Researchers from the Department of Infrastructure Engineering at the University of Melbourne and the Korean Water Resources Corporation (K-water) set out to answer a troubling question: how can droughts worsen in South Korea when rainfall is increasing? Using more than a century of temperature and precipitation records from six of the country’s oldest weather stations, combined with streamflow data from South Korea’s ten largest dams, the study examines how climate change has reshaped drought patterns and water availability over time. The findings overturn a common assumption that more rain automatically means greater water security.
Warmer, Wetter, Yet More Fragile
The data show clear long-term warming across South Korea. Since the early 1900s, temperatures have risen steadily at all six stations, with especially strong warming in cities such as Seoul and Daegu. At the same time, annual rainfall has increased everywhere by roughly 15 to nearly 30 millimetres per decade. On average, the country is both warmer and wetter than it was a century ago. Yet these averages mask growing instability. Seasonal analysis reveals that most rainfall increases are concentrated in summer, while winters show little change or even slight declines, increasing the risk of dry periods outside the monsoon season.
Why Droughts Are Getting Worse
To understand drought more accurately, the researchers used the Standardized Precipitation Evapotranspiration Index, or SPEI. Unlike rainfall-only measures, SPEI accounts for temperature-driven evaporation, which is increasingly important in a warming climate. The results show that droughts have become more frequent and more intense in recent decades, particularly when measured over longer periods of one to five years. These long-term droughts matter most for rivers, reservoirs, and water supply systems.
Short-term droughts still fluctuate widely from year to year, but long-term drought patterns now show deeper and longer-lasting dry conditions than those observed in the early 20th century. In several major cities, including Seoul, drought frequency has more than doubled at some time scales. This worsening occurs even though total rainfall has increased.
The Hidden Role of Climate Variability
One of the study’s most important insights is that the problem is not declining average rainfall, but rising climate variability. Statistical tests show little difference in average drought conditions between the early and recent periods. However, when the researchers examine extremes, a clear shift emerges. Wet periods have become wetter, but dry periods have also become drier. The gap between these extremes has widened sharply, especially over longer time scales.
This growing variability is driven by two forces. Rainfall has become more uneven, with stronger swings between wet and dry years, while rising temperatures have increased evaporation, pulling moisture out of soils, rivers, and reservoirs faster than before. Much of the extra rainfall is therefore lost, reducing its benefit for long-term water storage. In simple terms, South Korea is receiving more rain but keeping less usable water.
What This Means for Water Security
The study confirms that these worsening drought patterns directly affect water resources. Across all ten major dam catchments, the researchers found very strong links between meteorological drought and reduced streamflow, especially at time scales longer than one year. This means that changes in climate variability are already translating into lower and less reliable river flows. Drought indices that include temperature effects perform better at explaining these changes than rainfall-only measures, highlighting the growing role of heat in shaping water shortages.
The findings carry a clear warning. Water management strategies based on historical averages are no longer sufficient in a warming world. Even countries experiencing more rainfall may face higher drought risk if climate variability increases. For South Korea, where population density is high and water demand is intense, the results point to an urgent need to rethink drought planning, reservoir management, and climate adaptation strategies. The paradox revealed by this study, that more rain can coincide with worse droughts, offers a lesson with global relevance as climate change reshapes water systems worldwide.