Recent development of post-processing methods in short-term hydrometeorological ensemble forecasting

Contributed by Wentao Li and Qingyun Duan 

Due to various uncertainties in model inputs and outputs, initial and boundary conditions, model structures and parameters, raw forecasts from meteorological or hydrological models suffer from systematic bias and under/overdispersion errors and they need to be corrected before being used in applications. Various statistical post-processing methods have been developed to correct these errors and achieve “sharp” forecasts subject to “reliability”. As in the book “Statistical methods in the atmospheric sciences” by Wilks, statistical post-processing methods can be generally divided to two categories from the view of statistics, namely regression-based methods (e.g., ensemble MOS and logistic regression) and kernel density-based methods (e.g., BMA and ensemble dressing). An example of the flow of a regression-based statistical post-processing method is shown in Figure 1. As there is already a review of post-processing in a previous blog in 2013,  in this blog post we discuss several newly developed post-processing methods for short- to medium-term hydrometeorological forecasting.

Figure 1. An example of a regression-based statistical post-processing method for hydrometeorological ensemble forecasting, modified from Dr. John Schaake’s presentation of Ensemble Pre-Processor (EPP).

As described in several papers (e.g., Scheuerer et al., 2015), there are several difficulties in post-processing variables such as precipitation and streamflow/river stage: (1) these variables follow a mixed distribution of a positive probability at zero value and a skewed continuous distribution for non-zero amounts; (2) the heteroscedasticity problem, namely that the forecast uncertainty increases with the magnitude of forecast variables; and (3) the representation of spatio-temporal and inter-variable dependency, which is important for applications such as hydrological forecasting.

To model the hydrometeorological variables with skewed distribution and non-homogeneous variance, one common treatment is to apply transformations to normalize the variables and stabilize the variance. After the transformation, traditional statistical models under assumptions of Normal distribution and homogeneity can be applied. Examples of the transformations include the Box-Cox or power transformation in heteroscedastic censored logistic regression (HCLR) and the log-sinh transformation in Bayesian joint probability (BJP). Moreover, there are also post-processing models that directly use non-Gaussian distributions without any transformations, such as the censored, shifted Gamma (CSG) distribution-based EMOS by Scheuerer and Hamill (2015). To deal with the heteroscedasticity problem, EMOS model includes the ensemble spread of raw forecasts as predictor to adjust the non-homogenous forecast uncertainty. R packages such as “ensembleMOS” and “crch” have made it easy to apply these methods.

How to model spatio-temporal and inter-variable dependency of hydrometeorological variables has gained much attention in recent years. To solve this problem, several “shuffling techniques” have been developed, namely to “shuffle” the ensemble members generated from the post-processed probability distributions according to some “rank structures” which represent the spatio-temporal and inter-variable dependency. Among these methods, the Schaake shuffle are mostly applied, in which the ensemble members are reordered according to the “rank structures” obtained from historical observation archives. However, the drawback of Schaake shuffle is that the templates from past observations may not represent the current synoptic situation.

Recently, two types of Schaake shuffle variants have been developed. One type is the ensemble copula coupling (ECC) scheme developed by Schefzic et al. (2013). ECC reorders ensemble members according to the “rank structures” of raw ensemble forecasts, thus accounts for the multivariate rank structure information of the current synoptic situation. The other type of variants select the “rank structures” from a subset of historical observations under “similar” situations using synoptic analogs or other similarity criterions. This type of method includes the “SimSchaake” by Schefzic et al. (2016), the minimum divergence Schaake shuffle (MDSS) by Scheuerer et al. (2017) and the meteorological analogues-based Schaake shuffle by Bellier et al. (2017). Wu et al. conducted a comparison experiment of the three schemes of shuffling techniques, namely the original Schaake shuffle and its two types of variants.

Besides this progress, what challenges remain for post-processing? A 2013 blog post by Nathalie Voisin, Jan Verkade and Maria-Helena Ramos (here) included a list of challenges for post-processing, many of which still need to be worked on. We also recommend this chapter by Dr. Thomas M. Hamill, which also emphasizes several challenges in post-processing, such as developing post-processors suitable for limited training data, and sharing post-processing software and data together “to build a postprocessing community”.

What other challenges do you think exist in post-processing? We welcome your comments on your experiences and opinions of post-processing below.

