Qi et al. (2026) Climate change overrides population dynamics in driving flood exposure in the Yangtze River Basin

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-04-07
• Authors: Wei Qi, Libin Lu, Yanpeng Cai, Qian Tan
• DOI: 10.1016/j.ejrh.2026.103418

Research Groups

• Guangdong Basic Research Center of Excellence for Ecological Security and Green Development, School of Ecology, Environment and Ocean, Guangdong University of Technology, Guangzhou 510006, China

Short Summary

This study quantifies future population exposure to river floods in the Yangtze River Basin under various climate change and socioeconomic scenarios, finding that climate change is the dominant driver of increased exposure, particularly in the middle and lower reaches, overriding population dynamics at higher warming levels.

Objective

• To quantify future population exposure to river floods in the Yangtze River Basin under different climate change and socioeconomic development pathways.
• To decompose the relative contributions of climate-driven changes in flood hazard and population dynamics to future exposure.
• To evaluate exposure trajectories across conventional time slices and discrete global warming levels from 1.5 °C to 4.5 °C above pre-industrial conditions.

Study Configuration

• Spatial Scale: Yangtze River Basin (approximately 1.8 × 10^6 square kilometers), analyzed at a 0.1° latitude-longitude grid resolution and sub-basin scale.
• Temporal Scale:
  • Historical: 1985–2014
  • Near-future: 2036–2065
  • Far-future: 2071–2100
  • Global Warming Levels: 1.5 °C, 2.0 °C, 2.5 °C, 3.0 °C, 3.5 °C, 4.0 °C, and 4.5 °C above pre-industrial conditions (30-year windows around the year each level is reached).

Methodology and Data

• Models used:
  • Hydrological model: WEB-DHM-SG (distributed hydrological model).
  • Climate projections: Inter-Sectoral Impact Model Intercomparison Project phase 3b (ISIMIP3b) bias-corrected climate fields from an ensemble of five General Circulation Models (GCMs): GFDL-ESM4, IPSL-CM6A-LR, MPI-ESM1–2-HR, MRI-ESM2–0, and UKESM1–0-LL.
• Data sources:
  • Historical climate forcing: APHRODITE and China Meteorological Forcing Data.
  • Future climate forcing: ISIMIP3b bias-corrected GCM outputs (re-gridded from 0.5° to 0.1°).
  • Population data: Gridded population datasets consistent with Shared Socioeconomic Pathways (SSPs) at 0.1° resolution (aligned with Jiang et al. 2020 and Su et al. 2018), incorporating domestic demographic shifts.
  • Socioeconomic scenarios: SSP126 (SSP1-2.6), SSP370 (SSP3-7.0), and SSP585 (SSP5-8.5).
  • Flood exposure calculation: Annual maximum daily exposed population, calculated as population multiplied by flood inundation area fractions in each grid cell.
  • Decomposition analysis: Comparison of a combined experiment (climate and population change) with a fixed-population experiment (climate change only, population held constant at 2010–2019 mean distribution).
  • Statistical analysis: Mann–Kendall test for trend significance and ordinary least-squares regression.

Main Results

• Basin-wide population exposure to floods is projected to increase sharply from approximately 30 million people historically to roughly 50 million people in the near-future across all SSP scenarios.
• By the far-future (2071–2100), exposure remains about 35–40% above historical levels under SSP126 and SSP585, but nearly doubles under SSP370.
• High-exposure and strongly increasing sub-basins are consistently concentrated in the middle and lower-reach floodplains, while many upper-reach sub-basins show decreasing exposure, reinforcing upstream–downstream inequalities.
• Climate change is the dominant driver of long-term exposure increases at the basin scale, shifting the Yangtze River Basin from a low- to a high-exposure regime.
• Population dynamics primarily modulate exposure at low warming levels (1.5–2.5 °C), contributing to positive amplification, but play a minor or compensating role at higher warming levels (3.5–4 °C), with a negative contribution.
• The most significant increase in basin-wide exposure occurs between the historical climate and 1.5 °C warming; additional warming from 1.5 °C to 4.5 °C results in only modest further changes, maintaining a high but relatively stable plateau.

Contributions

• Provides a high-resolution (0.1°) basin-scale, exposure-focused assessment for the Yangtze River Basin, addressing previous studies' limitations of coarser spatial resolution or emphasis on hydrological indicators rather than explicitly quantifying exposed population.
• Quantifies the relative contributions of climate-driven flood hazard changes and population redistribution to future flood exposure in the Yangtze River Basin through a dedicated decomposition analysis.
• Evaluates regional exposure trajectories not only in conventional time slices but also at discrete global warming levels (1.5 °C to 4.5 °C), directly linking regional impacts to international climate policy targets.
• Identifies the middle and lower Yangtze as persistent hotspots across scenarios, time slices, and warming levels, highlighting them as priority regions for spatially targeted adaptation and risk-informed development.

Funding

• National Natural Science Foundation of China (52388101)
• Guangdong Basic and Applied Basic Research Foundation (2025A1515510001)
• National Key Research and Development Program of China (2024YFF0808803)

Citation

@article{Qi2026Climate,
  author = {Qi, Wei and Lu, Libin and Cai, Yanpeng and Tan, Qian},
  title = {Climate change overrides population dynamics in driving flood exposure in the Yangtze River Basin},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2026.103418},
  url = {https://doi.org/10.1016/j.ejrh.2026.103418}
}