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Concept
Effects of climate change on the water cycle
Résumé
The effects of climate change on the water cycle are profound and have been described as an intensification or a strengthening of the water cycle (also called hydrologic cycle). This effect has been observed since at least 1980. One example is the intensification of heavy precipitation events. This has important negative effects on the availability of freshwater resources, as well as other water reservoirs such as oceans, ice sheets, atmosphere and land surface. The water cycle is essential to life on Earth and plays a large role in the global climate and the ocean circulation. The warming of our planet is expected to cause changes in the water cycle for various reasons. For example, warmer atmosphere can contain more water vapor which has effects on evaporation and rainfall.
The underlying cause of the intensifying water cycle is the increased amount of greenhouse gases, which lead to a warmer atmosphere through the greenhouse effect. Physics dictates that saturation vapor pressure increases by 7% when temperature rises by 1 °C (as described in the Clausius-Clapeyron equation).
The strength of the water cycle and its changes over time are of considerable interest, especially as the climate changes. The essence of the overall hydrological cycle is the evaporation of moisture in one place and the precipitation in other places. In particular, evaporation exceeds precipitation over the oceans, which allows moisture to be transported by the atmosphere from the oceans onto land where precipitation exceeds evapotranspiration, and the runoff flows into streams and rivers and discharges into the ocean, completing the cycle. The water cycle is a key part of Earth's energy cycle through the evaporative cooling at the surface which provides latent heat to the atmosphere, as atmospheric systems play a primary role in moving heat upward.
If water is available, extra heat goes mostly into evaporation, as it always does on the oceans, otherwise it goes into raising air temperature.
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