You can find the full review on statistical postprocessing methods for hydrometeorological ensemble forecasting in the authors’ recently published review paper:

Li W, Duan Q, Miao C, et al (2017). A review on statistical postprocessing methods for hydrometeorological ensemble forecasting. WIREs Water, e1246.

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23 (+1) unsolved questions in hydrology

Contributed by Bettina Schaefli

Have you heard about the 23 unsolved problems” initiative of IAHS, in reference to the 23 unsolved problems of Hilbert? After the launch of this initiative in November 2017, the web-based discussion culminated in a round of brainstorming at EGU 2018 and in a voting process at the Vienna Catchment Science Symposium.

Personally, I did not contribute any question at the discussion stage. I simply could not think of a question that relates to observed phenomena, is universal and specific (the three original requirements to formulate the problems). Are all questions that I work on not related to a particular climate region or to modeling rather than observed phenomena?

The proposed questions and the brainstorming session clearly showed that most colleagues did not self-censor their ideas and simply proposed anything what hydrologists currently work on.

At this stage, I really asked myself how we could possibly bring the hundreds of questions and problems (around 260) down to a reasonable number. And what would the added value of such a process be? Asking this question around me during the brainstorming session, I got an interesting answer: at the very least, we can learn something about what our research community is concerned about.

Of course! Why did I not consider this aspect before? With renewed enthusiasm and with a complete perspective change, I went to the Vienna Catchment Science Symposium following EGU; not to decisively influence the final choice of “the unsolved problems” but to observe a scientific experiment of a new kind: put 40 scientists in a room, together with a moderator. Give them a list of 60+ questions and roughly 1.5 h to reformulate, rank or delete them. Of course the process starts slowly. People do not know each other, some hesitate to openly say what they think about questions that were obviously formulated by some of the most famous hydrologists. Should I really vote to delete the favorite question of the moderator?

The great thing about a direct-democratic process, with hand-voting, is that it creates its own dynamic. Everyone can see what you vote or that you don’t vote; and there is no time for deep thinking. Over the course of the exercise, it becomes more and more fun: the moderator announces a problem number, the audience yells “delete” or votes for gold, silver or bronze. Hands go up and down, and even the most intriguing problems are voted within a few seconds.

Incredibly enough, after three such rounds in three parallel rooms, the list was brought down to 16 gold questions and 29 silver questions. The final outcome is now in the hands of a paper drafting team and will be published in a paper with a giant author list in the Hydrological Sciences Journal. Once you read the questions/problems, you will no longer be able to decipher what complex processes have led to these specific questions. But every reader might find a few unexpected questions that trigger new thinking; and together, the selected problems nicely reflect what the hot topics are in hydrology at the moment. With some gaps however. The question of how to make hydrology more open and replicable is not reflected in the retained questions, for example.

And: the single most important problem has been completely forgotten: why is hydrology not more gender-balanced?

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Take a Breath of the Wild: geoscience in computer games

contributed by Rolf Hut

During the recent “Games for Geoscience” session at the EGU General Assembly in Vienna, researchers, many from HEPEX among them, presented how they use games to actively communicate scientific results and/or to engage with stakeholders.

The success of using games for science communication sparked a new question in us (Sam Illingworth, Chris Skinner, Casper Albers and Rolf Hut). We wonder how people in general, and earth scientists in particular, view computer-generated landscape images that are now common in (video) games. To study this, we have designed a survey in which people are asked to judge images of landscapes from both the real world and from fictional worlds. We would greatly appreciate any input for this (short) survey, which you can access here if you’d like to take part: “Into the wild: how realistic are artistic renderings?

Modern video games like Zelda: Breath of the Wild present players with a fake, but seemingly realistic, goescientific environment.

Thanks in advance!

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HEPEX Highlights from EGU 2018

Last week, 15,075 scientists from 106 countries attended the European Geosciences Union (EGU) General Assembly in Vienna. The week was jam-packed with more than 17,000 talks, posters and PICO presentations in 666 different sessions. The HEPEX community was represented across 5 oral/poster sessions and 1 PICO session, plus many other related sessions and events! Attendees could attend talks covering a huge range of research, from very local-scale all the way up to global scale studies, from flash flood forecasting to seasonal hydrological predictions, and on the history of hydrology and science communication. The week was a great showcase of the excellent work around the world related to ensemble hydrological forecasting.

