How will climate change affect spatial coherence of streamflow and groundwater droughts in Great Britain?

How climate change will affect spatial coherence of droughts is a key question that water managers must answer in order to adopt strategies to mitigate impacts on water resources. For example, water transfers between regions have long been considered as a possible water management option. Conjunctive use of surface water and groundwater is another common water management practice. However, in both cases, these solutions are only viable if both regions or stores are not in drought simultaneously. These relationships might change under the influence of climate change.

The recently published ‘enhanced Future Flows and Groundwater’ (eFLaG) dataset of nationally consistent hydrological projections for the UK, based on the latest UK Climate Projections (UKCP18), provides the opportunity to explore the future evolution of drought spatial coherence in detail. Here, we use eFLaG future simulations of streamflows and groundwater levels to analyse the projected change in drought spatial coherence in Great Britain, over its seven different water regions, using joint and conditional probabilities of occurrence. Some key findings are: an increase in coherence in summer everywhere in the country; in winter, however, it will only increase in the South-East; and, in most regions, the coherence between groundwater and streamflow droughts will increase, one exception being the South-East in summer.

These results provide valuable insight to water managers to inform their long-term strategies to overcome future impacts of droughts. The methodology has the potential to be applied to other parts of the world to help shape strategic regional and national investments to increase resilience to droughts.