Impact du changement climatique sur le cycle de l'eau
2023-07-26
Chercheur Ala'a Yassieen Mohammed
Maîtrise en télédétection - Université de Bagdad
Le cycle de l'eau dans la nature ou le cycle hydrologique est défini comme le cycle responsable du mouvement de l'eau dans le système atmosphérique de la Terre, et il est représenté dans de nombreux processus (tels que l'évaporation, la transpiration, la condensation, les précipitations, l'écoulement ... et d'autres), où à travers ce cycle, l'eau est recyclée pour maintenir la présence de masses d'eau, la continuité de la condensation des nuages et les précipitations au fil du temps.
Le changement climatique fait référence aux changements à long terme de la température et des schémas météorologiques. Ces changements peuvent être naturels, dus à des variations de l'activité solaire ou à de grandes éruptions volcaniques. Mais depuis le dix-neuvième siècle, les activités humaines ont été le principal moteur du changement climatique, principalement en raison de la combustion de combustibles fossiles tels que le charbon, le pétrole et le gaz.
(Image montrant le cycle de l'eau dans la nature)
The phenomenon of climate disruption is explained by a number of scientists in the warming of the oceans and atmosphere at the global level and over many years. Most of the studies carried out in this regard are due to the phenomenon of climate change due to a number of factors, most notably industrial activity and the toxic gases that accumulate in the atmosphere, the effects of climate change on the water cycle are profound and have been described as the overall intensification or strengthening of the water cycle (also called the hydrological cycle). This effect has been observed since at least 1980. One example is the intensification of heavy precipitation events. This has important side effects on the availability of freshwater resources, as well as other water reservoirs such as oceans, ice sheets, atmosphere and the Earth's surface. The water cycle is essential for life on Earth and plays a huge role in the global climate and ocean circulation. Warming of the earth is expected to lead to changes in the water cycle for various reasons. For example, a warmer atmosphere could contain more water vapor that has effects on evaporation and precipitation. The oceans also play a big role, absorbing 93% of heat. The increase in ocean enthalpy since 1971 has had a significant impact on the ocean as well as on the cycle. To avoid further changes, or more extremes, in the water cycle, greenhouse gas emissions must be reduced.
The main reason for the intensification of the water cycle is the increase in the amount of greenhouse gases, which leads to a warmer atmosphere through global warming. Physics suggests that saturation vapor pressure increases by 7% when the temperature rises by 1 °C (as shown by the Clausius and Clapeyron equation). The strength of the water cycle and its changes over time are of great importance, especially with climate change. The essence of the overall hydrological cycle is the evaporation of moisture in one place and precipitation in others. In particular, evaporation exceeds rainfall over the oceans, allowing moisture to be transported by the atmosphere to Earth where rainfall exceeds evaporation, and runoff flows into streams and rivers and flows into the ocean, completing the cycle. The water cycle is an essential part of the energy cycle through evaporative cooling on the surface and latent heating of the atmosphere, where atmospheric systems play an essential role in moving heat up. If water is available, the excess heat often goes to evaporation, as always happens in the oceans, otherwise it goes to overheating. The availability of water as well as the atmosphere's ability to retain water, which increases proportionally with increasing temperature, means that water plays a major role on oceans and tropics, but much less on continents and polar regions. This is why rising temperatures dominate the Arctic and on land. Many water cycle properties have the potential to cause sudden (abrupt) changes in the water cycle. However, the likelihood of such changes occurring during the twenty-first century is currently considered low. Global warming leads to changes in the global water cycle. They include, first of all, an increase in atmospheric water vapor pressure. This causes changes in rainfall patterns in terms of frequency and intensity, as well as changes in groundwater and soil moisture combined. These changes are often referred to as intensifying and accelerating the water cycle The main processes that will also be affected are droughts, floods, tropical cyclones, glaciers, snow cover and extreme weather events. These changes are often referred to as intensifying and accelerating the water cycle The main processes that will also be affected are droughts, floods, tropical cyclones, glaciers, snow cover and extreme weather events. Climatic models do not mimic the water cycle well. One reason is that precipitation is a difficult amount to handle because it is intermittent in nature. Often, only the average quantity is taken into account. People tend to use the term precipitation as if it were the same as the amount of precipitation. What actually matters when describing changes in rainfall patterns on Earth is more than just the total amount: it also concerns intensity (how intense it rains or snowfalls), frequency (how often), duration, and type (rain or snow).
La cause la plus importante peut être identifiée comme des précipitations intermittentes. L'augmentation de la quantité de gaz à effet de serre provoque une élévation de la température de l'air. La pression de vapeur de saturation de l'air augmente avec l'augmentation de la température, ce qui signifie que l'air plus chaud peut contenir plus de vapeur d'eau. Comme l'air peut contenir plus d'humidité, l'évaporation est favorisée. La relation entre la température et la pression de vapeur de saturation est décrite dans l'équation de Clausius–Claperon, qui stipule que la pression de saturation augmentera de 7 % lorsque la température augmentera de 1 °C. Cela est évident dans les mesures de vapeur d'eau dans la troposphère, qui sont fournies par des satellites, des sondes radio et des stations de surface. Le cinquième rapport d'évaluation du Groupe d'experts intergouvernemental sur l'évolution du climat a conclu que la vapeur d'eau dans la troposphère a augmenté de 3,5 % au cours des 40 dernières années, ce qui est cohérent avec l'augmentation de température observée de 0,5 °C.
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