Dr Adam Griffin, a hydrological statistician and the Flood Estimation team leader at UKCEH, reflects on a milestone year for a milestone project…
UKCEH and its predecessors have over the last 50 years led the way in developing statistical flood and rainfall frequency estimation methods for use in policy, industry and research across the UK, and which have been directly referenced in the development of similar methods across the globe. Through reports, procedures, software and datasets, thousands of users/experts and millions of people are directly or indirectly impacted by decisions based on these methods.
So I wanted to reflect on what kick-started a lot of this work: the Flood Studies Report of 1975.
A seminal work
The Flood Studies Report (FSR) was published in 1975 as a seminal piece of work involving more than 25 people from the Natural Environment Research Council (NERC), Institute of Hydrology (a forming part of UKCEH), the Meteorological Office (now Met Office), and the Hydraulics Research Station (now HR Wallingford), with help from the Irish Office of Public Works. It’s been great to see the progression of these major institutions over time.
The FSR consists of five volumes:
Volume I: Hydrological Studies. A precursor to the current Flood Estimation Handbook (FEH) statistical procedures, this included the first national-scale methods for statistical flood frequency. It also included a key development of the design flood hydrograph, which modelled the whole rainfall and river flow of a storm and associated flood, rather than just estimating its peak flow. Although the Statistical Flood Frequency method and the Design Flood method have moved on, I can see where our current work is so strongly built on these foundations.
Volume II: Meteorological Studies. Led by the Meteorological Office, this research looked into the regional analysis of rainfall extremes, including mapping the 5-year rainfall depth across different durations across the UK. It forms the foundations for what would become the FEH depth-duration-frequency model, evolving from FEH99 to FEH13 and now FEH22. It still offers guidance on estimating Probable Maximum Precipitation.
Volume III: Flood Routing Studies. This volume, led by the Hydraulics Research Station, investigated prediction and estimation of design flood hydrographs and flood routing through physically-based models of river channel flow.
Volume IV: Hydrological Data. This contained the datasets used to conduct the research and which was used for subsequent studies, covering flow and precipitation records from across the UK.
Volume V: Maps. Pretty much what you’d expect, the maps which correspond to the results developed in Volumes I-III, a key reference tool in a pre-digital era.
Continual improvements
Since then, there has been continual improvements to this groundbreaking report. The Institute of Hydrology would continue with work on estimations for small catchments and baseflow, amongst other things. There were retrospectives on the FSR even by 1981, and again in 1987! Nice to know that people were looking at how to improve upon it as soon as it came out; some things never change!
Then in the 1990s, the Institute of Hydrology formed part of the Centre for Ecology & Hydrology, and at a similar time, the next big step was taken: the Flood Estimation Handbook. Another massive undertaking funded by the Ministry of Agriculture Fisheries and Food (MAFF), the Environment Agency, the Department of Agriculture Northern Ireland, and a consortium led by the Scottish Office. This led to a five-volume set that formed the new cornerstone of flood estimation in the UK, and making use of more than 18,000 station-years of data. The FEH boxset still sits pride of place on the shelf above my desk.
As the data grew, so did the computational power to hand: this saw the original version of the WINFAP software developed to help analyse the data and be issued on the first FEH CD-ROM!
Not resting on its laurels, the FEH had more updates with improvements to the rainfall depth-duration-frequency (DDF) model (FEH99), changes to the design flood estimation approach in 2007 leading to the Revitalised FSR rainfall-runoff method, ReFH, and a recalibration of the statistical methods in 2008 (Kjeldsen et al, funded by NERC) now with over 19,600 station-years of data!
By 2013 we had updated the FEH99 model to FEH13 with lots of new data and scientific advancements, and launched the FEH Web Service to replace the piles of CD-ROMs stacked in offices across the land! And in the last few years, we have had the most recent rounds of model updates to FEH22 (rainfall DDF) and the 2025 update to the statistical flood frequency method, using over 28,000 station-years of data this time, and funded directly by UKCEH and the FEH Web Service. This was included in WINFAP5.3, the newest version of our flagship software.
Future plans
So what’s next? Being able to estimate future floods under land, water and atmospheric changes is crucial, and high on our research agenda. Alongside this, we hope to make more use of 15-minute data (UK-Flow15 and Flow Event Data Suite (FEDS) through Hydro-JULES and Flood and Drought Research Infrastructure (FDRI) programmes) to understand more than just flow peaks, but durations, volumes and lags too! I have a long list of research questions that we hope to answer one day.
But we haven’t thrown away anything. All our publications are still available, now for free on the FEH Website, as are the newest updates to the statistical method which came out in 2025, 50 years later! We’re still updating and improving the FEH Web Service with our friends at Wallingford HydroSolutions, alongside the updates of WINFAP 5 and ReFH 2!
UKCEH is proud to have the Flood Studies Report as part of its heritage, and to have worked with more than 100 people who have contributed to it during the last 50 years. I hope that we continue to lead the way in operational flood and rainfall frequency estimation for many years to come. We couldn’t have done it without the support of the Environment Agency, SEPA, NRW, DfI, UKRI, NERC, Wallingford HydroSolutions, the British Hydrological Society, the Institution of Civil Engineers and many more.
