The impacts of urbanisation and climate change on urban flooding and urban water quality: A review of the evidence concerning the United Kingdom

United Kingdom (UK). Climate change and urbanization pose significant threats for flooding and water quality in urban areas. This paper reviews the evidence concerning the combined impacts of urbanisation and climate on the urban water environment of inland catchments of the United Kingdom and assesses the degree of confidence in reported directions of change and response. It also assesses the utility of the evidence for setting environmental legislation and managing the urban water environment in the future and identifies knowledge gaps that limit effective and management interventions. There is a lack of nationally research focused on the dual impacts of climate change and urbanisation on flooding and water quality in UK urban areas. This is despite there being a clear acceptance that flood risk is increasing, water quality is generally not meeting desirable levels, and that combined population and climate change projections pose a pressing challenge. The available evidence has been found to be of medium-high confidence that both pressures will result in (i) an increase in pluvial and fluvial flood risk, and (ii) further reduction in water quality caused by point source pollution and altered flow regimes. Evidence concerning urban groundwater flooding, diffuse pollution and water temperature was found to be more sparse and was ascribed a low-medium confidence that both pressures will further exacerbate existing issues. The confidence ascribed to evidence was also found to reflect the utility of current science for setting policy and urban planning. Recurring factors that limit the utility of evidence for managing the urban environment includes: (i) climate change projection uncertainty and suitability, (ii) lack of sub-daily projections for storm rainfall, (iii) the complexity of managing and modelling the urban environment, and (iv) lack of probable national-scale future urban land-use projections. Suitable climate products are increasingly being developed and their application in applied urban research is critical in the wake of a series of extreme flooding events across the UK and timely for providing state-of-the-art evidence on which to base possible future water quality legislation in a post Brexit-WFD era.