To forecast groundwater levels the British Geological Survey uses models that simulate fluctuations in groundwater level at 25 sites across the UK. Each of these models is driven by rainfall and evaporation time-series and has been calibrated against past observations of groundwater level.
To forecast the change in groundwater level at a site over the coming one and three months we make use of 1 and 3-month ahead climate forecasts produced by a Met Office climate model.
These two climate forecasts are probabilistic. Each consists of an ensemble of up to 42 members and each member provides a projection of rainfall and temperature into the future. Each member of the two climate forecast ensembles is run through each groundwater model. Consequently, a probabilistic groundwater level forecast is produced for each site.
BGS produces forecasts at sites located in most of the principal aquifers of the UK but currently not all; sites in some aquifers, where groundwater abstraction has significantly modified the observed groundwater level hydrograph, have not been modelled yet.