Using high-resolution climate change information in water management: a decision-makers' perspective.

The UK Climate Change Act requires the Environment Agency to report the risks it faces from climate change and actions taken to address these. Derived information from projections is critical to understanding likely impacts in water management. In 2019, the UK published an ensemble of high-resolution model simulations. The UKCP Local (2.2 km) projections can resolve smaller scale physical processes that determine rainfall and other variables at subdaily time-scales with the potential to provide new insights into extreme events, storm runoff and drainage management. However, simulations also need to inform adaptation. The challenge ahead is to identify and provide derived products without the need for further analysis by decision-makers. These include a wider evaluation of uncertainty, narratives about rainfall change across the projections and bias-corrected datasets. Future flood maps, peak rainfall estimates, uplift factors and future design storm profiles also need detailed guidance to support their use. Central government support is justified in the provision of up-to-date impacts information to inform flood risk management, given the large risks and exposure of all sectors. The further development of projections would benefit from greater focus and earlier scoping with industry representatives, operational tool developers and end users. This article is part of a discussion meeting issue 'Intensification of short-duration rainfall extremes and implications for flash flood risks'.

A novel application of remote sensing for modelling impacts of tree shading on water quality.

Uncertainty in capturing the effects of riparian tree shade for assessment of algal growth rates and water temperature hinders the predictive capability of models applied for river basin management. Using photogrammetry-derived tree canopy data, we quantified hourly shade along the River Thames (UK) and used it to estimate the reduction in the amount of direct radiation reaching the water surface. In addition we tested the suitability of freely-available LIDAR data to map ground elevation. Following removal of buildings and objects other than trees from the LIDAR dataset, results revealed considerable differences between photogrammetry- and LIDAR-derived methods in variables including mean canopy height (10.5 m and 4.0 m respectively), percentage occupancy of riparian zones by trees (45% and 16% respectively) and mid-summer fractional penetration of direct radiation (65% and 76% respectively). The generated data on daily direct radiation for 2010 were used as input to a river network water quality model (QUESTOR). Impacts of tree shading were assessed in terms of upper quartile levels, revealing substantial differences in indicators such as biochemical oxygen demand (BOD) (1.58-2.19 mg L-1 respectively) and water temperature (20.1 and 21.2 °C respectively) between 'shaded' and 'non-shaded' radiation inputs. Whilst the differences in canopy height and extent derived by the two methods are appreciable they only make small differences to water quality in the Thames. However such differences may prove more critical in smaller rivers. We highlight the importance of accurate estimation of shading in water quality modelling and recommend use of high resolution remotely sensed spatial data to characterise riparian canopies. Our paper illustrates how it is now possible to make better reach scale estimates of shade and make aggregations of these for use at river basin scale. This will allow provision of more effective guidance for riparian management programmes than currently possible. This is important to support adaptation to future warming and maintenance of water quality standards.

Risks posed by climate change to the delivery of Water Framework Directive objectives in the UK.

The EU Water Framework Directive (WFD) is novel because it integrates water quality, water resources, physical habitat and, to some extent, flooding for all surface and groundwaters and takes forward river basin management. However, the WFD does not explicitly mention risks posed by climate change to the achievement of its environmental objectives. This is despite the fact that the time scale for the implementation process and achieving particular objectives extends into the 2020s, when climate models project changes in average temperature and precipitation. This paper begins by reviewing the latest UK climate change scenarios and the wider policy and science context of the WFD. We then examine the potential risks of climate change to key phases of the River Basin Management Process that underpin the WFD (such as characterisation of river basins and their water bodies, risk assessments to identify pressures and impacts, programmes of measures (POMs) options appraisal, monitoring and modelling, policy and management activities). Despite these risks the WFD could link new policy and participative mechanisms (being established for the River Basin Management Plans) to the emerging framework of national and regional climate change adaptation policy. The risks are identified with a view to informing policy opportunities, objective setting, adaptation strategies and the research agenda. Key knowledge gaps have already been identified during the implementation of the WFD, such as the links between hydromorphology and ecosystem status, but the overarching importance of linking climate change to these considerations needs to be highlighted. The next generation of (probabilistic) climate change scenarios will present new opportunities and challenges for risk analysis and policy-making.