Park et al. (2025) Climate change paradox: worsening droughts amidst increasing average precipitation across South Korea

Identification

• Journal: Journal of Hydrology
• Year: 2025
• Date: 2025-11-24
• Authors: S. B. Park, Andrew W. Western, Murray Peel
• DOI: 10.1016/j.jhydrol.2025.134658

Research Groups

• Department of Infrastructure Engineering, The University of Melbourne, Australia
• Korean Water Resources Corporation (K-water), the Republic of Korea

Short Summary

This study reveals a climate change paradox in South Korea, demonstrating that droughts have worsened in frequency and intensity over the past century despite an overall increase in average precipitation, driven by enhanced meteorological variability and temperature-driven evapotranspiration, with strong implications for water resources.

Objective

• To investigate how the occurrence of droughts has changed in South Korea amidst increasing trends in precipitation and temperature.
• To statistically verify historical changes in droughts using robust methods while ensuring data independence.
• To assess how climatic variables can inform drought behavior in water resources, particularly for periods prior to observed streamflow data.

Study Configuration

• Spatial Scale: South Korea (total area of 100,210 km²), focusing on six long-term weather stations (Incheon, Seoul, Gangneung, Mokpo, Daegu, Busan) and the catchments of its ten largest dams.
• Temporal Scale: Century-long analysis of meteorological data (1904/1912–2020), with comparative periods of 1912–1941 and 1991–2020. Dam inflow data periods vary from 23 to 50 years (e.g., 1974–2023). Drought indices were computed for 3, 6, 12, 24, 36, 48, and 60-month accumulation periods.

Methodology and Data

• Models used:
  • Standardized Precipitation Evaporation Index (SPEI)
  • Standardized Precipitation Index (SPI)
  • Standardized Streamflow Index (SSI)
  • Thornthwaite method for Potential Evapotranspiration (PET) estimation.
  • Statistical methods: Welch's t-test, Bootstrap Sampling, Mann–Kendall test, Sen’s slope estimator, Pearson's correlation coefficient.
• Data sources:
  • Monthly precipitation and temperature data from six long-term weather stations (1904/1912–2020) provided by the Korean Meteorological Administration (KMA).
  • Monthly streamflow, precipitation, and temperature data for the catchments of 10 main dams (varying operational periods, e.g., 1974–2023) from the Korean Water Resources Corporation (K-water).
  • Areal average precipitation for dam catchments calculated using a Thiessen Polygon network.
  • Monthly average temperature for dam catchments calculated using a Thiessen network based on 95 operating synoptic stations.

Main Results

• Annual mean temperatures increased across all six stations from +0.10 °C/decade to +0.25 °C/decade (1904–2020), with strongest warming in spring and winter.
• Annual mean precipitation increased across all six stations from +14.9 mm/decade to +28.6 mm/decade (1904–2020), representing +1.1% to +2.3% per decade, with the clearest increases in summer.
• Drought conditions have worsened (35 of 42 cases) and meteorological variability has increased (34 of 42 cases) across most regions and time scales in the recent period (1991–2020) compared to the past (1912–1941), despite the increase in average precipitation.
• Drought frequency more than doubled in Seoul across all time scales, and generally increased at four of six stations. Average drought intensity increased across most time scales at all stations except Gangneung.
• SPEI variability increased, particularly for longer time scales (≥24 months), showing both more extreme wet (higher 90th percentile) and drier (lower 10th percentile) conditions.
• While Welch's t-tests showed no significant difference in mean SPEI between periods, bootstrap analysis confirmed a consistent rise in meteorological variability and worsening drought conditions.
• A high positive correlation (r > 0.79 across all time scales, and >0.85 for ≥12 months) was found between SPEI and SSI in the 10 main dam catchments, indicating SPEI effectively reflects hydrological drought impacts.
• SPEI demonstrated a slightly stronger correlation with SSI than SPI, especially for larger dam catchments, highlighting the importance of temperature-driven evapotranspiration in influencing streamflow.

Contributions

• Provides the first systematic analysis of century-long observational records in South Korea to demonstrate the coexistence of increasing precipitation and worsening droughts.
• Integrates century-long meteorological observations with variability analysis using SPEI, linking these to hydrological conditions (dam inflows) at a national scale.
• Addresses the gap in connecting long-term meteorological drought trends to water resources drought trends, offering insights into pre-observation period hydrological behavior.
• Advances the understanding of the climate change paradox (worsening droughts despite increased precipitation) by demonstrating it at a national scale, building upon previous regional and global findings.
• Offers a critical foundation for applied research and policy discussions on water management strategies in climate-vulnerable regions.

Funding

• Korea Water Resources Corporation (K-water)
• The University of Melbourne (PhD scholarship)

Citation

@article{Park2025Climate,
  author = {Park, S. B. and Western, Andrew W. and Peel, Murray},
  title = {Climate change paradox: worsening droughts amidst increasing average precipitation across South Korea},
  journal = {Journal of Hydrology},
  year = {2025},
  doi = {10.1016/j.jhydrol.2025.134658},
  url = {https://doi.org/10.1016/j.jhydrol.2025.134658}
}