Reflection of a snowy mountain in the water of a lake against a blue sky

What is the hydrological cycle?

The hydrological cycle describes the circulation of water from the ocean and other water surfaces to the atmosphere and land.

Evaporation from the oceans is an important source of water vapour in the atmosphere. Precipitation, rain, snow, sleet or freezing rain falls from clouds and is a loss of atmospheric water, as it removes water from the atmosphere.

Precipitation brings water to the earth's surface and provides a source of water for the soil. On land, precipitation can collect in lakes, flow in rivers to the ocean or percolate into the soil.

An interaction between the soil and the atmosphere

The hydrological cycle is an interactive system. Water in the atmosphere, in the ocean, on land and in the subsoil is linked, and changes in any one of them affect the others. Global warming This is why it is so important to monitor the water cycle, because as temperatures rise, evapotranspiration increases, resulting in more water vapour in the atmosphere and less on the ground.

As water plays a major role in weather and climate, it is important to understand the hydrological cycle. A change in one component of the hydrological cycle can have an impact on the weather. For example, a decrease in daytime cloud cover over land will allow more of the sun's energy to warm the ground and atmosphere above by reaching the surface.

Another example is the increase in the frequency of intense rainfall in land areas, which can lead to flooding rather than water infiltration into aquifers.

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The hydrological cycle: regional aspects to consider

Although the hydrological cycle is a global phenomenon, some regional aspects have an impact on France, as hydrological changes in the 6 river basins (Rhone-Mediterranean-Corsica, Rhine-Meuse, Loire-Brittany, Seine-Normandy, Adour-Garonne and Artois-Picardy) have an impact on water supply.

With climate change underway (which is being blamed by the IPCC), changes in rainfall patterns can impact on water management practices by altering water resources. A decrease in precipitation in a catchment will reduce the amount of surface water and therefore percolation into the soil.

Similarly, due to the cyclical nature of water, groundwater removal may reduce the amount of surface water in lakes and rivers. Groundwater recharge, water filtration and flood prevention practices may need to adapt to the regional climate change we are seeing. These adaptations need to consider the water cycle as an interactive system and not as an isolated event.

Climate change and me! | Clip 4: The hydrological cycle