About the Enhanced Future Flows and Groundwater (eFLaG) Portal

The Enhanced Future Flows and Groundwater (eFLaG) Portal is an interactive tool to explore the eFLaG dataset. The dataset is a set of nationally consistent climatological and hydrological projections based on UKCP18 that can be used by the water industry for water resources and drought planning amongst many other uses.

eFlaG contains modelled projections for 200 catchments, 588 groundwater bodies and 54 boreholes covering the UK.

These sites were chosen to reflect the national picture in terms of representation of geographical location, rainfall, soils, altitude and aquifers, and includes catchments that are near-natural and those significantly affected by human activity.

The UKCP18 climate projections of precipitation were bias-corrected (as used in the MaRIUS project, Guillod et al. 2018), and a snow module has been applied at the national scale, to enable the delay of water inputs to the hydrological system when precipitation falls as snow.

The climate projections were then put through hydrological and groundwater models to provide projections of river flows, groundwater levels and groundwater recharge. These are:

The models were calibrated and assessed using observational data (HadUK rainfall, MORECS potential evaporation, the National River Flow Archive and National Groundwater Level Archive) and a common evaluation approach was taken (Smith et al, 2019).

The analysis of the projections as well as transient runs, and model calibration / validation metrics can be explored on the Portal.

Model Drought event characteristics Transient low flows / levels Groundwater recharge Calibration / validation metrics

Drought event characteristics

Using a threshold-based approach drought were identified through the 2018–2090 period and were characterised. The drought characteristics assessed are:

Transient low flows / levels

The 12-member ensemble of transient projections of present and future (up to 2080) daily river flows and groundwater levels are also available to view on the Portal. These have been expressed in flow (or level) percentiles:

They are designed to show the change in yearly low flows (or mean, high etc.) across the period of the projections. All 12 RCM-PPE members are shown and alongside a median of the 12.

Groundwater recharge

Projections of changes in groundwater recharge are available to view on the portal. These are expressed in absolute changes (mm/day) and percentage changes for the 558 groundwater bodies in England Scotland and Wales. The statistics are summarised as monthly averages and seasonal averages.

Calibration / validation metrics

For all models, evaluation was undertaken in two stages, which is typical practice for appraising a model for simulation of climate change impacts:

  1. Evaluation when driven with baseline observed climate data
  2. Evaluation when driven with baseline climate model data.

For Stage 1, a range of metrics are available and widely used to assess how well rainfall-runoff or groundwater models perform against observations. For river flows, these metrics focus on low flows some do evaluate performance across the flow regime. For groundwater levels, a generalised NSE score was used which provides an overall assessment of process realism and fit to groundwater level data. The simulated and observed Standardized Groundwater level Index (SGI) were also compared using the NSE (NSESGI) which focusses in on groundwater extremes including droughts. It is not possible to do a thorough evaluation of the recharge simulations from ZOODRM, given the difficulty in measuring recharge, however, past applications of ZOODRM (e.g. Mansour et al., 2018) have successfully used monthly river flow data as a means to evaluate ZOODRM’s ability to capture catchment water balances and infer the accuracy of seasonal recharge simulations. Accordingly, a subset of the river flow metrics relevant to monthly river flows have been used to evaluate ZOODRM for stage 1.

Stage 2 appraises the performance of the models when driven by the climate model outputs. It compares the simobs and simrcm runs over the common baseline period and instead of metrics the comparison has been done in terms of river flow and groundwater level duration curves. These are to be added to the Portal in due course.

More information about eFLaG

There is a lot more information available on how the data was produced in the open access ESSD Discussions paper (Hannaford et al, 2023).

All the data behind the portal is available to download from the EIDC data pages.

If you would like to submit feedback about the eFLaG Portal, please send it to enquiries@ceh.ac.uk.


The eFLaG Portal was developed in the eFLaG project which was funded by the Met Office through the Strategic Priorities Fund's UK Climate Resilience Programme.


Guillod, B P, Jones, R G, Dadson, S J, Coxon, G, Bussi, G, Freer, J, Kay, A L, Massey, N R, Sparrow, S N, Wallom, D C H, Allen, M R, and Hall, J W. 2018. A large set of potential past, present and future hydro-meteorological time series for the UK, Hydrol. Earth Syst. Sci., 22, 611–634, DOI: 10.5194/hess-22-611-2018.

Hannaford, J, Mackay, J, Ascott, M, Bell, V, Chitson, T, Cole, S, Counsell, C, Durant, M, Jackson, C R, Kay, A, Lane, R, Mansour, M, Moore, R, Parry, S, Rudd, A, Simpson, M, Facer-Childs, K, Turner, S, Wallbank, J, Wells, S, and Wilcox, A. 2023. eFLaG: enhanced future FLows and Groundwater. A national dataset of hydrological projections based on UKCP18, Earth Syst. Sci. Data Discuss. 15, 2391–2415, DOI: 10.5194/essd-2022-40.

Smith, K A, Barker, L J, Tanguy, M, Parry, S, Harrigan, S, Legg, T P, Prudhomme, C, and Hannaford, J. 2019. A multi-objective ensemble approach to hydrological modelling in the UK: an application to historic drought reconstruction, Hydrol. Earth Syst. Sci., 23, 3247–3268, DOI: 10.5194/hess-23-3247-2019.

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