The Austria Centre, Vienna

This year, we wanted to hear from the HEPEX community about their experience of #EGU18, so we sent out a “call for highlights”.

These were your highlights from the week in Vienna: Continue reading

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Using ensemble forecasts to inform risk-based operations of a reservoir in Northern California

Contributed by:  Chris Delaney, Sonoma County Water Agency; John Mendoza, Sonoma County Water Agency; Brett Whitin, California Nevada River Forecast Center; Rob Hartman, Consultant

Lake Mendocino is a reservoir located in Mendocino County, California, about 110 miles north of the City of San Francisco. This small 144 million cubic meter reservoir (Figure 1) releases water into the Russian River and provides both flood protection and water supply to downstream communities. Lake Mendocino is cooperatively managed by 2 government offices: the federal U.S. Army Corps of Engineers manages flood operations and the Sonoma County Water Agency manages water supply operations. The lake receives inflow from natural runoff as well from an adjacent river system, the Eel River, through a hydroelectric facility (Potter Valley Project) a short distance upstream of the lake. Recent changes in the operations of this hydroelectric facility have drastically reduced the average annual inflow of Lake Mendocino by 45%, contributing to a water supply crisis for the region. This crisis, among other reasons, made Lake Mendocino an ideal location to evaluate forecast based operations in an effort to recover lost water supply reliability, thus Lake Mendocino was selected as a pilot location for the Forecast Informed Reservoir Operations (FIRO) program. FIRO is led by a number of federal, state and local agencies including the U.S. Army Corps of Engineers San Francisco District (‘Corps’), Sonoma County Water Agency (SCWA), National Oceanic and Atmospheric Association (NOAA), and the Center for Western Weather and Water Extremes (CW3E) at Scripps Institute.

The primary goal of this pilot is to evaluate whether forecasts can be used to inform flood operations to improve the water supply capture of Lake Mendocino without increasing flood risk to downstream communities. So why would changing reservoir flood operations improve water supply? The primary reason relates to a currently used operational rule called the storage guide curve (Figure 2), which determines the maximum water supply storage level of the reservoir. This seasonally varying guide provides increased flood capacity in the wet months (November – February) and increased water supply capacity during the dry months (May – September).

This design works well during years with sufficient springtime (March – May) rainfall to fill the reservoir as the guide curve increases, but dry spring years can be challenging for water supply because the region typically receives very little precipitation during the summer and fall. Under FIRO, the objective is to detain wet season runoff above the guide curve level until forecasts indicate water should be evacuated to provide adequate volume for predicted flood events. Stored water released in advance of a forecasted flood event would be recovered by inflows from the flood event and held in the reservoir for water supply.

Another reason that Lake Mendocino is an ideal location for the FIRO pilot is that the NOAA California Nevada River Forecast Center (CNRFC) currently prepares hydrologic forecasts of reservoir inflows and for points downstream. A key forecast product is an ensemble forecast produced with the Hydrologic Ensemble Forecast System (HEFS), which generates a 59-member ensemble with an hourly timestep up to the 15-day forecast horizon, transitioning to a daily timestep for the 16 to 365 day forecast horizon.

A central challenge for this project is to develop new operational methodologies that incorporate forecast information to make reservoir release decisions to meet the project goals. One such methodology that is being evaluated for Lake Mendocino is called Ensemble Forecast Operations (EFO), which was developed by an engineer at the Sonoma County Water Agency, Chris Delaney (that’s me). I originally developed a simple proof-of-concept model, which I have refined with the help of my colleague and fellow engineer, John Mendoza. This methodology uses the HEFS ensemble forecast prepared by the CNRFC to evaluate the risk of reaching the maximum reservoir storage level. We want to avoid going above this maximum level because this would increase the risk of uncontrolled spillway releases and could flood downstream communities.

The way the EFO methodology works is quite straightforward. Each hydrologic ensemble member is independently modeled to forecast reservoir storage assuming no water is released. Forecasted risk is evaluated for each timestep in the forecast horizon as the percentage of ensemble member that exceed the maximum storage level (137 million cubic meters). The top panel of Figure 3 provides an example of a storage forecast with a 15-day forecast horizon and the maximum storage level shown as the black dashed line. The bottom panel of Figure 3 provides an example of the risk forecast shown as the red line. A key component of the EFO methodology is something called the risk tolerance curve, which is shown in the bottom panel as the blue dashed line. This curve defines the maximum allowable risk for each forecast timestep.

