Distribution of freshwater resources by type
68-799: WEAP (the Water Evaluation and Planning system ) is a model-building tool for water resource planning and policy analysis that is distributed at no charge to non-profit, academic, and governmental organizations in developing countries. WEAP can be used to create simulations of water demand , supply , runoff, evapotranspiration , water allocation, infiltration , crop irrigation requirements, instream flow requirements, ecosystem services , groundwater and surface storage, reservoir operations, pollution generation, treatment, discharge, and instream water quality . The simulations can be created under scenarios of varying policy, hydrology , climate, land use, technology, and socio-economic factors. WEAP links to
136-448: A basic drinking water service in 2017. Of those, 159 million people worldwide drink water directly from surface water sources, such as lakes and streams. One in eight people in the world do not have access to safe water. The world's supply of groundwater is steadily decreasing. Groundwater depletion (or overdrafting ) is occurring for example in Asia, South America and North America. It
204-426: A dynamic interface between surface water and groundwater from aquifers, exchanging flow between rivers and aquifers that may be fully charged or depleted. This is especially significant in karst areas where pot-holes and underground rivers are common. There are several artificial sources of fresh water. One is treated wastewater ( reclaimed water ). Another is atmospheric water generators . Desalinated seawater
272-630: A holistic way of managing water resources began already in the 1950s leading up to the 1977 United Nations Water Conference. The development of IWRM was particularly recommended in the final statement of the ministers at the International Conference on Water and the Environment in 1992, known as the Dublin Statement . This concept aims to promote changes in practices which are considered fundamental to improved water resource management . IWRM
340-590: A key role in water resource management agricultural irrigation . Evapotranspiration is defined as: "The combined processes through which water is transferred to the atmosphere from open water and ice surfaces, bare soil and vegetation that make up the Earth’s surface." Evapotranspiration is a combination of evaporation and transpiration, measured in order to better understand crop water requirements, irrigation scheduling, and watershed management. The two key components of evapotranspiration are: Evapotranspiration
408-419: A small discharge to each plant. Micro-irrigation uses less pressure and water flow than sprinkler irrigation. Drip irrigation delivers water directly to the root zone of plants. Subirrigation has been used in field crops in areas with high water tables for many years. It involves artificially raising the water table to moisten the soil below the root zone of plants. It is estimated that 22% of worldwide water
476-524: A surface and the ability of the surface to supply moisture, then PET is a measure of the demand side (also called evaporative demand ). Surface and air temperatures, insolation , and wind all affect this. A dryland is a place where annual potential evaporation exceeds annual precipitation . Often a value for the potential evapotranspiration is calculated at a nearby climatic station on a reference surface, conventionally on land dominated by short grass (though this may differ from station to station). This value
544-450: Is pollution . Pollution includes discharged solutes and increased water temperature ( thermal pollution ). It is estimated that 8% of worldwide water use is for domestic purposes. These include drinking water , bathing , cooking , toilet flushing , cleaning, laundry and gardening . Basic domestic water requirements have been estimated by Peter Gleick at around 50 liters per person per day, excluding water for gardens. Drinking water
612-437: Is water scarcity , water pollution , water conflict and climate change . Fresh water is in principle a renewable resource . However, the world's supply of groundwater is steadily decreasing. Groundwater depletion (or overdrafting ) is occurring for example in Asia, South America and North America. Natural sources of fresh water include surface water , under river flow, groundwater and frozen water . Surface water
680-403: Is a comprehensive, participatory planning and implementation tool for managing and developing water resources in a way that balances social and economic needs, and that ensures the protection of ecosystems for future generations. In addition, in light of contributing the achievement of Sustainable Development goals (SDGs) , IWRM has been evolving into more sustainable approach as it considers
748-420: Is a long-established practice. This is especially so in arid countries. Reusing wastewater as part of sustainable water management allows water to remain an alternative water source for human activities. This can reduce scarcity . It also eases pressures on groundwater and other natural water bodies. Desalination is a process that removes mineral components from saline water . More generally, desalination
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#1732844546213816-414: Is a reflection of the energy available to evaporate or transpire water, and of the wind available to transport the water vapor from the ground up into the lower atmosphere and away from the initial location. Potential evapotranspiration is expressed in terms of a depth of water or soil moisture percentage. If the actual evapotranspiration is considered the net result of atmospheric demand for moisture from
