Freshwater and climate change
Freshwater refers to water with low concentrations of dissolved salts, essential for human life and the environment. While 97.2% of Earth's water is seawater, most freshwater is found in glaciers and groundwater, with surface water—such as lakes and rivers—being the most accessible for human use. This surface water supports agriculture, industry, and municipal needs, highlighting its critical role in modern societies. Climate change poses significant threats to freshwater resources, causing uncertain impacts through increased evaporation and altered precipitation patterns. Notably, melting glaciers and changing weather patterns can lead to both flooding and reduced water supply, particularly affecting rivers and streams that rely on glacial melt. As climate change exacerbates water stress, particularly in vulnerable regions, over 2 billion people currently lack access to safe drinking water, with projections indicating that nearly half the global population could face severe water stress by 2030. Consequently, effective policy integration and community efforts are essential to conserve freshwater resources, reduce greenhouse gas emissions, and ensure sustainable access for future generations.
Freshwater and climate change
Freshwater is essential to support human life and Earth’s biodiversity. Freshwater resources are under pressure from climate change and other sources, so policy makers must understand how climate affects freshwater and the importance of water resources.
Background
Freshwater is water that contains low concentrations of dissolved solids, such as salts. Water containing less than 1 gram per liter of dissolved solids is considered fresh, whereas water containing more than 1 gram per liter of such solids is saline. Ocean water has a salinity of approximately 35,000 parts per million. Some 97.2 percent of the total volume of the Earth’s water is seawater. The majority of the Earth’s freshwater is sequestered in glaciers. More than 98 percent of available freshwater is groundwater, and less than 2 percent of available freshwater is in lakes, running water, and wetlands.
Freshwater and the Hydrologic Cycle
Freshwater storage and migration are essential components of the Earth’s hydrologic cycle. The ocean receives less water through precipitation than it loses through evaporation. Earth’s land surface receives more water through precipitation than it loses through evapotranspiration. Surface runoff and base flow of freshwater from the land surface to the ocean are critical to maintain the balance of the hydrologic cycle, preserving sea levels and preventing permanent surface flooding.
Human Reliance on Surface Water
Even though most freshwater exists as groundwater and glacier ice, surface water—such as running water and lakes—is more important to human life, because it is readily accessible. In ancient cultures, fresh surface water was mainly used as drinking water. With the development of civilization, more and more surface water was used for irrigation and industry. Water usage in modern society varies among nations. Water resources in developing countries are mainly employed for irrigation and municipal uses. On the other hand, developed countries use most of their water for industry.
Water use by households, businesses, and communities is classified as municipal water use. Basic municipal water use includes drinking, washing, bathing, cooking, and sanitation. In addition, municipal water is used—especially in developed nations—for swimming pools, recreational parks, firefighting, street and car washing, and gardening. The largest use of surface water worldwide is for agriculture. Because of the increasing demand for water to grow crops, most of agricultural water use is for irrigation, or the controlled application of water to foster crop growth. As the human population grows, greater quantities and more efficient use of freshwater is necessary to meet the increasing demand for food. In addition, since the Industrial Revolution water has been used to drive almost every aspect of industry, including mining, automobile and other manufacturing, and energy production.
Impact of Climate Change on Rivers, Streams, and Lakes
Any climate change, and particularly global warming, will have a significant impact on the Earth’s freshwater supply. However, the precise effect of increasing temperatures on the water supply is uncertain. Higher air temperatures can generate more precipitation, but they also increase evaporation. More precipitation and improved plant water-use efficiency due to increased atmospheric carbon dioxide (CO2) would increase water supply. However, more precipitation and warmer temperatures could potentially extend the growing season of plants, which could result in greater transpiration and reduce water supply. The net effect of increasing temperature on water supply is thus unclear, especially on a global scale.
Studies have revealed other potential sources of dramatic climate-change-related impact on surface freshwater. Shrinking alpine glaciers would significantly reduce water supplies for many rivers and streams that originate from melting snow and glaciers while simultaneously releasing excess floods of water into glacial lakes. Even the world’s largest freshwater lake, Lake Baikal, responds strongly to the Earth’s warming temperature. Melting glaciers, extreme rainfall, changes in snowfall, increasing droughts, and rising water levels are examples of tangible ways climate change may affect Earth's freshwater supply.
Context
The availability of surface water varies among continents and countries. In 2022, more than 2 billion people lacked access to safe drinking water at home. Approximately two-thirds of the world’s population will be living in water-stressed areas by 2025 if no serious actions are taken to control climate change, water pollution, and water usage. By 2030, almost half of the global population could be living under severe water stress if no action is taken. Climate change has a significant impact on surface water resources. Globally, many policies have been established to reduce greenhouse gas emissions and promote the usage of renewable or alternative energy. However, a significant amount of water has been used to produce energy, and energy has been increasingly used to process water. With the pressure of population growth and limited energy and water resources, all governments and communities need to work together to develop a plan to integrate water and energy policy making. Communities and individuals need to conserve water and energy resources, and they must control pollution and mitigate climate change to ensure safe access to freshwater in the future.
Key Concepts
base flow: the portion of stream flow that comes from groundwaterdrainage basin: an area bounded by a continuous and topographically higher divide where water from precipitation drains downhill into a body of waterevaporation: the process by which water changes from liquid to vaporevapotranspiration: the sum of evaporation and transpirationgroundwater: water stored beneath the land’s surfacehydrologic cycle: the continuous circulation of solid, liquid, and gaseous water among the oceans, atmosphere, and continentsprecipitation: the condensation of atmospheric water vapor that deposits hail, mist, rain, sleet, or snow on the Earth’s surfacesurface runoff: water from precipitation that flows over land surfaces to bodies of watersurface water: water found on land in such bodies as ponds, lakes, streams, rivers, wetlands, and inland seastranspiration: the process through which water evaporates from the aerial parts of plants, especially leaves
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