環境：世界の河川の半数以上では流水が途絶える日がある

More than half of the world’s rivers cease to flow for at least one day per year, suggests a paper published in Nature. The findings indicate that flow intermittency is more common than previously thought, which may necessitate changes in river-management strategies.

Most river courses include rivers or streams that will periodically cease to flow, and these are expected to increase in the coming decades due to changing climates or human activity. However, the full global extent of intermittent (non-perennial) rivers is unknown, which means they can be overlooked when developing river-management strategies.

Mathis Messager and colleagues developed a model to predict the extent of non-perennial rivers globally, which was applied to the RiverATLAS database, representing 23.3 million kilometres of the global river network. They predict that between 51% and 60% of rivers and streams by length cease to flow for at least one day a year, indicating that non-perennial rivers are the most widespread river type. They also estimate that for 52% of the world’s population the closest river or stream is non-perennial. The authors indicate that climatic variables are important predictors of which rivers may be intermittent. They suggest that 95% of rivers found in extremely hot and dry areas — such as northern Australia, parts of India, and the Sahel region of Africa — are prone to flow cessation. In colder climates, interrupted river flow is often due to ice or storage of precipitation as snow.

The authors conclude that flow intermittence should be included in river models to ensure effective river-management strategies that protect the biodiversity and ecosystems of non-perennial rivers.