Land and seas are connected in a continuous cycle of water; the sun warms the surface of the ocean, creating atmospheric humidity through evaporation. The warm, humid air is transported towards the land by the wind, and when it encounters cold layers of air it rises above them. At altitude, the air cools and the moisture condenses, forming clouds. When precipitation feeds streams and rivers and these flow into the sea, the cycle is completed. This cycle is the foundation of life on land, but it is vulnerable; according to the sixth report by IPCC (Intergovernmental Panel on Climate Change), published in 2021, human activities interfere with the hydrologic cycle. More precisely, it is the change in land use and thus vegetation, the extraction of water from the ground or rivers and the emission of aerosols and carbon dioxide that have an impact. These factors are interconnected, for example if the land cover is changed due to agricultural activities, this also changes the soil’s capacity to soak up surface water, as well the possibility of evaporation. Decreased uptake of water can lead to flooding and depleted groundwater, further exacerbated by the extraction of water for irrigation. At the same time, the dry soil can evaporate less water but heat up more, which has an influence on cloud development. This water cycle is also linked to the carbon cycle, as a higher availability of carbon dioxide in the atmosphere increases the efficiency of plants at retaining water. In order to adapt to these conditions in times of global climate change, measures like sustainable irrigation and reforestation are critical.
Sources: Douville, H. et al., “Water Cycle Changes”, Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, ed. V. Masson-Delmotte et al., (2021): 1055–1210.