Figure 3 – (top) Storage forecast ensemble assuming zero releases; (bottom) risk of exceeding storage threshold, and operational risk tolerance level.

If forecasted risk exceeds the risk tolerance curve, as in our example, a release schedule is developed that mitigates the forecasted risk at or below the curve. For this example, the model simulated a release of 56 cubic meters per second to reduce the forecasted risk to the risk tolerance level. This is illustrated in the Figure 4 showing forecasted risk and storage levels after the release schedule has been applied. The model completes this process, updating release schedules each day as a new forecast is issued by the CNRFC.

Figure 4 – (top) Storage forecast ensemble after reservoir release schedules are calculated; (bottom) the resulting risk of exceeding the storage threshold matches the EFO risk tolerance policy.

It is important to note that a thorough analysis of the EFO methodology was made possible by a ensemble inflow hindcast dataset from the HEFS prepared by CNRFC for the Russian River Basin. The hindcast study allowed estimating what the forecast would have been for each day from 1985 to 2010, given their current forecasting skill. This allowed us to simulate reservoir operations and flows for points downstream under a variety of hydrologic conditions including the 1986 flood of record. Results show significant increases in storage levels (Figure 5) for almost the entire simulation period, with a 35% increase in median end of water year (September 30) storage levels compared to simulated existing operations.

Figure 5 – Storage levels with and without ensemble forecast operations (EFO)

Despite the generally increased storages, hindcast simulation results do not demonstrate any increased flood risk, with no instances of increased flow levels above flood stage. Figure 6 shows flows plotted as percent exceedance for the most flood prone region immediately downstream of Lake Mendocino.

Figure 6 – The distribution of downstream flows with current and EFO operations, showing that no significant increase in the risk of downstream flood-level flows with EFO.

The results of this study demonstrate that the implementation of the EFO methodology will likely achieve the goals of the FIRO Lake Mendocino pilot project – to improve water supply reliability without increasing flood risk to downstream communities. A more complete description of this study included in the Preliminary Viability Assessment Lake Mendocino Forecast Informed Reservoir Operations prepared by the FIRO Steering Committee in 2017. Following these positive outcomes, the Steering Committee is also working with the Corps to implement a revised version of the EFO methodology on an interim trial basis. For more information on FIRO and progress of the Lake Mendocino pilot project please visit the CW3E FIRO website.

We welcome comments and questions from the HEPEX community!


Additional author info: Jay Jasperse of the Sonoma County Water Agency and Marty Ralph of CW3E serve as co-chairs for the Lake Mendocino FIRO program. Rob Hartman is the former chief of the NWS California Nevada River Forecast Center, and has been a long-time contributor to HEPEX. Chris Delaney can be reached with questions and feedback at: Chris.Delaney /at/ scwa.ca.gov

Posted in case-studies, decision making, ensemble techniques, operational systems, risk management, water management | 3 Comments

EGU2018 #hepex Twitter feed – stay updated of events as they unfold

The week of April 9 sees the 2018 edition of the annual convention of the European Geosciences Union. “EGU2018” will be visited by approx 15,000 geoscientists including many working in the hydrometeorological arena. Last week, Fredrik provided us with an overview of some of the sessions and events that will be of interest to us HEPEX-ers.

Many of the convention-visiting-hydrometeorologists will carry a Twitter enabled phone which they will use to brief the world about the most salient insights gained. These 280 character gems will be displayed below.

Enjoy!

Note to Tweeps: don’t forget to include the #hepex in your Tweets!


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Hydrological forecasting at EGU 2018 – what not to miss next week!

The EGU 2018 Annual General Assembly will take place next week, from 8–13 April 2017 in Vienna as usual. The HEPEX community will be represented in many ways, and below you will find a quick guide to the most relevant sessions for hydrometeorological forecasters throughout the week. The sub-session on hydrological forecasting consists of 5 oral and poster sessions and 1 pico session. Get the EGU app now and tag the sessions!

The very first day will kick off with two very interesting sessions just after lunch, the sub-seasonal to climate, and after that the hydrometeorological forecasting session

13:30–15:00 / Room 2.15From sub-seasonal forecasting to climate projections: predicting hydrologic extremes and servicing water managers – Learn more about everything from seasonal to decadal predictions, reservoir and water resources management

15:30–17:00 / Room 2.15Ensemble hydro-meteorological forecasting and predictive uncertainty estimation – Grab a coffee and return to the same room for a very diverse session on forecasting and uncertainty estimation. Then make your way to the poster session for both sessions.

