.541, Part B: 839-849 .doi: 10.1016/j.jhydrol.2016.07.040.

Posted in columnist, forecast techniques, seasonal prediction | Leave a comment

Flood memory and historical marks of high waters

Contributed by Maria-Helena Ramos (Irstea, France)

A flood mark in Lyon (France) for the flood event on 21 Jan 1955 in the Saone River

Last year, the Hepex Portal published a blog post by Richard Davies from floodlist.com about the UK and Ireland floods in December 2015 and January 2016. When navigating through the floodlist website, I found a page dedicated to flood and high water marks (here).

I have always found these marks indicating the level reached by the waters of a river (or any other waterbody) after a flood event to be fascinating. It is not only because of their hydrological importance or contribution to the analysis of extreme events. I like the “memorial” role they play for nature. They remind us that on those particular occasions that river was flooding or reaching levels that were remarkable for people living in the surroundings.

A recent paper (Sustainable flood memory: Remembering as resilience) has discussed the importance of keeping flood memory alive: “Flood marks, flood gauges, early warning systems (mediated by television, radio and online), public photographs, videos and news reports are the mnemonic practices that ensure that floods cannot be entirely erased from lived memory.” Interestingly, the authors mention an “unexpected materialization” of flood memory from a person that “kept a decanter on her table, which contained (after over 5 years) a volume of turbid water from when the flood had entered her property.” (check the nice photo illustrating it in the paper).

The authors’ study indicate that “Personal memory is a finite resource of potentially high-energy engagement. Forgetting how to live with flooding reveals a political economy of mismanaging memory (as much as water) that drives vulnerability.” (more about this topic can be seen here too).

The Zouave in Paris as a landmark for floods in the Seine River

Last year in France, we had severe flooding in the Seine and Loire river basins in late May-early June. A heavy rainfall event reached the northern part of France and was characterized by persistent and strong rain intensities. According to Météo-France, May 2016 was the rainiest month of May in northeast France since 1959. In some areas, rain fell over soils that were already wet due to previous rainfalls over the month, which contributed to severe flooding, mainly over the Upper and Middle Seine river basin and in several tributaries of the Middle Loire river basin.

In Paris, the increasing levels of the Seine River were followed closely during the event, due to its impact on commercial activities in the banks and the public underground transportation system. In addition, the catastrophic consequences of flooding of the Seine River also include the risk of flooding buildings such as the Orsay, Louvre and Grand Palais museums or the National Museum of Natural History. If you walk along the Seine in Paris, you will see how close these and many others monuments are to the river.

“Zouave du Pont d’Alma” in Paris on 3 Jun 2016 (source: Le Monde)

But let’s come back to the flood marks. As you probably know, the most famous “landmark” for the floods in the Seine River in Paris is the “Zouave du Pont d’Alma”. Situated at the Alma bridge (here), this statue of the artist Georges Diebolt, built in 1856, is an indicator (although not really too accurate, as  discussed in an article of Le Monde on 3 June 2016) of the severity of a flood event: in June 2016 waters went up to the hips (6.10 m), as in 1982 (6.18 m); in 1924, up to the waist (7.30 m); and in 1910, up to the shoulders (8.62 m). It is often considered that “floods are occurring in the Seine river when the statue has its feet in the water” (which starts at about 1.5 m, and can mean the beginning of trouble for many of the city’s inhabitants).

The “Zouave du Pont d’Alma” as a landmark for floods in the Seine River in Paris

The Zouave is a famous mark in Paris and I’ve just found out that it even has a dedicated song, which you can listen here or read the lyrics (in French) here (thanks to the passionate French hydrologie.org association of hydrologists and my colleague Vazken Andréassian, a collector of hydrologic poems, as mentioned here).

But how to mark a flood?

Anecdotes aside, I want to come back to the flood and high water marks. It seems it is not so simple to mark a flood as one might think. I guess (or hope) no one was really there in person doing the mark when the flood occurred. This means that a flood mark needs to be searched for just after a flood, and here comes the importance of a good technique to do it in an effective way.

The U.S. Geological Survey recently published a manual with techniques and methods to identify and preserve high-water mark data (here). They say that “searching for recent high-water marks requires an eye for detail that is best developed through field practice.” It is a well-illustrated guide and tips are included to help you collect data. These tips are  (check out page 44): Safety first; Respond quickly; Look up; Stand back; Visualize the flood; Hunt for hidden clues; Think ahead; When in doubt, collect more data.

