Hannaford et al. (2025) Have river flow droughts become more severe? A review of the evidence from the UK – a data-rich, temperate environment

Identification

• Journal: Hydrology and earth system sciences
• Year: 2025
• Date: 2025-09-16
• Authors: Jamie Hannaford, Stephen Turner, Amulya Chevuturi, Wilson Chan, Lucy Barker, Maliko Tanguy, Simon Parry, Stuart Allen
• DOI: 10.5194/hess-29-4371-2025

Research Groups

• Water and Climate Science, UK Centre for Ecology & Hydrology, Wallingford, UK
• Irish Climate Analysis and Research UnitS (ICARUS), Maynooth University, Maynooth, Co. Kildare, Ireland
• Evaluation Section, European Centre for Medium-Range Weather Forecasts (ECMWF), Reading, UK
• Chief Scientist’s Group, Environment Agency, Ipswich, UK

Short Summary

This extended review assesses whether river flow droughts in the UK have become more severe, synthesizing existing literature and conducting new analyses. The study finds little compelling evidence of worsening hydrological droughts in the UK, a finding that appears to contradict near-future climate projections and common assumptions about human impacts.

Objective

• To assess whether hydrological droughts in the UK have become more severe over time by synthesizing existing scientific literature and conducting additional analyses on past variability and drivers of change.

Study Configuration

• Spatial Scale: United Kingdom (Great Britain, England, Wales, Scotland), with comparisons to Ireland and wider Europe. Analysis covers 850 catchments across the UK.
• Temporal Scale: Observational period from post-1960 to 2022; centennial-scale changes using reconstructions from 1860 or 1891 to 2015; climate-streamflow relationships analyzed for 1960–2020.

Methodology and Data

• Models used:
  • Statistical water balance model (for Climatic Research Unit (CRU) reconstructions).
  • GR4J hydrological model (for Historic Droughts reconstructions).
  • Grid2Grid distributed model (for MaRIUS project).
  • JULES land surface model (for land cover change scenarios).
• Data sources:
  • Comprehensive literature review.
  • National River Flow Archive (NRFA) for observed river flow data.
  • UK Benchmark Network (UKBN2) and Low-Flow Benchmark Network (LFBN) for near-natural catchments.
  • Published river flow reconstructions (CRU, Historic Droughts, MaRIUS).
  • Standardised Streamflow Index (SSI) and Standardised Precipitation Index (SPI).
  • High-resolution daily gridded precipitation and reconstructed potential evaporation.
  • NOAA’s Extended Reconstructed Sea Surface Temperatures (ERSST), version 5.
  • Environment Agency’s National Abstraction Licensing Database (NALD) and CAMELS-GB dataset for artificial influences.
  • Land cover mapping (e.g., LCM2021) and satellite retrievals for urban cover.
  • Analytical methods: Mann–Kendall (MK) test for monotonic trends, Theil–Sen approach for trend magnitude, Block Bootstrapping (BBS) to account for serial correlation, k-means clustering for regional SSI patterns, and regression analysis for climate-streamflow relationships.

Main Results

• The study found little compelling evidence of widespread worsening hydrological drought or low flows across the UK, despite recent severe drought events (2018, 2022) and future climate projections suggesting increased severity.
• Observed trends (1965–2022) indicate increasing river flows in northern and western Britain, with a mixed pattern in the English lowlands. Seasonal flows show increases in autumn and winter, decreases in spring, and mixed summer patterns.
• Analysis using the 3-month Standardised Streamflow Index (SSI-3) for 1965–2021 showed trends towards decreasing drought severity in the north and west, and a mixed pattern in the southeast, with few statistically significant trends towards worsening drought.
• Centennial-scale reconstructions (1891–2015) also revealed no obvious, discernible trends in hydrological drought, with multi-temporal analysis showing strong sensitivity to the period of analysis and rare statistically significant trends.
• River flow trends are consistent with observed meteorological trends, including wetter winters/autumns, spring drying, and increased spring evapotranspiration.
• Strong associations exist between UK river flows and large-scale atmospheric circulation patterns (North Atlantic Oscillation, East Atlantic pattern, Scandinavia pattern), particularly in winter for northern and western regions.
• Global-scale ocean–atmosphere drivers (e.g., El Niño–Southern Oscillation, Atlantic Multidecadal Oscillation, Pacific Decadal Oscillation, Indian Ocean SSTs) also influence UK droughts, with varying regional and seasonal impacts.
• There is limited scientific evidence conclusively linking artificial influences (e.g., water abstractions, discharges, reservoirs, land use change) to changing hydrological drought patterns in the UK, partly due to data limitations, though some studies suggest detectable impacts on baseflow/low flows.

Contributions

• Provides the first comprehensive, extended review and synthesis of evidence for past variability in hydrological drought across the UK, integrating existing literature with new analyses.
• Presents new multi-temporal trend analyses of observed and reconstructed river flow data and explores global climate teleconnections for UK droughts.
• Highlights a significant discrepancy between observed hydrological drought trends (little evidence of worsening) and near-future climate projections for the UK, offering insights into potential reasons and challenges for water management.
• Emphasizes the critical need for improved data on human interventions and land use/cover changes to better disentangle climate-driven changes from anthropogenic impacts on drought regimes.
• Offers a set of targeted recommendations for future research, including refining drought characterization, extending historical reconstructions, enhancing understanding of climate teleconnections, improving attribution of human impacts, and fostering better reconciliation between observations and models for decision-making.
• Serves as a valuable international case study for assessing changing drought risk in a data-rich, temperate environment.

Funding

• Environment Agency (award no. SC220020)
• UK National Hydrological Monitoring Programme (NERC through the UKCEH National Capability for UK Challenges Programme, grant no. NE/Y006208/1)
• CANARI (grant no. NE/W004984/1)
• Co-Centre for Climate + Biodiversity + Water Programme (grant no. 22/CC/11103) managed by Science Foundation Ireland (SFI), Northern Ireland’s Department of Agriculture, Environment and Rural Affairs (DAERA), and UK Research and Innovation (UKRI; grant no. NE/Y006496/1)

Citation

@article{Hannaford2025Have,
  author = {Hannaford, Jamie and Turner, Stephen and Chevuturi, Amulya and Chan, Wilson and Barker, Lucy and Tanguy, Maliko and Parry, Simon and Allen, Stuart},
  title = {Have river flow droughts become more severe? A review of the evidence from the UK – a data-rich, temperate environment},
  journal = {Hydrology and earth system sciences},
  year = {2025},
  doi = {10.5194/hess-29-4371-2025},
  url = {https://doi.org/10.5194/hess-29-4371-2025}
}