"However, this is beginning to change. By studying the impact of heat waves since 1980 on more than 1,400 rivers, American researchers have discovered that these extreme events are increasing at a rate four times greater than that of atmospheric heat waves. The work, published in the journal PNAS, is based on data from the United States, but European experts believe the phenomenon is global."
"Rivers constantly mix heat through moving water. This mixing smooths out temperature spikes, so rivers don't typically warm as much as the surrounding air, says Li Li, a Pennsylvania State University professor and co-author of the research. But the downside is that once a river warms, the entire system tends to stay warm, prolonging the duration of the heat wave, adds the researcher, head of a laboratory that studies the state of aquatic systems."
"Specifically, between 1980 and 2022, the duration of conventional, atmospheric heat waves has increased to an average of four days. But in rivers, extreme thermal events now last 7.2 days on average. Water has a greater thermal memory than air. This means that once a river warms up, it tends to stay warm for days because the water retains heat."
Temperature measurements from 1,471 freshwater streams in the United States show that river heat waves have been increasing faster and lasting longer than atmospheric heat waves since 1980. Extreme thermal events in rivers now last on average 7.2 days compared with an average of four days for atmospheric heat waves. Rivers mix heat through flowing water, which dampens temperature spikes but gives water greater thermal memory, so warmed waterways remain warm for days. Concurrent warming of large water bodies like oceans is also occurring. European experts consider the pattern likely global, raising concerns about prolonged aquatic and ecosystem heat stress.
Read at english.elpais.com
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