Analyse von Daten von fast 1.500 Standorten in den zusammenhängenden Vereinigten Staaten zwischen 1980 und 2022 ergab, dass Hitzewellen in Flüssen schneller beschleunigen als fast doppelt so lange wie lange Luftwärmewellen

As anyone who lives near one knows well, when the heat hits, rivers serve as a climatic refuge. 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. The impact of these heat waves does not remain limited to the river.

Heat waves are becoming more frequent, more intense, and longer. At the same time, scientists are confirming that climate change is warming large bodies of water, such as the oceans. But what happens to rivers during a heat wave? In principle these waterways, fed by melting ice or underground inflows, buffer the temperature of their immediate surroundings. Even in the current context of global warming, they are portrayed as climate islands or refuges. But the data contradict these assumptions.

“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. This is the first result they have obtained from temperature measurements of 1,471 freshwater streams in the United States.

https://www.pnas.org/doi/10.1073/pnas.2503160122