More flow upstream and less flow downstream: The changing form and function of global rivers

Area of Science:

• Hydrology
• Environmental Science
• Geospatial Analysis

Background:

• Global river systems are crucial for ecosystems and human activities.
• Understanding recent changes in streamflow is essential for water resource management and ecological health.
• Previous studies often lacked the scale to capture fine-grained changes in river networks.

Purpose of the Study:

• To map and assess recent changes in daily streamflow across millions of global rivers from 1984 to 2018.
• To identify spatial patterns of streamflow alteration, particularly shifts between river headwaters and outlets.
• To quantify the impacts of these changes on erosion, flood frequency, and nutrient dynamics.

Main Methods:

• Utilized a "detail at scale" approach by mapping daily streamflow for approximately 2.9 million rivers.
• Analyzed streamflow data from 1984 to 2018 to detect significant increases and decreases.
• Assessed changes in stream power, 100-year flood frequency, and seasonal flow regimes.

Main Results:

• River outlets predominantly showed significant decreases in streamflow.
• Headwaters were 1.7 times more likely to exhibit significant streamflow increases than decreases.
• Approximately 29% of the global land surface experienced an upstream shift in streamflow.
• Smallest streams showed the most pronounced changes, including a 5% increase in erosion potential and a 42% increase in 100-year flood frequency.

Conclusions:

• Recent global streamflow changes exhibit a significant upstream shift, altering hydrological dynamics.
• These alterations pose increased risks of erosion and flooding, especially in smaller river systems.
• The "detail at scale" mapping approach provides unprecedented insights into hydrosphere changes and can be widely adopted for future research.