Yang et al. (2026) Stepwise-clustered downscaling of spatiotemporal variations in compound drought-heatwave extremes over the Yangtze River Basin

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-09-26
• Authors: Zhirui Yang, Ya Zhou, Guohe Huang, Yongping Li, Xiong Zhou, Jiayan Ren, Feng Wang, Yiting Wei, Xinyue Ren
• DOI: 10.1016/j.ejrh.2026.104015

Research Groups

• State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of Environment, Beijing Normal University, Beijing, China
• School of Systems Science, Beijing Normal University, Beijing, China
• Institute of Non-Equilibrium Systems, Beijing Normal University, Beijing, China
• Center for Energy, Environment and Ecology Research, UR-BNU, School of Environment, Beijing Normal University, Beijing, China
• School of urban and rural planning, Henan University of Economics and Law, Zhengzhou, China

Short Summary

This study developed a Stepwise Clustering Drought-Heatwave Downscaling (SCDHD) framework to project compound drought-heatwave (CDHW) variations across the Yangtze River Basin (YRB) at the station scale under SSP2-4.5 and SSP5-8.5. It found that under SSP5-8.5, CDHW frequency declines overall, but maximum duration, mean duration, and mean event intensity significantly increase, underscoring the necessity of multiple complementary indicators for comprehensive hazard assessment.

Objective

• To establish station-scale downscaling models for daily maximum temperature, precipitation, and potential evapotranspiration.
• To assess future changes in CDHW frequency, maximum duration, mean duration, and mean event intensity under SSP2-4.5 and SSP5-8.5.
• To characterize CDHW heterogeneity across the YRB, its five climatic regions, and 12 representative stations.
• To compare the responses of frequency, duration, and intensity to different emission scenarios.

Study Configuration

• Spatial Scale: Yangtze River Basin (YRB), divided into five climatic regions (Humid Delta, Semi-Humid Plain, Semi-Humid Hill, Semi-Humid Basin, Semi-Arid Plateau), analyzed at 12 meteorological stations (station-scale downscaling).
• Temporal Scale: Historical baseline (1985–2014), near-future (2031–2060), and late-century (2061–2090) periods, with daily time steps for CDHW identification and annual/30-year period-based comparisons.

Methodology and Data

• Models used:
  • Stepwise Clustering Drought-Heatwave Downscaling (SCDHD) framework.
  • Stepwise Cluster Analysis (SCA) using the rSCA package for downscaling.
  • Five CMIP6 Global Climate Models (GCMs): CanESM5, INM-CM5–0, MPI-ESM1–2-LR, NorESM2-LM, and TaiESM1.
  • Multi-model ensemble mean (MME).
  • Standardized Precipitation Evapotranspiration Index (SPEI) based on a 30-day rolling accumulation window.
  • FAO Penman–Monteith method for potential evapotranspiration (PET) calculation.
  • Mann–Kendall test and Sen’s slope for trend analysis.
  • Locally weighted scatterplot smoothing (LOWESS).
• Data sources:
  • Observed data: China Ground Climate Data Daily Dataset from the National Meteorological Information Center (NMIC).
  • Reanalysis data: Hourly ERA5 data from the European Centre for Medium-Range Weather Forecasts (ECMWF) for 1985–2014.
  • Climate model data: Daily outputs from five CMIP6 models under SSP2–4.5 and SSP5–8.5 scenarios from the CMIP6 archive.

Main Results

• The SCDHD framework reasonably reproduced historical climate variables (daily maximum temperature, precipitation, potential evapotranspiration) and key drought and heatwave characteristics.
• Daily maximum temperature is projected to increase at all stations under both scenarios: 1.8–2.6 °C under SSP2-4.5 and 3.7–5.1 °C under SSP5-8.5. Precipitation shows an overall increasing trend, particularly in summer, while potential evapotranspiration changes are less pronounced.
• Under SSP2–4.5, CDHW frequency increased by 0.116 events per decade, with maximum duration increasing by 0.978 days per decade, mean duration by 0.707 days per event per decade, and mean event intensity by 1.481 °C·day per event per decade.
• Under SSP5–8.5, CDHW frequency declined overall by 0.167 events per decade, but maximum duration increased by 1.406 days per decade, mean duration by 1.268 days per event per decade, and mean event intensity by 4.667 °C·day per event per decade.
• Regional analysis revealed heterogeneous changes: under SSP2-4.5, frequency increased in Semi-Humid Hill, Semi-Humid Basin, and Semi-Arid Plateau, but decreased in Humid Delta and Semi-Humid Plain. Under SSP5-8.5, frequency decreased in most regions except Semi-Arid Plateau. Duration and intensity generally increased across regions under both scenarios, with larger increases under SSP5-8.5.
• The contrasting changes in frequency, duration, and intensity, particularly under SSP5-8.5, demonstrate that fewer events can coexist with longer-lasting and more intense individual events, highlighting the need for multiple complementary indicators to characterize future CDHW hazards.

Contributions

• Developed a novel Stepwise Clustering Drought-Heatwave Downscaling (SCDHD) framework that integrates multivariable statistical downscaling with daily compound-event analysis to provide high-resolution climate information.
• Provided detailed, station-scale future projections of compound drought-heatwave events (CDHWs) across the Yangtze River Basin, resolving scenario-dependent and regional differences not captured by basin-wide averages.
• Demonstrated that an overall decline in CDHW frequency can coexist with increasing event duration and mean accumulated thermal exceedance under high-emission scenarios, emphasizing the critical need for joint assessment of frequency, persistence, and thermal intensity for comprehensive hazard characterization.
• Supported differentiated adaptation planning across the YRB by identifying regional contrasts in CDHW behavior, linking specific hazards to heat preparedness, agricultural drought management, and water-resource/ecosystem management.

Funding

• Natural Science Foundation (52279002, 52279003, 52221003)
• National Key R&D Program (2023YFC3206503)
• Natural Science and Engineering Research Council of Canada

Citation

@article{Yang2026Stepwiseclustered,
  author = {Yang, Zhirui and Zhou, Ya and Huang, Guohe and Li, Yongping and Zhou, Xiong and Ren, Jiayan and Wang, Feng and Wei, Yiting and Ren, Xinyue},
  title = {Stepwise-clustered downscaling of spatiotemporal variations in compound drought-heatwave extremes over the Yangtze River Basin},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2026.104015},
  url = {https://doi.org/10.1016/j.ejrh.2026.104015}
}