884-441: Is also employed to protect crops from frost , suppress weed growth in grain fields, and prevent soil consolidation . It is also used to cool livestock , reduce dust , dispose of sewage , and support mining operations. Drainage , which involves the removal of surface and sub-surface water from a given location, is often studied in conjunction with irrigation. There are several methods of irrigation that differ in how water
952-413: Is also known as groundwater recharge . Reused water also serve various needs in residences such as toilet flushing , businesses, and industry. It is possible to treat wastewater to reach drinking water standards. Injecting reclaimed water into the water supply distribution system is known as direct potable reuse. Drinking reclaimed water is not typical. Reusing treated municipal wastewater for irrigation
1020-520: Is an important consideration. Some human water users have an intermittent need for water. For example, many farms require large quantities of water in the spring, and no water at all in the winter. Other users have a continuous need for water, such as a power plant that requires water for cooling. Over the long term the average rate of precipitation within a watershed is the upper bound for average consumption of natural surface water from that watershed. Irrigation (also referred to as watering of plants)
1088-728: Is another important source. It is important to consider the economic and environmental side effects of these technologies. Water reclamation is the process of converting municipal wastewater or sewage and industrial wastewater into water that can be reused for a variety of purposes . It is also called wastewater reuse, water reuse or water recycling. There are many types of reuse. It is possible to reuse water in this way in cities or for irrigation in agriculture. Other types of reuse are environmental reuse, industrial reuse, and reuse for drinking water, whether planned or not. Reuse may include irrigation of gardens and agricultural fields or replenishing surface water and groundwater . This latter
1156-419: Is areas with high water tables , where capillary action can cause water from the groundwater to rise through the soil matrix back to the surface. If potential evapotranspiration is greater than the actual precipitation, then soil will dry out until conditions stabilize, unless irrigation is used. Evapotranspiration can be measured directly with a weighing or pan lysimeter . A lysimeter continuously measures
1224-446: Is by calculating the energy balance. λ E = R n − G − H {\displaystyle \lambda E=R_{n}-G-H\,\!} where λE is the energy needed to change the phase of water from liquid to gas, R n is the net radiation, G is the soil heat flux and H is the sensible heat flux . Using instruments like a scintillometer , soil heat flux plates or radiation meters,
1292-446: Is called the water table . Groundwater is recharged from the surface; it may discharge from the surface naturally at springs and seeps , and can form oases or wetlands . Groundwater is also often withdrawn for agricultural , municipal , and industrial use by constructing and operating extraction wells . The study of the distribution and movement of groundwater is hydrogeology , also called groundwater hydrology . Throughout
1360-418: Is called the reference evapotranspiration (ET 0 ). Actual evapotranspiration is said to equal potential evapotranspiration when there is ample water present. Evapotranspiration can never be greater than potential evapotranspiration, but can be lower if there is not enough water to be evaporated or plants are unable to transpire maturely and readily. Some US states utilize a full cover alfalfa reference crop that
1428-469: Is ever-increasing demand for drinking , manufacturing , leisure and agriculture . Due to the small percentage of water available, optimizing the fresh water we have left from natural resources has been a growing challenge around the world. Much effort in water resource management is directed at optimizing the use of water and in minimizing the environmental impact of water use on the natural environment. The observation of water as an integral part of
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#17328445462131496-537: Is handled differently by different countries. For example, in the United States , the United States Geological Survey (USGS) and its partners monitor water resources, conduct research and inform the public about groundwater quality. Water resources in specific countries are described below: Evapotranspiration Evapotranspiration ( ET ) refers to the combined processes which move water from
1564-460: Is lost or intentionally destroyed by clearing and burning, soil moisture is reduced by wind, and soils are easily eroded by high wind and rainfall events. In areas that are not irrigated, actual evapotranspiration is usually no greater than precipitation , with some buffer and variations in time depending on the soil's ability to hold water. It will usually be less because some water will be lost due to percolation or surface runoff . An exception
1632-609: Is low, and use the stored water to produce electricity when demand is high. Thermoelectric power plants using cooling towers have high consumption, nearly equal to their withdrawal, as most of the withdrawn water is evaporated as part of the cooling process. The withdrawal, however, is lower than in once-through cooling systems. Water is also used in many large scale industrial processes, such as thermoelectric power production, oil refining, fertilizer production and other chemical plant use, and natural gas extraction from shale rock . Discharge of untreated water from industrial uses
