Earth's Rivers Are Drying Up...Last Year's River Flow Hit 35-Year Low [Reading Science]

WMO Releases Global Water Resources Status

Glaciers Shrink for Four Consecutive Years, Droughts and Floods Occur Simultaneously

The Earth's rivers have recorded their driest state in the past 35 years. While river discharge is decreasing in many parts of the world, other regions have been hit by major floods. Reservoirs that have supplied water during droughts—such as glaciers and groundwater—are also diminishing. This is a warning that the water cycle is changing not only to simply bring about water shortages, but to disrupt the timing and locations where water is supplied when and where it’s most needed.

According to the "World Water Resources Status Report 2025" released by the World Meteorological Organization (WMO) on September 17, global river discharge last year reached its lowest level in the past 35 years. Over 36% of the world’s watershed areas had lower than average discharge, and only about one-third of global rivers recorded discharge within the normal range. This is significantly lower than the 30-year average of 46%.

On the 11th of last month, a ship was passing along the exposed riverbed next to the lowered water level of the Rhine River in Düsseldorf, Germany. Photo by Hesham Elsherif/Anadolu Agency

Rivers Are Drying Up, Glaciers Are Shrinking...Even Water Reservoirs Are Shaking

The report diagnosed that river discharge below the normal range has become prominent over the past seven years. The total land water storage—including snow, glaciers, soil moisture, and groundwater—also showed a decreasing trend after 2014–2016. In major glacier regions worldwide, there have been four consecutive years of net ice loss. Last year, the estimated glacier loss totaled approximately 408 billion tons.

However, the entire Earth is not drying up in the same way. About 21% of watersheds globally saw higher than average discharge. In South Asia and Southeast Asia, major floods occurred as monsoon rains overlapped with tropical cyclones. Hwang Seokhwan, Research Fellow at the Water Resources and River Research Center of the Korea Institute of Civil Engineering and Building Technology, explained, "It is more accurate to say that what’s changing is how and where rainfall and river water are concentrated by region and season, rather than a reduction in the planet’s total water volume."

This contrast was also evident in Australia. Claire Stephens, Lecturer in Environmental Science at the University of New South Wales, noted that last year, dry winter weather in western and southern Australia dried out soils and damaged crops and vegetation; meanwhile, the north experienced repeated major floods. She evaluated, "This report shows the growing year-to-year variability in the water cycle." However, she added that the report did not specifically attribute the causes of individual disasters to climate change.

The reduction in glaciers is connected not just to immediate disaster risk but also long-term water shortages. When glaciers first begin melting, the flow of water into rivers may increase, but as glaciers themselves shrink, summer water supplies could diminish in the future. Research Fellow Hwang pointed out that in some regions such as the Caucasus and the Alps, the outflow from glacier melt may have already passed its peak.

However, it is difficult to confirm a long-term trend based only on changes in river discharge over the past 7 to 10 years. This is because natural fluctuations caused by El Niño and La Niña, climate change, and excessive groundwater extraction all have different impacts.

World River Flow Distribution Map. The 2024 global river flow distribution published by the World Meteorological Organization (WMO). Orange indicates areas with below-average flow, while turquoise indicates areas with above-average flow. At the time of analysis, 35% of areas showed flow within the normal range. Provided by the WMO, World Water Resources Report 2024.

Even When It Rains, Usable Water May Decrease...Korea Also Needs to Change Its Management Approach

In Spain, even regions that have traditionally seen frequent rainfall are becoming vulnerable to drought. Jorge Olcina, Professor of Regional Geographic Analysis at the University of Alicante, explained, "In areas where rain has usually been regular, even a reduction in rainfall for just two or three months can cause problems for agricultural and urban water supply." He emphasized that regions with various sources of water—such as rivers, groundwater, seawater desalination, and wastewater reuse—are comparatively better able to respond to rainfall shortages.

This suggests that Korea should not judge water shortage risks based solely on precipitation levels. Higher temperatures lead to increased evaporation, and during droughts, dry soil absorbs rainwater first. When snow accumulation in winter is low, the water supplied to rivers in spring can also decrease.

Jeong Soo-jong, Professor at the Graduate School of Environmental Studies at Seoul National University, said, "With ongoing warming, even if precipitation remains at current levels, the actual amount of usable water could decrease," adding, "Korea’s water resources planning and climate risk assessments should shift from relying only on precipitation forecasts to using hydrological indicators such as river discharge, soil moisture, and reservoir water levels."

As Korea faces both intense summer downpours and droughts during dry periods, securing industrial water is also a challenge. Research Fellow Hwang noted that more facilities, such as semiconductor factories and data centers, are being established where water use cannot be easily reduced even during droughts. He recommended that instead of relying on a single water source, alternative sources such as wastewater reuse should be secured, and a system for distributing costs should be put in place.

The problem is that areas most affected by water disasters tend to lack observational data. In the last five years, more than 80% of deaths from water-related disasters occurred in Asia and Africa, but only about 7% of observation stations included in this report's discharge data were located in those two regions. Experts emphasized the need to expand local observation networks and to increase data sharing between countries.

This content was produced with the assistance of AI translation services.