Gaur et al. (2026) Changes in drought transition dynamics under future climate in Great Britain: A Markov chain analysis using SPI and SSI

Identification

• Journal: Journal of Hydrology
• Year: 2026
• Date: 2026-11-01
• Authors: Nishant Gaur, Encarni Medina-López, Lindsay C. Beevers
• DOI: 10.1016/j.jhydrol.2026.136736

Research Groups

Institute for Infrastructure and Environment, School of Engineering, The University of Edinburgh, United Kingdom.

Short Summary

This study quantifies projected changes in meteorological and hydrological drought transition dynamics across 133 catchments in Great Britain using Standardised Precipitation Index (SPI) and Standardised Streamflow Index (SSI), revealing a significant south-east to north-west contrast in future drought behavior driven by distinct regional mechanisms of drying tendency and persistence.

Objective

• To quantify how conventional drought characteristics (frequency and severity) change under future climate projections across Great Britain.
• To determine if the drought-state transition structure changes significantly between baseline and future periods.
• To identify which components of the transition structure (directional mobility, persistence, or recovery) drive these changes and how they vary regionally.

Study Configuration

• Spatial Scale: 133 parent catchments across Great Britain, with hydrological modeling on a 1 km resolution grid.
• Temporal Scale:
  • Data Period: December 1980 to November 2080 (precipitation), December 1982 to November 2080 (streamflow).
  • Study Periods: Baseline (1989-2018), Near-Future (2020-2049), Far-Future (2050-2079).
  • Drought Time Scales: 1-month, 6-month, and 18-month accumulation periods for SPI and SSI.

Methodology and Data

• Models used:
  • Hydrological Models (HMs): Grid-to-Grid (G2G), Probability Distributed Model (PDM), GR4J, GR6J.
  • Climate Model: UKCP18 Regional Climate Model (RCM) projections (12 ensemble members).
  • Drought Analysis: First-order Markov chain (MC) analysis for drought state transitions.
• Data sources:
  • Enhanced Future Flows and Groundwater (eFLaG) dataset for precipitation and river flow simulations.
  • UKCP18 regional climate projections for precipitation.
  • Catchment-average time series derived using the UK National River Flow Archive (NRFA) approach.

Main Results

• Conventional drought characteristics (frequency and severity) show a clear south-east to north-west contrast, with southern catchments becoming more drought-prone and severe, while many north-western catchments show weaker changes or reductions.
• Drought state transition structures change significantly under future climates, with a robust north-south contrast: southern catchments exhibit a stronger and more consistent ensemble signal of change, particularly at longer timescales, compared to weaker or more heterogeneous responses in northern catchments.
• Southern and south-eastern catchments show stronger increases in downward mobility (tendency towards drier states) and reduced upward mobility (weaker recovery), indicating a systematic shift towards drier conditions.
• The strongest increases in dry-to-dry persistence (tendency to remain in dry states) are observed in parts of south-western Great Britain, indicating that directional drying and dry-state persistence peak in different regions.
• Some western catchments exhibit simultaneous increases in both dry-to-dry and wet-to-wet persistence, suggesting a more "sticky" transition structure at hydroclimatic extremes.

Contributions

• This study provides the first unified SPI–SSI analysis of future drought-transition dynamics in Great Britain.
• It addresses the gap in understanding how drought states evolve over time by quantifying projected changes in drought transition dynamics, beyond conventional frequency and severity metrics.
• It systematically examines future changes in drought category transition dynamics for both meteorological (SPI) and hydrological (SSI) drought within a unified framework for Great Britain.
• The research decomposes Markov chain transition matrices into diagnostic metrics (downward mobility, upward mobility, dry-to-dry persistence, wet-to-wet persistence) to identify the underlying drivers of change, a novel application in Great Britain's drought literature.
• It reveals that future drought intensification may arise through different transition mechanisms across Great Britain, with directional drying and dry-state persistence peaking in distinct regions, offering a process-based perspective for drought-risk assessment and water management.

Funding

Not explicitly stated in the provided text.

Citation

@article{Gaur2026Changes,
  author = {Gaur, Nishant and Medina-López, Encarni and Beevers, Lindsay C.},
  title = {Changes in drought transition dynamics under future climate in Great Britain: A Markov chain analysis using SPI and SSI},
  journal = {Journal of Hydrology},
  year = {2026},
  doi = {10.1016/j.jhydrol.2026.136736},
  url = {https://doi.org/10.1016/j.jhydrol.2026.136736}
}