enhanced future FLows and Groundwater (eFLaG): future hydrological projections to enhance drought resilience in the UK

Water resource managers all over the world require timely and robust climate projections to support planning on a range of timescales. In the UK, water companies are obliged to produce long-term water resource management plans to ensure security of water supply, and these are required to take account of climate change. One of the challenges is having ready access to the latest climate projections, at an appropriate scale to support regional- and national-scale planning. In particular, a major gap has been the availability of a national, spatially-coherent dataset of river flows and groundwater projections.

This presentation introduces the ‘enhanced Future Flows and Groundwater’ (eFLaG) project, that has delivered nationally consistent hydrological (river flow and groundwater) projections for the UK, based on the latest UK Climate Projections (UKCP18). The hydrological projections are derived from an ensemble of river flow models (Grid-to-Grid, PDM, GR4J and GR6J) and groundwater models (AquiMod and ZOODRM) to provide an indication of hydrological model uncertainty. A 12-member ensemble of transient projections of present and future (up to 2080) daily river flows, groundwater levels and groundwater recharge were produced using bias-corrected data from the UKCP18 Regional (12km) climate ensemble. Projections are provided for 200 river catchments, 54 groundwater level boreholes and 558 groundwater bodies sampling across the diverse hydrological and geological conditions of the UK. An evaluation, using multiple metrics, will be presented for the national scale.

The eFLaG project also undertook a national-scale analysis of hydrological droughts. We present results showing the future evolution of hydrological drought severity compared to a current baseline – generally showing significant increases in drought severity in future. We also show the evolution of low flows through the 21^st century, demonstrating the benefit of having long, transient ensemble runs of river flows and groundwater levels. While there are wide uncertainties, reflecting the diversity of RCM ensemble members and hydrological models alike, generally these results point towards decreasing low flows and minimum groundwater levels through the coming century. Finally, we also undertook an analysis of spatial coherence of drought, showing how inter-regional coherence of drought changes under anthropogenic warming – results which could have implications for water transfers that are integral to the latest round of Water Resources Management Plans (WRMPs).

eFLaG is designed to provide a demonstration climate service to enhance the resilience of the water sector to drought events. In this regard, we will also describe three contrasting case studies (Thames, Wales and Scotland) where the team collaborated with the water industry to demonstrate the utility of eFLaG for water resources management applications. These demonstrators illustrate the potential benefit of coherent, multimodel, transient projections, while also the challenges in integrating them with current statutory WRMPs produced by water companies.

While eFLaG was developed with drought applications as the primary focus, the evaluation metrics show that river flows and groundwater levels are generally well simulated across the regime. The eFLaG dataset can potentially be applied to a wider range of water resources research and management contexts, pending a full evaluation for the designated purpose.