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. Heat waves are becoming more frequent, more intense, and longer. Specifically, between 1980 and 2022, the duration of conventional, atmospheric heat waves has increased to an average of four days. In addition to duration, heat waves have two other relevant dimensions: their intensity and frequency. In principle, the key cause of the worsening of heat waves in rivers would be the same as in the atmosphere: climate change.