The multiple arches of the Pont du Gard in Roman Gaul (modern-day southern France). The upper tier encloses an aqueduct that carried water to Nimes in Roman times; its lower tier was expanded in the 1740s to carry a wide road across the river.
Because Earth's environment is relatively close to water's triple point, water exists on Earth as a solid, a liquid, and a gas. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds consist of suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor.
Map of global water stress (a symptom of water scarcity) in 2019. Water stress is the ratio of water use relative to water availability and is therefore a demand-driven scarcity.
Water scarcity (closely related to water stress or water crisis) is the lack of fresh waterresources to meet the standard water demand. There are two type of water scarcity namely physical and economic water scarcity. Physical water scarcity is where there is not enough water to meet all demands, including that needed for ecosystems to function. Arid areas for example Central Asia, West Asia, and North Africa often experience physical water scarcity. Economic water scarcity on the other hand, is the result of lack of investment in infrastructure or technology to draw water from rivers, aquifers, or other water sources. It also results from weak human capacity to meet water demand. Much of Sub-Saharan Africa experiences economic water scarcity.
There is enough freshwater available globally and averaged over the year to meet demand. As such, water scarcity is caused by a mismatch between when and where people need water, and when and where it is available. The main drivers of the increase in global water demand are the increasingworld population, rise in living conditions, changing diets (to more animal products), and expansion of irrigated agriculture. Climate change (including droughts or floods), deforestation, water pollution and wasteful use of water can also cause insufficient water supply. Scarcity varies over time as a result of natural variability in hydrology. These variations in scarcity may also be a function of prevailing economic policy and planning approaches. (Full article...)
An iceberg is a large piece of freshwater ice that has broken off a glacier or an ice shelf and is floating freely in the open sea. Because the sea around this iceberg is so calm, the underwater portion is visible through the clear water. The largest iceberg ever detected was B-15, which split from the Ross Ice Shelf in Antarctica in 2000, and had a flat top; it had a surface area of 11,000 km2 (4,200 sq mi) and broke into several pieces in 2002 and 2003. This picture depicts an irregularly shaped iceberg with a rounded top, calved from a glacier in the Arctic and photographed in the Arctic Ocean north of Svalbard.
The Haditha Dam is an earth-filled dam in Iraq, holding back the waters of the Euphrates to create Lake Qadisiyah. The area around Haditha is very arid, with a hot desert climate; the annual precipitation is about 127 millimetres (5 in), mainly occurring during the winter. This photograph, taken from the International Space Station in November 2015, shows the reservoir at a low water level, surrounded by an expanse of dry lakebed; the Haditha Dam is visible near the top of the image. Lake Qadisiyah has a maximum water-storage capacity of 8.3 cubic kilometres (2.0 cu mi) and a maximum surface area of 500 square kilometres (190 sq mi). The associated hydroelectric power station is capable of generating 660 megawatts of electricity, and outlets at the foot of the dam can discharge 3,000 cubic metres (110,000 cu ft) of water per second for irrigation.
A side-by-side comparison of the Aral Sea in 1989 and 2008, showing its severe shrinkage owing to poor water resource management. The Aral Sea was once the fourth-largest lake in the world. However, the rivers that fed it were diverted by Soviet-era irrigation projects. It had shrunk to 10% of its former size by 2007, and is still shrinking. The near-loss of the Aral Sea, which is now in Kazakhstan and Uzbekistan, has been considered one of the planet's most disastrous examples of poor environmental resource management.
Image 8A fire hydrant in Alkmaar, the Netherlands. Fire hydrants are a source of water provided by most metropolitan communities to enable firefighters to tap into the municipal water supply to assist in extinguishing a fire.
An example of guttation, the appearance of drops of xylem sap on the tips or edges of leaves of some vascular plants, on an Equisetum. At night, transpiration usually does not occur because most plants have their stomata closed. When there is a high soil moisture level, water will enter plant roots, because the water potential of the roots is lower than in the soil solution. The water will accumulate in the plant creating a slight root pressure. The root pressure forces some water to exude through special leaf tip or edge structures, hydathodes, forming drops. Guttation is not to be confused with dew, which condenses from the atmosphere onto the plant surface.
