A restatement of the natural science evidence concerning catchment-based 'natural' flood management in the UK.

Flooding is a very costly natural hazard in the UK and is expected to increase further under future climate change scenarios. Flood defences are commonly deployed to protect communities and property from flooding, but in recent years flood management policy has looked towards solutions that seek to mitigate flood risk at flood-prone sites through targeted interventions throughout the catchment, sometimes using techniques which involve working with natural processes. This paper describes a project to provide a succinct summary of the natural science evidence base concerning the effectiveness of catchment-based 'natural' flood management in the UK. The evidence summary is designed to be read by an informed but not technically specialist audience. Each evidence statement is placed into one of four categories describing the nature of the underlying information. The evidence summary forms the appendix to this paper and an annotated bibliography is provided in the electronic supplementary material.

The British river of the future: how climate change and human activity might affect two contrasting river ecosystems in England.

The possible effects of changing climate on a southern and a north-eastern English river (the Thames and the Yorkshire Ouse, respectively) were examined in relation to water and ecological quality throughout the food web. The CLASSIC hydrological model, driven by output from the Hadley Centre climate model (HadCM3), based on IPCC low and high CO(2) emission scenarios for 2080 were used as the basis for the analysis. Compared to current conditions, the CLASSIC model predicted lower flows for both rivers, in all seasons except winter. Such an outcome would lead to longer residence times (by up to a month in the Thames), with nutrient, organic and biological contaminant concentrations elevated by 70-100% pro-rata, assuming sewage treatment effectiveness remains unchanged. Greater opportunities for phytoplankton growth will arise, and this may be significant in the Thames. Warmer winters and milder springs will favour riverine birds and increase the recruitment of many coarse fish species. However, warm, slow-flowing, shallower water would increase the incidence of fish diseases. These changing conditions would make southern UK rivers in general a less favourable habitat for some species of fish, such as the Atlantic salmon (Salmo salar). Accidental or deliberate, introductions of alien macrophytes and fish may change the range of species in the rivers. In some areas, it is possible that a concurrence of different pressures may give rise to the temporary loss of ecosystem services, such as providing acceptable quality water for humans and industry. An increasing demand for water in southern England due to an expanding population, a possibly reduced flow due to climate change, together with the Water Framework Directive obligation to maintain water quality, will put extreme pressure on river ecosystems, such as the Thames.

Current directions in the practice of environmental risk assessment in the United Kingdom.

The manner in which regulators apply environmental risk assessment to their decisions on managing risk is changing. Expectations of risk assessment work are becoming clearer, the social issues agenda is having an impact on risk assessment practice, and there is a trend toward harmonizing approaches to the treatment of environmental risk. For risk analysts, the multiplicity of environmental problems is providing opportunities for the transfer of expertise between the different contexts of applying environmental risk assessment. With the latter as a focus, we summarize recent policy developments in the United Kingdom and illustrate how Government guidance on environmental risk assessment and management is being implemented. We emphasize the need for proportionality in risk analysis, the targeting of regulatory effort to risk, and the explicit treatment of uncertainty. These developments are contributing toward better "risk-informed" environmental decisions in which risk analysis plays an important part alongside other considerations. The forward agenda is likely to see further practical integration between technical risk issues and economic and social concerns, and the positioning of environmental risk assessment within a broader landscape of decision-making tools.