Projecting extreme droughts in rapidly changing human-water systems

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A reliable water supply is usually taken for granted in the UK. However, there is increasing pressure on water supplies. By 2050, anthropogenic climate change and increasing water demand from a growing population is projected to lead to frequent water shortages across the UK, with projections estimating more than 3 billion litres of additional water a day required to ensure supply. An extreme drought could exceed the coping capacity of many water companies leading to severe supply restrictions and costing up to £40 billion in emergency water supply measures alone. Predicting plausible 'worst case' droughts and their impacts on river flows is vital to test the resilience of current water supply systems, to support critical planning decisions such as future investment in supply infrastructure (e.g. reservoirs, desalination plants, inter-catchment water transfer schemes) and to ensure adequate future water supply for food-energy-water systems. This is a challenge as current understanding of how freshwater resources will respond to changes in water supply and water demand remain poorly understood and quantified, particularly for extreme drought events. The problem is two-fold. Firstly, the models we currently use to inform water resource decisions currently neglect key interactions between human water-use (such as reservoir storage, irrigation, hydro-power generation) and terrestrial water fluxes (such as hillslope runoff, surface water and groundwater flow). Secondly, such extreme drought events are especially difficult to characterise and predict. Droughts are complex phenomena that vary across multiple spatial and temporal scales from small river reaches to continental scales lasting for weeks to decades.This research addresses these challenges by establishing the resilience of water systems across Great Britain to extreme droughts. It will develop new integrated modelling tools and leverage unique datasets of human-water use to determine how freshwater resources (river flows and groundwater levels) will respond to changes in water supply (from anthropogenic climate change) and water demand (from human water use). The integrated modelling framework will explicitly characterise the interactions and feedbacks between human-water use (from domestic, agricultural and industrial demand) and hydro-climatic processes (land-atmosphere, hillslope runoff and surface-groundwater interactions). This will be used to facilitate a step-change in UK drought prediction and generate new understanding of how human-water interactions alleviate or enhance hydrological droughts that will feed into the next generation of earth system models. I will develop nationally consistent, open access libraries of meteorological and hydrological drought events to provide the first extreme drought projections for Great Britain that account for changes in future water supply and demand. These new datasets will be used to support critical decisions on how best to manage future water resources in collaboration with key project partners including water companies, regional planning groups, regulatory bodies and research institutes.