Climate change paradox: worsening droughts amidst increasing average precipitation across South Korea

• Droughts intensified despite increased precipitation over 109 years in South Korea. • Bootstrap analysis shows rising climate variability and worsening extreme droughts. • Streamflow strongly correlates with SPEI in ten major dam basins, especially long time scales. • SPEI outperforms SPI in capturing long-term droughts influenced by temperature. This study assesses century-long changes in drought trends and the potential implications of climate change for water resources across South Korea. We investigate these trends by analysing precipitation and temperature data from six weather stations with long records and examine their relationship with streamflow from the catchments of South Korea’s ten largest dams. Given the global rise in temperature, which is likely to impact precipitation and alter water availability, we aim to investigate how drought patterns have evolved and their potential implications for water resources. We use t-tests and bootstrap analyses to evaluate temporal changes in both average and extreme rainfall and evaporation accumulations over periods ranging from three months to five years, using the Standardized Precipitation Evaporation Index (SPEI). Additionally, we assess the implications of these changes for water resources by comparing them with shifts in the Standardized Streamflow Index (SSI) for recent decades where streamflow data are more available. Our findings reveal an exacerbation of droughts, especially when longer time-step data are considered, across most regions of South Korea (35 of 42 cases) following an increase in meteorological variability (34 of 42 cases). This occurs despite an increase in average precipitation levels (+14.9–+28.6 mm/decade). Furthermore, a strong correlation is confirmed between SPEI and SSI in the catchments of ten major dam (r > 0.79 across all cases), demonstrating meteorological conditions are closely linked with hydrological states. This paradoxical outcome, driven by changes in meteorological variability, indicates a reduction in the reliability and/or volume of water supply, underscoring the urgent need to develop adaptive strategies in response to evolving climate dynamics.