Research “Hylight”: Complex Picture for Likelihood of ENSO-Driven Flood Hazard by Emerton et al.

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Rebecca Emerton

In March, Rebecca Emerton and colleagues published a paper on ENSO-Driven Flood Hazard in Nature Communications. The paper found a more complex picture than is often assumed. We decided to ask Rebecca a few questions about the paper.

Q: Where are you from, where are you based, and what are your current research interests?

A: I grew up in England, not far from Reading – where I studied for my Masters in Meteorology for 3 out of 4 years (the other year being spent at the University of Oklahoma, USA) – and where I’ve returned to work on my PhD through the SCENARIO doctoral training partnership. I’m now based in the University of Reading’s Geography and Environmental Science department, and I also work closely with the Meteorology department and the European Centre for Medium-Range Weather Forecasts (ECMWF). My current area of research looks at finding ways to provide earlier warnings and indications of floods across the globe, through large-scale climate patterns or seasonal forecasts, for example.

Q: What is the take home message of your paper?

A: So I should start by saying that the idea for this research came from the fact that often, people use information on the impact of El Niño and La Niña on rainfall around the world, as a proxy for where might experience flooding (or drought). We wanted to produce similar information based on the hydrology, to give an indication of where might be more or less likely to flood during an El Niño or La Niña that is based on river flow rather than rainfall. Our results showed that actually, this is much more complicated than is often perceived, and in fact using rainfall as a proxy for flooding may well cause you to under- or over-estimate the likelihood of flooding. So I suppose the take-home message is that while probabilities of increased or decreased flood hazard, like the ones we map in the paper, can provide some useful information, they are actually much lower and more uncertain than might be useful for decision-making across much of the world, and these uncertainties need to be communicated more widely.

Q: You are currently doing your PhD in collaboration with an operational weather centre (ECMWF), has your experience here influenced your research paper?

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Rebecca’s Paper

I would say that collaborating with ECMWF has influenced my PhD studies in many ways, including this paper. I was able to work with the scientists at ECMWF who were producing the 20th-century global river flow dataset that we used for this research, and the team there were a great help when I was learning how to use and process this – just one variable contains over 10 billion values and it was a new challenge for me to work with such large datasets! The combination of working in both an academic and an operational environment gives me different perspectives on the work I’m doing, and has given me the chance to talk to users and decision-makers as well as researchers, to get a feel for how information on ENSO impacts was being used and understood and how my research fit in with that.

Q: In the paper you use a newly developed global river flow reconstruction dataset for the twentieth century (ERA-20CM-R). Do you see wider uses for such a dataset within hydrology?

A: Absolutely – model reconstructions such as this one can be invaluable, particularly when considering larger scales and areas where little or no data is available. Of course, modelled data has its limitations and uncertainties, particularly when going back to the early 1900s, but I believe there are opportunities here for work related to ungauged basins, large-scale hydrology, and looking at long-term hydrological data. One great thing about ERA-20CM-R is that it contains 10 ensemble members, which allow some evaluation of the uncertainty in the data itself.

Q: Do your research findings have practical implications for flood risk management and society?

A: I would say so – we provide the hydrological counterpart to the information available on the meteorological impacts of ENSO, through maps of the probability of increased or decreased flood hazard throughout El Niño and La Niña events. We somewhat call into question whether the information currently being used (I’m thinking mainly of the oft-seen maps of the world with large areas circled as ‘wet’ or ‘dry’, ‘warm’ or ‘cold’) is the most useful in terms of early warning and disaster risk management during these events – and emphasise that it’s important to take into account the hydrology too! This sort of information can be used in conjunction with what’s already out there, and more local scale research on ENSO impacts, to provide a more complete picture of the likely impacts of El Niño and La Niña, particularly for those needing to make decisions based on the potential risk – such as governments and humanitarian aid organisations.

[END] – Interviewed by Shaun Harrigan & Wouter Berghuijs

This interview is part of the new YHS Research “Hylights” series to showcase interesting and outstanding work by early career scientists. Selection criteria are not set in stone, but reasons to select work can include e.g. novelty and relevance of findings, fun of reading, unique collaborations, media coverage and generated controversy. Selected work will be provided with a short layman summary, and a short written or video interview with the (first) author(s). Tips can be sent to younghydrologicsociety@gmail.com or t.h.m.vanemmerik@tudelft.nl.

Reference paper: Emerton, R., Cloke, H. L., Stephens, E. M., Zsoter, E., Woolnough, S. J. and Pappenberger, F. (2017), Complex picture for likelihood of ENSO-driven flood hazard, Nature Communications, 8, 14796, doi:10.1038/ncomms14796.

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