POSTER SESSION 17:30–19:00 / Hall A: Come to discuss with poster presenters for flash floods and ensemble forecasters and meet colleagues of the Hydrological forecasting sub-division.


On the second day, we dive into flash floods in the morning and the afternoon offers the very popular PICO session on operational forecasting and warning system for natural hazards:

08:30–10:00 / Room B: Flash floods and associated hydro-geomorphic processes: observation, modelling and warning – This session offers a number of highlighted talks, such as near real-time flash flood impact forecasting, validating impacts from insurance data and monitoring of ungauged catchments with photogrammetric methods

The  meeting of the Sub-Division on Hydrological Forecasting will be convened by MH Ramos, on Tue, 10 Apr, 10:30–12:00 / Room 2.83
It is open to everybody. Come and join us, notably if you want to meet colleagues or get more involved in the organization of sessions

13:30–17:00 / PICO spot A: Operational forecasting and warning systems for natural hazards: challenges and innovation – as last year, this interactive PICO session aims to bridge the gap between science and practice in operational forecasting for different water-related natural hazard

POSTER SESSION 17:30–19:00 / Hall A: The posters for the flash flood session is as always a good venue to discuss science and enjoy the hospitality


Wednesday is another packed day, with the session on droughts and water scarcity in the morning and games and statistical post-processing in the afternoon. Do not forget the HS division meeting at lunch!

08:30–12:00 / Room 2.44: Drought and water scarcity: monitoring, modelling and forecasting to improve hydro-meteorological risk management – the session includes everything from megadroughts in Chile to crop vulnerability in Kenya alongside presentations on new techniques to monitor and model droughts.

10.30-11.30 / Room L6: Towards forecasts and early warnings of natural hazards everywhere – for the Plinius Medal Lecture, Hannah Cloke will illustrate some of our recent successes, the best future opportunities and the critical challenges in forecasting and providing early warnings of natural hazards at the global scale.
The Division meeting for Hydrological Sciences (HS) will be convened by Elena Toth, on Wed, 11 Apr, 12:15–13:15 / Room B. It is the opportunity  to learn more about the way sessions related to Hydrological Sciences are organized at the EGU Assembly. You’re all welcome!

15:30–17:00 / Room 0.49: Advances in statistical post-processing for deterministic and ensemble forecasts – learn more about Bayesian post-processing techniques, post-processing of spatial extremes and proper scoring rules.

Other sessions that are of great interest:

13:30–15:00 / Room L7: Games for Geoscience – Learn how games can be a good way to promote science and practice! As you know, games has long been a part of HEPEX activities.

13:30–15:00 / Room L7: Coupled atmosphere-hydrological modeling for improved hydro-meteorological predictions – A very interesting session on coupled atmosphere-land experiments and effects of feedbacks.

POSTER SESSION  15:30 – 17:00 Hall X1  for the games and 17:30–19:00 Hall A for the droughts and Hall X4 for post-processing


Even though the hydrological forecasting sessions are already over, there are plenty of more interesting presentations to look forward to:

08:30–10:00 / Room 2.95: Advances in socio-hydrology, which attempt to better understand the dynamic interactions and feedbacks within diverse coupled human-water system

13:30–17:00 / Room C: History of hydrology – brush up on your hydrological history and learn more on hydrology in ancient Greece and India, and of course the history of HEPEX!

POSTER SESSION 17:30–19:00, will be in Hall A

Another tradition in Vienna: the HEPEX social gathering @ EGU. As in last year, it will be co-organized with partners of the IMPREX H2020 project. It will take place on Thursday evening at 8:30pm at the Restaurant Melker Stiftskeller (Schottengasse 3, A-1010 Wien). There is a limit of the number of places, so if you have not already booked, please do so via this form.


Last day of the EGU Assembly and again a full day of presentations:

08:30–17:00 / Room C: Hydrological extremes: from droughts to floods – Extreme events from floods to droughts and everything in between

13:30–17:00 / Room 0.49: Subseasonal-to-Seasonal (S2S) Prediction: meteorology and impactsa new session dedicated to understanding predictability of forecasts on the sub-seasonal to seasonal scale

POSTER SESSION 17:30–19:00, will be in Hall A for the hydrological extremes and HALL X5 for the S2S session

As you can see there is plenty to see and do in Vienna. See you there!