I personally like the “Visualize the flood” tip, where you are advised to “imagine the water at the peak stage”. I think it can be a good exercise to put into practice (using our imagination) a lot of concepts we have learned about channel hydraulics, river water velocity, but also local vulnerability and flood exposure.

This is me in 2009 showing a flood mark in Paris for the 1910 flood in the Seine River

In France, we have a national database where you can add your photo and contribute to keeping the memory of floods (check here).

Do you have a similar one in your country? Would you like to tell us more about it?

Contact Hepex co-chairs and website administrators if you would like to propose a blog post telling a bit of the history of floods and flood marks in your city or country, or if you just want to post your best photo and share it with us!

Posted in data systems, floods, historical | Leave a comment

HEPEX 2016 Year in Review

Contributed by Maria-Helena Ramos, QJ Wang, Andy Wood and Fredrik Wetterhall (Hepex co-chairs)

The Hepex Portal published 46 posts in 2016. Here below the year in review, with its highlights.

A hot topic for 2016?

Certainly, the winner is: Global, continental and countrywide forecasting. It was a recurrent topic in the posts published during the year. We have learned that:

  • The current state of large-scale (global and continental) operational flood forecasting is largely due to the integration of meteorological and hydrological modelling capabilities, improvements in data, satellite observations and land-surface hydrology modelling, and increased resources and computer power (by Rebecca Emerton)
  • Large scale models of complex basins with floodplains, braided drainage network, or flat relief is an ongoing research topic in Brazil (by Ayan Fleischmann and Fernando Fan)
  • One of the challenges of international forecasting systems is that these systems have to do with inconsistent collations of data from different countries (by Chantal Donnelly)
  • A new global precipitation dataset, the MSWEP, is available and can be useful for a broad range of hydrologic applications (by Hylke Beck et al.)
  • Handling large amounts of data for ensemble forecasting can be a nightmare, and benefits are expected from using standardised, well supported and self-describing binary file formats to make data sharing easier (by James Bennett)
  • There is an active community to support the integration of GloFAS forecasts into existing national and local forecasting capabilities (by Rebecca Emerton, Liz Stephens and Hannah Cloke)
  • Solutions to improve global forecasting can arise from a joint community effort such as the one shown by the #FloodHack held on 16 -17 January at ECMWF in Reading (by Fredrik Wetterhall)

And do you know any of those brave people who accepted being interviewed for Hepex in 2016?

Check out Hepex interviews here:

A big ‘thank you’ for all the interviewees!

The ensemble of Hepex interview posts can be seen here. If you know someone who would also have something to tell us, just prepare your interview and send the post to us for online publication in our Portal.

A step into historical hydrology

A novelty in the Hepex posts this year was the theme in a post proposed by Andy Wood and colleagues tracing the origins of ESP, a widely applied technique to produce streamflow seasonal predictions.  It will be great to see more posts on related forecasting history. If you have an idea that would be of interest to Hepex readers, just write it down!

And many more activities: workshop, columnist teams, special issue, experiments, games…

  • The highest point of our community activities in 2016 was certainly the workshop in Quebec in June, with about 100 participants from all over the world. A summary post highlighted the three main aspects discussed during the workshop: science, operations and applications. It shows how Hepex is contributing to each of these aspects and, most importantly, how it is fostering the community to link them for a more integrative view of hydrological forecasting. The workshop presentations that were kindly made available can be retrieved here.
  • In 2016, we have introduced the Hepex guest columnist teams. CSIRO (Australia), SMHI (Sweden), LSH (Brazil), and Irstea (France) contributed a total of 16 posts over the year. You can see all posts here, and enjoy reading about their activities, views and opinions on hydrological forecasting and related topics.
  • Also, right in the beginning of the year, we launched the HESS special issue on sub-seasonal to seasonal hydrological forecasting. This was one of the outputs of the workshop in Norrköping/SMHI held in 2015. There are already 13 papers in this special issue, and it will remain open for submissions until 31 Mar 2017. You are welcome to propose your contribution.
  • Another output is the Seasonal streamflow forecast experiment. Data has been collected, formatted and a protocol for inter-comparisons is developed. We expect that in 2017 the first results will emerge. If you want to take part in it, check the dedicated webpage and contact the leaders of the experiment. You can also check the poster and the oral presentation we had at AGU 2016 in San Francisco.
  • Another HEPEX experiment that has been recently launched is the Data Assimilation inter-comparison experiment. It comes after the Hepex workshop in Quebec, when we had a successful “break-out session” on the topic. The DA experiment is being piloted by Dirk Schwanenberg (Kisters) and Albrecht Weerts (Deltares). Contact them if you want to participate.
  • We cannot forget that 2016 has seen the first online Hepex game: check what Louise Arnal has proposed to the community here. And if you have new ideas for new games, just go ahead and share it with us in the next year.

