Observed long-term changes in UK river flow patterns: a review

The aim of this paper is to provide a state-of-the-art assessment of the evidence for long-term river flow changes in the UK. This paper necessarily focuses on climate-driven changes in flow, as opposed to capturing changes caused by human influences such as water management practices (e.g. abstraction, discharges, impoundments) or changes in land-use or land management. The paper reviews evidence for changes through the twentieth century, up to the present (2012). However, some consideration is also given to changes earlier than 1900. The focus of the work is on the UK, although a section briefly considers the wider European context. The paper begins with some background on the mechanisms through which climate change may influence river flows, and a description of the data and methods which are commonly used in assessments of hydrological change. The review of the evidence then considers changes in annual and seasonal runoff, high flows and indicators of flooding, low flows and indicators of drought, and river flow trends at the wider European scale. Attribution of observed trends is then discussed, focusing on consistency with observed climate changes, and addressing whether changes can be attributed to anthropogenic warming. Finally, an assessment of confidence in observed changes is made, and knowledge gaps are listed.