Posted in announcements-events, floods, forecast communication, forecast techniques, forecast users, meetings | Leave a comment

Calibrating hydrological model by river gender improves model skill

Contributed by Professor Flora Poil

Soon-to-be-published research funded by the international Hits-Sia-Ekoj research programme has shown that hydrological models can be significantly improved by using the link between river name and hydrological behaviour. Professor Poil explains:

“Anecdotally, the name of a river is often determined by its behaviour; a male river is more often turbulent, a female river more often stable. We wanted to investigate this link further.”

Genders of the main rivers in France. Source: Reddit/r/MapPorn 

All across our planet our watercourses have been assigned gender by our ancestors; from ‘Father Rhine’ to the Brahmaputra (Son of Brahma), and from La Dordogne to the Mekong (the mother of all rivers).

Following a year spent mapping river gender globally, Professor Poil’s team used river gender to determine catchment characteristics which were then used to inform setup and calibration of the HYDRO-LOOF distributed hydrological model. For a 5 year validation period they showed a 0104% improvement in skill compared to a control setup of the model.

This £142,018 ($412,018) interdisciplinary project on river gender science has strong implications for the hydrological forecasting community, as project researcher Dr Jo Key explains further:

“We believe that this research has significantly advanced the Prediction in Ungauged Basins research agenda. Using the river name as a guide, accurate models can be constructed without field visits and observations, therefore we could rapidly improve our forecasts at much reduced cost.”

Asked to comment on how this important finding relates to ensemble predictions, Professor Poil was remarkably coy:

“We all know which gender is known for being unpredictable. Let’s just say that this is something we can see in the ensemble spread. We’ve got some additional funding to look at this further, but I can’t say more at this stage”

This research will be published on the 1st of this month in the ‘Fluvial OrthOgonal Learning’ special issue of HESS.

Posted in April fools! | 3 Comments

HEPEX logo competition: reveal your inner artist!

contributed by Shaun Harrigan and Louise Arnal

We need your help! HEPEX (Hydrologic Ensemble Prediction EXperiment) needs a shiny new logo* and we think there is untapped artistic talent bursting to be free within the community, so we are running an online competition seeking the “next top logo”.

Established in 2004, the HEPEX mission is to demonstrate the added value of hydrological ensemble predictions for emergency management and water resources sectors to make decisions that have important consequences for the economy, public health and safety.

HEPEX is looking towards the next decade: better communication with the wider scientific community, practitioners and decision makers, as well as the public, has been identified as a key theme. We think this competition provides the perfect opportunity to engage the community to help us refresh the HEPEX online platform.

Competition guidelines and details

  • The logo* should reflect the essence of HEPEX
  • It will be used across all HEPEX online platforms (e.g., website, Twitter, Facebook, YouTube, LinkedIn)
  • It should be colour-blind friendly
  • Entries can be a polished vector graphics file or an image of a hand-drawn sketch (which can be made into professional logo based on the original design)
  • The word “HEPEX” doesn’t necessarily have to be written within the logo
  • Final logo copyright must be open by creative commons licence
  • Up to 3 entries per person
  • Deadline: Thursday 31 May 2018

 

Submit sketches, images, and vector graphics files by email to: blog@hepex.org

Voting, selection, and prize!

  • A vote will take place online and HEPEX-ers far and wide will be invited to vote for their favourite design (voting will close 1 week after deadline)
  • The top 3 logos with the most votes will go through for final judging by the HEPEX Chairs
  • The winner’s prize is the knowledge that their beautiful design will be the new face of HEPEX, and they will also receive a mug with their winning HEPEX logo printed (nice!)

Technical hint

If you do not have the expensive Adobe Illustrator programme, there are free and open source alternatives, e.g. GIMP image editor with many tutorials on YouTube.

What do we mean by a logo?

*A ‘logo‘: “a small graphic design that can be worked into a website banner or a letterhead; or printed on a button, sticker, a tshirt, etc.”  It doesn’t need to have a particular shape, e.g square, rectangular, circular – whatever you like!

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What are the challenges for HEPEX over the next decade?

