One of the best ways to escape the heat on a summer day is to take a dip in the river to keep you cool. But during the rain, everything happens the other way around: the water in the river seems to become warmer than in clear weather.
"Warming" of water in a river during rain is an apparent phenomenon. If you arm yourself with a thermometer and measure the temperature of the water before and during the rain, it will not be possible to reveal a significant difference.
Warming illusion
The water in the river during the rain seems warmer, not because it really becomes so, but in comparison with the air temperature. The rain is always accompanied by a cold snap. This happens for several reasons.
Very often, a cold atmospheric front comes along with the rain. The rain can be accompanied by wind. Objectively, the wind does not lower the air temperature, but affects its perception by a person, carrying away the layer of air heated from the human body.
Raindrops occur at a fairly high altitude, where the air temperature is much lower than at the Earth's surface, so the temperature of the rainwater is also low. When they reach the ground, raindrops do not have time to heat up to such an extent that their temperature is comparable to that of the air, so they cool the air.
The action of any of these factors is sufficient to cool the air to such an extent that, in comparison with it, the river water seems warmer.
Why does water keep temperature
When it rains, the air cools, but not the water. This is due to the high heat capacity of water. Heat capacity is a physical quantity that expresses the ratio of the heat received by the body and changes in its temperature. On this basis, water in nature is not a "champion", but one of the "champions" among various substances. It is inferior in heat capacity only to ammonia and hydrogen.
Such a high heat capacity, which scientists even call anomalous, is explained by the special structure of water. It consists of triatomic H2O molecules, but only a small part of such molecules in liquid water is in a free state. Most of them are combined into associates - crystal-like structures of several molecules. When water is heated, the hydrogen bonds in the associates are broken. This process requires a lot of energy, so it is not easy to heat water, but it will give off heat just as slowly.
The retention of the water temperature in rivers during rain is just one of the manifestations of the high heat capacity of water. It is this property that allows water to protect the Earth from catastrophic temperature changes that could destroy all living things.
