Why most rivers don't respond to storms the same way twice
The same amount of rain falling on the same landscape at different times can send very different amounts of water into its rivers, according to a new study in Nature Water. The research offers a global picture of how catchments behave—not where rivers are or how much water they carry, but how consistently landscapes turn rainfall into river flow.
This study, published in Nature Water, reveals that rainfall on the same landscape can produce vastly different amounts of water in rivers depending on the catchment. A catchment is a land area that drains water into a river. The research, led by hydrologist Dr. Ali Ameli from the University of British Columbia, classifies catchments into three categories: simple, intermediate, and complex.
Simple catchments, found in just 1.5% of the land, behave consistently, delivering roughly the same amount of water to rivers each time a given amount of rain falls. Complex catchments, covering 87% of the land, have catchments that behave differently each time similar amounts of rain fall. Intermediate catchments, the remaining 1.5%, switch between behaving like simple and complex catchments.
The study found that the frequency and rhythm of rainfall are the strongest factors distinguishing simple and complex catchments. Persistent rainfall leads to more consistent catchment behavior, while frequently alternating wet and dry conditions cause catchments to behave differently each storm. Drier regions, with less water available after evaporation and plant use, tend to have complex catchments, while wetter regions with simpler behavior are found in humid areas.
This global classification provides hydrologists a common framework to compare catchments worldwide and model their behavior accurately.
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