The Spatial Dynamics of Droughts and Water Scarcity in England and Wales

Water scarcity occurs when water demand exceeds natural water supply over a range of spatial and temporal scales. Though meteorological and hydrological droughts have been analysed over large spatial scales, the impacts of water scarcity have typically been addressed at a catchment scale. Here we explore how droughts and water scarcity interact over a larger and more complex spatial domain, by combining climate, hydrological and water resource system models at a national scale across England and Wales. This approach is essential in a highly connected and heterogeneous region like England and Wales, where we represent 80 different catchments; 70 different water resource zones; 16 water utility companies and the water supply for over 50 million people. We find that, if a reservoir’s storage is in its 1st percentile (i.e. the volume that is exceeded 99% of the time), then there is, on average, a 40% chance that reservoirs in neighbouring catchments will also be in their 1st percentile. The coincidence of reservoir storage decays relatively quickly, stabilising after about 100-150km, implying that if inter-basin transfers are to be provided to enhance drought resilience, they will need to be at least this length. Based on a large ensemble of future climate simulations, we show that extreme droughts in precipitation, streamflow and reservoir storage volume are projected to worsen in every catchment. The probability of a year with water use restrictions doubles by 2050 and is four times worse by 2100.