An animated image showing the long-term mean monthly precipitation around the world. Precipitation occurs when a local portion of the atmosphere becomes saturated with water vapor and condenses, forming rain drops or ice crystals within a cloud via collision that then fall to the surface, except for virga, which evaporates while in the air.
When a liquid drop impacts the surface of a liquid reservoir it can float, bounce, coalesce with the reservoir, or splash. A floating drop remains on the surface for several seconds. Drop bouncing can occur on perturbed liquid surfaces. If the drop is able to rupture the thin film of gas which separates it from the liquid reservoir, it can coalesce. Additionally, higher Weber number drop impacts produce splashing. In the splashing regime, the impacting drop creates a crater in the fluid surface, followed by a crown around the crater. Finally, a central jet, called the "Rayleigh jet" or "Worthington jet", protrudes from the center of the crater. If the impact energy is high enough, the jet rises to the point where it pinches off, sending one or more droplets upward out of the surface.
The head of an impact sprinkler, a type of irrigation sprinkler in which the sprinkler head, driven in a circular motion by the force of the outgoing water, pivots on a bearing on top of its threaded attachment nut. Invented in 1935 by Orton Englehardt, it quickly found widespread use.
Image 17A view of the Rosoki River in the eponymous village, Macedonia
Morning mist on Lake Mapourika, a lake on the West Coast of New Zealand's South Island. It is the largest of the west coast lakes, a glacier formation from the last ice age. It is filled with fresh rain water which runs through the surrounding forest floor, collecting tannins and giving it its dark colour.
Plate XIX of "Studies among the Snow Crystals ... " by Wilson Bentley (1902), the first person known to photograph snowflakes. He did so by catching an individual snowflake on a blackboard, rushing it onto some black velvet, which he would then photograph using a bellows camera he had attached to a microscope. His first photograph of a snowflake was on January 15, 1885 and he would capture over 5000 images of crystals in his lifetime. Bentley also photographed all forms of ice and natural water formations including clouds and fog. He was the first American to record raindrop sizes and was one of the first cloud physicists.
Image 21Surface irrigation system using siphon tubes
Rain is an oil-on-canvas painting by Dutch painter Vincent van Gogh, part of The Wheat Field, a series that he executed in 1889 while a voluntary patient in the Saint-Paul asylum near Saint-Rémy-de-Provence, France. Through his cell window on the upper floor, he could see an enclosed wheat field, and he made about a dozen paintings of it over the changing seasons. In this work, he represented falling rain with diagonal lines of paint. The style is reminiscent of Japanese prints, but the effect is stylistically personal to Van Gogh. Seen through his rain-splattered window, he shows its bleak aspect in November, with grey clouds overhead and the wheat already harvested. The painting is now in the collection of the Philadelphia Museum of Art.
Image 5Temperature distribution in a lake in summer and winter (from Properties of water)
Image 6The solid/liquid/vapor triple point of liquid water, ice Ih and water vapor in the lower left portion of a water phase diagram. (from Properties of water)
Image 9Heat of vaporization of water from melting to critical temperature (from Properties of water)
Image 10Temperature dependence of the surface tension of pure water (from Properties of water)
Image 11Estimates of changes in water storage around the Tigris and Euphrates Rivers, measured by NASA's GRACE satellites. The satellites measure tiny changes in gravitational acceleration, which can then be processed to reveal movement of water due to changes in its total mass. (from Hydrology)
Image 12Total renewable water resources per capita in 2020 (from Drinking water)
Image 13Example for physical and chemical parameters measured in drinking water samples in Kenya and Ethiopia as part of a systematic review of published literature. (from Drinking water)
Image 19Rain over a Scottish catchment. Understanding the cycling of water into, through, and out of catchments is a key element of hydrology. (from Hydrology)
Image 20World map for SDG 6 Indicator 6.1.1 in 2015: "Proportion of population using safely managed drinking water services" (from Drinking water)
Image 22This paper clip is under the water level, which has risen gently and smoothly. Surface tension prevents the clip from submerging and the water from overflowing the glass edges. (from Properties of water)
Image 26Poverty often leads to unhygienic living conditions, as in this community in the Indian Himalayas. Such conditions promote contraction of diarrheal diseases, as a result of contaminated drinking water, poor sanitation and hygiene. (from Drinking water)
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