Climate change is not only affecting global temperatures, it is also fundamentally changing how our waters work. The global water cycle has been intensifying since at least the 1980s, bringing with it intensified cycles of precipitation and evaporation. These changes threaten not only the ecosystems themselves, but also the key services they provide us, such as is clean drinking water, water for irrigation or the ability of rivers to dilute wastewater. The impacts of climate change on the aquatic environment are complex and affect several key areas.<\/p>\n
Warming waters and changes in stratification<\/strong><\/p>\n Due to global warming, water temperatures are rising rapidly. Median river temperatures are expected to rise by 1.3\u00b0C to 3.8\u00b0C by the end of the century<\/strong>. A similar trend is seen for lakes, which are warming globally by a median of 2.5\u00b0C (with possible extremes of up to 5.5\u00b0C), with about a quarter of them losing their seasonal ice cover completely by the end of the century. At the same time, annual evaporation is projected to increase by 16 %, which will directly affect lake levels and total area.<\/p>\n Higher temperatures reduce the solubility of oxygen and directly stimulate the respiration of aquatic organisms. Warming leads to stronger and longer stratification (temperature stratification) of waters in lakes and coastal areas<\/strong>, which isolates the lower layers from the atmosphere and contributes to oxygen depletion. This shift alters established seasonality, resulting in mismatches between predators and their prey. In the seas, intense heat waves massively reduce key communities such as macroalgae and seagrasses.<\/p>\n Extremes in hydromorphology: From drought to flash floods<\/strong><\/p>\n Changing precipitation patterns, coupled with lower snow cover and retention, are radically reshaping river flow regimes. In Europe, this means extremes at both ends of the spectrum: while the north faces more frequent and devastating floods, the south is experiencing increasing intensity of hydrological droughts. These fluctuations damage biological communities by scouring the riverbed during floods or, conversely, by drying out during droughts.<\/p>\n Smaller water bodies, which are critical for maintaining regional biodiversity, are most at risk from drying out and groundwater depletion. Increased river water inflow and sediment transport have brought the phenomenon of so-called coastal darkening<\/strong>, which reduces the depth of light penetration and causes the retreat of macroalgae in favor of animal species.<\/p>\n Geochemical changes and water quality deterioration<\/strong><\/p>\n Extreme weather events directly modify the chemistry of our waters. For example, it is estimated that Nitrogen mineralization from soil can increase by more than 30% after rewetting.<\/strong>. Reduced river flows mean less dilution of pollution from agriculture and urban wastewater, while extreme summer storms can quickly release massive bursts of nutrients into the water. High evaporation speeds up the salinization of lakes.<\/p>\n Climate change, combined with land use change and the retreat of acid rain, has caused the so-called. browning of lakes (brownification)<\/strong>. In coastal zones, CO2 absorption and local nutrient inputs cause acidification<\/strong>, which makes it impossible for corals, oysters and plankton components to build and maintain their calcareous shells.<\/p>\n Rising sea levels and pressure on coastlines<\/strong><\/p>\n It is estimated that global sea levels will rise by 0.63 to 1.01 meters by 2100<\/strong> in the highest emissions scenario. This will lead to saline intrusion deeper into river systems. This creates the dreaded phenomenon \u201e"estuarine squeeze"<\/strong> \u2013 when the freshwater and brackish zone is pushed inland by the rising sea, but due to artificial anthropogenic barriers it has nowhere to move and disappears. Rising sea levels are already pushing submarine meadows into shallower depths in the Mediterranean Sea and threaten to flood many valuable tidal marshes.<\/p>\n Synergistic effects and complex ecosystem responses<\/strong><\/p>\n Water systems rarely respond to a single isolated factor, but rather face devastating combinations of multiple pressures. A key example is toxic cyanobacterial bloom explosion<\/strong>, for which the combination of warmer water and increasing nutrient inputs is the perfect catalyst. The complex nature of these risks has been tragically demonstrated on the Oder River in 2022<\/strong>. Extreme drought and high temperatures reduced flow, increasing the concentration of existing industrial salt and nutrient pollution. This cocktail created ideal conditions for the massive growth of invasive brackish algae (Prymnesium parvum<\/em>), whose toxins subsequently killed fish along hundreds of kilometers of the river.<\/p>\n Understanding how climate change multiplies the effects of existing pollution and physical modifications is crucial for protecting our water resources and future ecosystem services in a rapidly changing world. JRi&CO2AI\u00a0<\/strong><\/em><\/p>\n