Most viewed post of the year?

Well, we think you can guess which one hit (again) the podium with over 600 views… if not, just check here and enjoy reading it!

So, what’s next for 2017?

  • Don’t miss the hydrological forecasting sessions at EGU on 23-28 April in Vienna: the deadline for abstract submission is 11 Jan 2017. Descriptions (and a quiz to entertain you during your holidays) can be found in this post.
  • Next year will also see the IAHS 2017 Scientific Assembly. This time the International Association of Hydrological Sciences will be holding workshops in Port Elizabeth, South Africa, from 10 to 14 July 2017. Hepex particularly encourages you to submit an abstract and participate to Session 12 – Probabilistic forecasts and land-atmosphere interactions to advance hydrological predictions. You have until 14 Feb 2017 for submissions.
  • And if you have not done it yet, submit your paper on seasonal forecasting to our special issue (see above) before 31 Mar 2017.
  • And certainly much more to come! Keep an eye on our Portal!

We invite you all to contribute with your own blog posts (tips can be found here) and to support the organization of Hepex activities in 2017.

Happy holidays!

Posted in activities | Leave a comment

Short-term optimization of a tropical hydropower reservoir operation using deterministic and ensemble forecasts

Contributed by Fernando Fan, member of the LSH Research Group Guest Columnist Team

As we said in previous posts, hydropower is the most important source of electricity in Brazil and it is subject to the natural variability of water yield. Its extremes lead to the risks of power production deficits during droughts, and to safety issues in the reservoir and downstream river reaches during flood events. One building block of the proper management of hydropower assets is the short-term forecast of reservoir inflows as input for an online, event-based optimization of its release strategy.

While deterministic forecasts and optimization schemes are the established techniques for short-term reservoir management, the use of probabilistic ensemble forecasts and stochastic optimization techniques is receiving growing attention. In a recent work (Fan et al., 2016), we showed some hindcasting and closed-loop control experiments for a multi-purpose hydropower reservoir in a tropical region in Brazil.

Fig. 1: Location of the Três Marias basin

The case study is the hydropower plant of Três Marias, located in southeast Brazil (Fig. 1). The reservoir is operated with two main objectives: (i) hydroelectricity generation and (ii) flood control downstream of the dam (at the City of Pirapora).

In the experiments, precipitation forecasts based on observed data, deterministic and probabilistic forecasts are used in a hydrological model to generate streamflow forecasts over a period of two years (Fig. 2).

Fig. 2: Data used in the 2-year period experiment

The online optimization depends on a deterministic and multi-stage stochastic version of a model with a predictive control scheme in combination with a novel scenario tree reduction technique.

Results (Figures 3 and 4) for perfect forecast show the potential benefit of the online optimization and indicate a desired forecast lead time of 30 days (blue-dots). In comparison, the use of actual forecasts with shorter lead times of up to 15 days shows the practical benefit of actual operational data (black-dot).

Fig. 3: Peak flow at Pirapora (results from the optimization using different input data and multiple lead-times for the forecasts)

Fig. 4: Volume over the 2000m³/s flooding threshold at Pirapora (results from the optimization using different input data and multiple lead-times for the forecasts)

It also appears form our results that the use of stochastic optimization combined with ensemble forecasts leads to a significantly higher level of flood protection without compromising the energy production (Figure 5).

Fig. 5: Energy generation (results from the optimization using different input data and multiple lead-times for the forecasts)

Do you want to know more about these results?

Posted in columnist, operational systems, water management | Leave a comment