Latest dataset shows increase in flooding

The latest peak flow dataset for the UK was released last month by the National River Flow Archive (NRFA). It includes annual maximum river flows up to the water year 2015-16, i.e. including the north of England floods of December 2015.

Duncan Faulkner, Head of Hydrology, will be presenting at the Flood and Coast conference on 22 March on the topic of ‘Is the past still a reliable guide to the future?’.

In the meantime, here are his thoughts on the NFRA dataset trends and the interesting maps we’ve produced with them. Watch out for his journal paper on the dataset too.

JBA Great Britain peak flow trend test results (min 40 yrs)
Great Britain peak flow trend test results (min 40 yrs)

Analysing all river flow gauges in Great Britain with at least 40 years of peak flow data allowed us to test the NFRA dataset for any trends. 23% of the gauges show a statistically significant increasing trend – just 1% show a decrease.

JBA has been pioneering the application of techniques that allow us to incorporate trend in hydrological analysis that underpins decisions about flood risk management. We have been supporting the Environment Agency in planning flood alleviation schemes in parts of England that are seeing upward trends, including Cumbria and Hampshire.

A concentration of upward trends in upland areas is shown in our map and include Cumbria, west Wales, south-west England and parts of Scotland. Strong trends are also seen in some of the chalk catchments of Hampshire and elsewhere in lowland south-east England.

Extent and strength of peak flows increase

Findings match previous research but the extent and strength of trends has increased following the floods of 2012, 2013-14 and 2015, which were not all included in earlier studies of trends.

So, what’s causing the trend? There are a few suspects to consider:

  1. The no. 1 villain – climate change
  2. Changes in rainfall from natural fluctuations between flood-rich and flood-poor periods
  3. Urban development in catchments
  4. Changes in agricultural land use.

Prime suspects for most of the catchments where there are strong upward trends are points 1 and 2. It’s important to try and work out how much of the trend can be attributed to climate change because we can expect this to worsen.

Is the past still a reliable guide to the future?

Duncan’s Flood and Coast conference talk opens the ‘Understanding future flood & coastal risk’ session on the last day of the conference at 2pm in Ludlow Room 3. He will look at the implications of hydrological non-stationarity for flood risk management.

Decisions about investments such as flood alleviation schemes are nearly always based on analysis of information from the past. We assume that past hydrological conditions will be a reasonable guide to what will happen in the future, usually with some adjustment to allow for the possible impacts of climate change. This assumption is becoming increasingly hard to believe given the frequency of severe flooding in some parts of the UK over the past 10-15 years.

Duncan’s presentation describes the application of innovative hydrological methods that break free from the assumption that past floods all follow the same statistical distribution. The results of this non-stationary flood frequency analysis for some rivers in Hampshire, Cumbria and elsewhere show that flood flows for a given probability can be significantly underestimated by conventional methods of flood frequency analysis.

The results have important implications for the appraisal and design of flood protection schemes.

Want to know more?

Email Duncan Faulkner for more information on our work with the datasets or his Flood and Coast presentation. You can also visit our flood and water management web pages to find out more on our work in this area.

Visit us on stand C5

You can speak to our experts at the Flood and Coast conference where you can see demonstrations of our Physical Augmented Relief Model.

Leave a Reply