Drought variability in a wet country (the UK): when observation-based trends and hydroclimate projections disagree, how might we move forward?

Whenever record-breaking flood and drought events occur, they are held up as a manifestation of anthropogenic warming – which is entirely reasonable given physical reasoning and typical projections for the future. However, to contextualise such claims it is also vital to analyse long-term observations of river flow to detect and attribute emerging trends. While there is often good agreement between these lines of evidence, there are sometimes discrepancies in the strength or even the direction of change in observations compared to climate projections. This can present a profound challenge to policymakers and adaptation planners: how to proceed given deep uncertainty in future projections, especially if conflicting with lived historical experience?

In this presentation, we tackle this question using hydrological droughts in the UK as a case study. Recent major droughts[LB1]  (including in 2025) have led to growing concerns that droughts are becoming more severe in the UK, despite it generally being perceived as a wet country. Firstly, we appraise the evidence for any trends towards worsening hydrological droughts in the UK. The UK has a well-established monitoring programme and hence provides a good international case study for addressing this question. We assess the evidence for changes in the well-gauged post-1960 period, before considering centennial scale changes using reconstructions. A further challenge with hydrological extremes (compared to climate variables) is that observed trends in river flows can reflect catchment alterations rather than climatic variability. Hence, we provide a synthesis of our understanding of the drivers of change in hydrological drought, both climatic and in terms of direct human disturbances to river catchments (e.g. changing patterns of water withdrawals, impoundments, land use changes). These latter impacts confound the identification of climate-driven changes, and yet human influences are themselves increasingly recognised as potential agents of changing drought regimes. Perhaps surprisingly, we find little evidence of compelling changes towards worsening drought, apparently at odds with climate projections for the relatively near future and widely-held assumptions of the role of human disturbances in intensifying droughts. Nevertheless it leaves water managers and policymakers at an impasse.

Hence, we set out recommendations for guiding research and policy alike. Two major themes emerge: 1) integration of observational trend studies with hydroclimate modelling using ‘large ensemble’ approaches, seeing the observed past as only one instance among ‘worlds that might have been’ to help better frame emerging risks and develop stress tests; 2) improved understanding of the drivers of change, moving beyond largely correlation-based links with climate forcings towards understanding underlying atmosphere-oceanic processes, while simultaneously better discriminating the ‘human factor’ (i.e. water withdrawals or land use) – a grand challenge but one which new datasets and methods are making more feasible. While our focus is the UK, we envisage the themes within this presentation will resonate with the international community and we conclude with ways our findings are relevant more broadly.