Drought resilience and climate change analysis: Moving from a top-down to bottom-up approach in the UK

Water resources across the globe face challenges from population growth and climate change. Concerns regarding the potential implications of extreme, previously unseen, droughts are also increasing. Recent research in the UK has developed and demonstrated new, practical ‘bottom-up’ approaches for assessing and communicating the resilience of water supply systems to droughts beyond the historic record and assessing the potential impacts of climate change. Traditionally water supply planning in the UK has been based around the historic record to identify the worst droughts which in turn are used to test the performance of contemporary water supply systems. Typically, data records extend back to the early twentieth century, although with increasing data uncertainty further back in time, generally providing around five or six events around which to design and plan a water supply system. Drought events are rare and their characteristics are both spatially and temporally variable. Planning solely to events in the historic record does not reflect that droughts in the future could exhibit very different characteristics. Recent work has demonstrated the benefits of using stochastically generated and synthetic droughts applied as part of a ‘bottom-up’ approach to provide a richer understanding of system resilience. The outputs are presented consistently across the industry in the form of drought response surfaces with pragmatic methods and supporting tools developed to support industry application. For climate change, impacts have been previously assessed using ‘top-down’ modelling approaches that, particularly for large, complex conjunctive-use systems, require significant effort regardless of the systems’ potential vulnerability and which may not adequately consider and communicate how adaptation to climate change relates to resilience to droughts. Consequently, further work with the UK water resource industry has extended the “bottom-up” approach to droughts, alongside exploiting previous climate change analysis, to ensure an effective, proportionate approach to climate change. Application of these methods has demonstrated contrasting levels of resilience to different types of droughts and vulnerability to climate change across the UK. The outputs are being used to inform both national policy and underpin local investment planning in demand-side and supply-side measures