Evidence for changes in historic and future groundwater levels in the UK

摘要

We examine the evidence for climate-change impacts on groundwater levels provided by studies of the historicaludobservational record, and future climate-change impact modelling. To date no evidence has beenudfound for systematic changes in groundwater drought frequency or intensity in the UK, but some evidenceudof multi-annual to decadal coherence of groundwater levels and large-scale climate indices has been found,udwhich should be considered when trying to identify any trends. We analyse trends in long groundwater leveludtime-series monitored in seven observation boreholes in the Chalk aquifer, and identify statistically significantuddeclines at four of these sites, but do not attempt to attribute these to a change in a stimulus. The evidence forudthe impacts of future climate change on UK groundwater recharge and levels is limited. The number of studiesudthat have been undertaken is small and different approaches have been adopted to quantify impacts.udFurthermore, these studies have generally focused on relatively small regions and reported local findings.udConsequently, it has been difficult to compare them between locations. We undertake some additional analysisudof the probabilistic outputs of the one recent impact study that has produced coherent multi-site projectionsudof changes in groundwater levels. These results suggest reductions in annual and average summer levels,udand increases in average winter levels, by the 2050s under a high greenhouse gas emissions scenario, at mostudof the sites modelled, when expressed by the median of the ensemble of simulations. It is concluded, however,udthat local hydrogeological conditions can be an important control on the simulated response to a futureudclimate projection.