Flooding in the UK: ecological impacts and an ecosystem approach

During Christmas and New Year, the news in the UK was dominated by one topic: flooding. Across the north of England, north Wales, and parts of Scotland, homes and communities have been devastated by extreme floods, with river levels reaching record highs in many areas. December 2015 was the warmest on record across the UK, an extraordinary 4.1°C above the long-term average, and the wettest on record in Scotland, Wales and North West England. Over 16,000 homes have been flooded, with insurance claims for damages expected to reach over £1.3 billion.

As expected, the political ramifications of the floods have been significant, with arguments swirling over whether or not the Government has invested sufficiently in flood defences, the effectiveness of natural flood management vis-à-vis hard engineering approaches such as dredging, and the role of climate change in causing the floods. A National Flood Resilience Review has been launched, and the Environment Agency has called for a “complete rethink” of the UK’s approach to flood defence.

The impact of extreme events on freshwater ecosystems

Understandably, and correctly, the main focus of the debate so far has been the impact of flooding on human lives and livelihoods. But what is the ecological impact of severe flooding? This topic was addressed in detail in our 2013 Ecological Issues report, and accompanying policy brief, on The Impact of Extreme Events on Freshwater Ecosystems.

Freshwater ecosystems are rich in biodiversity, and also provide a wealth of ecosystem services from which humans benefit, including the provision of fresh water, huge recreational and aesthetic value, and flood control. Disturbance, in the form of floods or droughts, are a natural part of these ecosystems, and play an important role in creating and regenerating habitats. However, extreme climatic events, of the level seen in the UK this winter, may cause irrevocable damage to ecosystems, potentially even shifting them into an alternate state.

Climate change means that these extreme events, which push ecosystems beyond the threshold of normal disturbance, are set to become more frequent. In fact, as our report states, the increase in the number and severity of extreme events are likely to be “the most profound effects of climate change on freshwater ecosystems”. While it is impossible to ascribe any single weather event to climate change, the Met Office has concluded that, “it is entirely plausible that climate change has exacerbated what has been a period of very wet and stormy weather arising from natural variability”

Extreme flood events have a number of negative impacts on freshwater ecosystems. Floods increase surface run-off, exacerbating erosion and introducing more soil, organic matter and pollutants into water courses, whilst erosion within the river channel is also increased. Previous studies have shown that plant biomass and the abundance of both vertebrates – such as fish – and invertebrates can be dramatically reduced by extreme floods. For example, populations of the freshwater pearl mussel – an endangered species found in the north of the UK – can be significantly affected by extreme floods, which remove mussels from river beds and increase riverine pollution.

While some extreme events may force ecosystems over a threshold beyond which a different, simpler community of species forms, in many cases a process of natural recovery will take place. However, this resilience to extreme events is greatest where active natural processes proceed relatively unhindered; where freshwater ecosystems have been degraded by human impacts, be that through pollution or physical damage to habitats, the ability of the system to recover will be highly compromised. Management strategies that seek to improve connectivity of habitats, and provide refuges available to species during flood events will increase ecosystem resilience, and the consequent recovery of the vital services to people that freshwater systems provide.

An ecosystem approach for people and nature?

The Impact of Extreme Events on Freshwater Ecosystems makes it clear that extreme floods of the type recently experienced in the UK can have negative consequences for both ecosystems and people. However, in much of the media debate following the floods, people and nature have been set in opposition; presented as an “either/or”. This false dichotomy was underlined this week by David Cameron, who told the House of Commons Liaison Committee that an “attitudinal change” was required in our approach to flooding, away from “trying to balance up the effects on nature on the one hand and protecting property on the other”, towards a primary focus on “protecting human lives”.

Yet elsewhere in the same evidence session, the Prime Minister hinted towards an approach to flood management that did not put people and the environment at loggerheads. He suggested solutions including looking “at the way whole drainage and area systems work”, “slowing the water down”, and “upstream attenuation ponds and farming practices to try to hold on to the water”. These ideas go some way towards the ecosystem approach to managing freshwater ecosystems highlighted in our report. This approach integrates assessment and management of land, water and living resources, and requires consideration of how human actions affect the interconnected components of an ecosystem.

An ecosystem approach to flood management would seek to work with the environment to manage land and water in ways that benefit people and ecosystems. There is growing, if still incomplete, evidence, for the ability of natural flood management approaches – slowing water down, encouraging infiltration and harnessing natural processes – to mitigate the flooding impact of extreme events, whilst also supporting healthy, resilient ecosystems: a potential “win-win” situation.

That isn’t to say that there isn’t still an important role for more conventional flood defences, or that there won’t be cases where difficult trade-offs have to be made in order to protect homes and businesses. There is no single solution to complex challenges such as flooding; more research is needed as to the efficacy of different flood management techniques, and to better monitor and understand the impact of extreme events on freshwater ecosystems. However, it is clear that an evidence-informed (rather than anecdote-led), integrated approach, working across catchments and with, not against nature, offers a more sustainable solution to dealing with the devastating impact of flooding.

Download Ecological Issues: The Impact of Extreme Events on Freshwater Ecosystems

Download The Impact of Extreme Events on Freshwater Ecosystems executive summary and policy brief