Thursday, 18 October 2012

The future of UK floods and droughts (and the big climate change question)

CEH hydrologist Terry Marsh spent this morning in London briefing members of the press on the facts and figures of UK hydrology throughout 2012. Terry joined staff from the Met Office and the Environment Agency to discuss the transition that has occurred from drought conditions in southern England in early spring, following nearly two years of low rainfall, to one of the wettest periods on record in the last few months.
Terry’s presentation covered the facts and figures of the recent, dramatic hydrological events, putting them into context with the longer term records held within the National Hydrological Monitoring Programme archives at CEH. The discussion at the briefing also touched on the water resources outlook for the winter and 2013, and the longer term question of how the UK should adapt to future changes in flood and drought magnitude and timing.

Floods - are they becoming more common in parts of the UK?

A common question we get asked at CEH is whether floods or droughts are becoming more common in parts of (or all of) the UK. CEH staff regularly publish scientific papers on this subject and a recently published study in the Journal of Hydrology, led by Terry’s colleague at CEH ,Jamie Hannaford, examines the issue in detail.
The new paper, “Trends in seasonal river flow regimes in the UK” (J. Hannaford & G. Buys, Journal of Hydrology), analyses trends over the 1969 – 2008 period in a network of 89 ‘benchmark’ catchments from across the UK. More details can be found in the paper abstract here. The results suggest a much more complex pattern of regional and seasonal variation than revealed in previous work (e.g. two previous papers involving CEH staff published in the International of Journal of Climatology in 2006 and 2008, both of which looked at annual figures from the benchmark catchments as opposed to the seasonal statistics examined in the new paper).
Key conclusions from the new paper include:
·         Some findings resonate with observed rainfall changes, and also with potential future climate change – e.g. increased runoff and high flows in winter and autumn, and decreased flows in spring (but NB. the latter is a result which is sensitive to study period, and is not observed in longer records)
·         In summer, there is no compelling evidence for a decrease in overall runoff or low flows, which is contrary to trajectories of most future projections
The paper abstract concludes:
“Overall, the results do not suggest immediate concern for current water resource management on the basis of observed trends alone: however, the differences between observations and model projections suggest these findings should not be viewed complacently, and greater reconciliation between dataand modelbased assessments should be sought as a basis for informing water management decisions.“
As many have found in the global temperature debate the time series you study has important implications for the conclusions you draw. The Journal of Hydrology paper examined datasets up to the end of 2008 (the scientific paper production process can take a while). Since then we’ve had a sequence of wet summers and drier winters and the CEH team are continuing to work on analysing the latest data, and improving our models, so that our science is better able to inform policy and management decisions.
Additional information

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