The question sounds grand and may be a bit difficult to give a simple answer to, but that was the question put forward to the participants at the HEPEX workshop in Melbourne in February. HEPEX was founded as an initiative in 2004 with the goal of bringing the hydrological and meteorological communities to “demonstrate how to produce reliable …hydrological ensemble forecasts that can be used to assist the water resources sector to make decisions that have important consequences for the economy and for public health and safety“. The achievements in ensemble forecasting up until today have been discussed in workshops and blogs, and the success of implementing hydrological ensemble predictions is unquestionable — and HEPEX has clearly contributed. This success, however, prompts the question: has HEPEX fulfilled all of its goals, and if so should we disband the community and go our separate ways?

Top: Participants at the 2nd HEPEX workshop in Boulder, Colorado in 2005. Bottom: Participants at the 7th HEPEX workshop in Melbourne, Australia in 2018. The community is apparently growing.

What is the future of HEPEX?

The answer  to the posed questions is hopefully no — we still have a role to play. But the focus may need to shift from the technical implementation of operational systems towards the wider use and impact of hydrological ensembles. To help us answer this we took the opportunity to pick the brains of some of the sharpest researchers, forecasters and decision makers during the 2018 workshop . The goal was to gauge where the starting point of reformulating the role of HEPEX. The task was to discuss the question in small groups (4-5 people) and try to formulate 1-2 challenges for hydrometeorological ensemble predictions over the next decade. The groups were asked to formulate the challenges as specifically as possible so that they could be ideally be measurable. The groups were then asked to select a champion to pitch their idea in front of the rest of the workshop. Through the marvels of technology, the entire HEPEX assembly was then asked to rate each idea via their mobile phones, selecting from “A. Very interesting” to “E: Not interesting at all”. The votes were collated, and after translating the letters into numerical rankings from 1 to 5 (the higher the more interesting), we could quantify which ideas were received as extremely topical and important, and which received only lukewarm support.

Education, communication and dissemination

The most popular idea to emerge was “to produce a curriculum to help train the next generation of ensemble forecasters”, which reached an impressive average score of 4.6. Clearly there is a need to develop outreach and training material for the next generation scientists and forecasters and to make sure that ensemble techniques are embedded into graduate and post-graduate training. As a community we can help by developing training materials such as the Handbook and training material, but perhaps also aim to organize more training courses. Good examples include the short course in hydrological forecasting  organized last year at EGU, and the data assimilation workshop following the HEPEX Quebec City meeting in 2016.

The “Peak-box game” created by Massimiliano Zappa and Käthi Liechti. An example of training material downloadable from the HEPEX web site.

In places 2-6, all with a score above 4, were suggestions on improved communication to support better uptake of ensemble forecasts; a community toolbox of methods and techniques; a focus on risk-based decision making; user-friendly (event-based) verification measures; and better data in support of global hydrological modelling. Although the toolbox and better datasets are technical suggestions, the other three suggestions are focused on the users of our forecasts. Also just below (3.9) was a suggestion that HEPEX needs to better describe the value of ensemble forecasts. Collectively, these results implied that a lot more effort is needed at interface between developers and users.

But do not forget the data!

The other suggestions that were not as popular, but still had a score of >3, were dominated by recommendations revolving around data: big data, data assimilation for initial conditions, using new data sources and data-driven analysis. Other suggestions dealt with integrating and coupling forecasting systems, for example by running high-resolution inundation models forced by large-scale models, interating high resolution deterministic with ensemble predictions, or including local knowledge in the forecasts. Also there was also a suggestion for a forecast glossary (which supports the better communication theme).

Is HEPEX still needed?!

And so, returning to the question:  do we continue with the HEPEX mission? The answer is, thankfully, unequivocal:  YES … but we need to broaden our activities. We are already involved in a lot of work on communication, dissemination and education, but it is clear that these areas will have to be emphasized strongly in the next decade. The number of operational hydrological ensemble forecasting systems running today is impressive compared to a decade ago, and yet there is still an enormous opportunity for more systems and a lot of technical improvements (for example using new datasets and exploiting the ones we already have to improve our forecasts). However, the focus on our 6th topic in the science implementation plan, Communication and Decision Making needs to receive more attention.

The future users of hydrological ensemble forecasts need our guidance!

We welcome your thoughts!

This post was a short summary of the discussions held at the HEPEX 7th Workshop in Melbourne, Australia in February 2018.

Posted in meetings, opinion, science plan | 1 Comment