1700-576: Is one of the few water resources independent of rainfall. Researchers proposed air capture over oceans which would "significantly increasing freshwater through the capture of humid air over oceans" to address present and, especially, future water scarcity/insecurity. A 2021 study proposed hypothetical portable solar-powered atmospheric water harvesting devices . However, such off-the-grid generation may sometimes "undermine efforts to develop permanent piped infrastructure " among other problems. The total quantity of water available at any given time
1768-423: Is still unclear how much natural renewal balances this usage, and whether ecosystems are threatened. Water resource management is the activity of planning, developing, distributing and managing the optimum use of water resources. It is an aspect of water cycle management . The field of water resources management will have to continue to adapt to the current and future issues facing the allocation of water. With
1836-419: Is supplied to plants. Surface irrigation , also known as gravity irrigation, is the oldest form of irrigation and has been in use for thousands of years. In sprinkler irrigation , water is piped to one or more central locations within the field and distributed by overhead high-pressure water devices. Micro-irrigation is a system that distributes water under low pressure through a piped network and applies it as
1904-622: Is the Penman equation . The Penman–Monteith variation is recommended by the Food and Agriculture Organization and the American Society of Civil Engineers . The simpler Blaney–Criddle equation was popular in the Western United States for many years but it is not as accurate in wet regions with higher humidity. Other equations for estimating evapotranspiration from meteorological data include
1972-432: Is the practice of applying controlled amounts of water to land to help grow crops , landscape plants , and lawns . Irrigation has been a key aspect of agriculture for over 5,000 years and has been developed by many cultures around the world. Irrigation helps to grow crops, maintain landscapes, and revegetate disturbed soils in dry areas and during times of below-average rainfall. In addition to these uses, irrigation
2040-499: Is the removal of salts and minerals from a substance. One example is soil desalination . This is important for agriculture. It is possible to desalinate saltwater, especially sea water , to produce water for human consumption or irrigation. The by-product of the desalination process is brine . Many seagoing ships and submarines use desalination. Modern interest in desalination mostly focuses on cost-effective provision of fresh water for human use. Along with recycled wastewater , it
2108-443: Is to establish an inner, urban, water cycle loop through the implementation of reuse strategies. Developing this urban water cycle loop requires an understanding both of the natural, pre-development, water balance and the post-development water balance. Accounting for flows in the pre- and post-development systems is an important step toward limiting urban impacts on the natural water cycle. Water resource management and governance
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2176-459: Is typically measured in millimeters of water (i.e. volume of water moved per unit area of the Earth's surface) in a set unit of time. Globally, it is estimated that on average between three-fifths and three-quarters of land precipitation is returned to the atmosphere via evapotranspiration. Evapotranspiration does not, in general, account for other mechanisms which are involved in returning water to
2244-481: Is used in industry . Major industrial users include hydroelectric dams, thermoelectric power plants , which use water for cooling , ore and oil refineries , which use water in chemical processes , and manufacturing plants, which use water as a solvent . Water withdrawal can be very high for certain industries, but consumption is generally much lower than that of agriculture. Water is used in renewable power generation. Hydroelectric power derives energy from
2312-510: Is water in a river, lake or fresh water wetland . Surface water is naturally replenished by precipitation and naturally lost through discharge to the oceans , evaporation , evapotranspiration and groundwater recharge . The only natural input to any surface water system is precipitation within its watershed . The total quantity of water in that system at any given time is also dependent on many other factors. These factors include storage capacity in lakes, wetlands and artificial reservoirs ,
2380-417: Is water that is of sufficiently high quality so that it can be consumed or used without risk of immediate or long term harm. Such water is commonly called potable water. In most developed countries, the water supplied to domestic, commerce and industry is all of drinking water standard even though only a very small proportion is actually consumed or used in food preparation. 844 million people still lacked even
2448-523: The Makkink equation , which is simple but must be calibrated to a specific location, and the Hargreaves equations . To convert the reference evapotranspiration to the actual crop evapotranspiration, a crop coefficient and a stress coefficient must be used. Crop coefficients, as used in many hydrological models, usually change over the year because crops are seasonal and, in general, plant behaviour varies over
2516-738: The USGS MODFLOW groundwater flow model and the US EPA QUAL2K surface water quality model. WEAP was created in 1988 and continues to be developed and supported by the U.S. Center of the Stockholm Environment Institute , a non-profit research institute based at Tufts University in Somerville , Massachusetts. It is used for climate change vulnerability studies and adaptation planning and has been applied by researchers and planners in thousands of organizations worldwide. Establishing
2584-597: The ecosystem is based on integrated water resources management , based on the 1992 Dublin Principles (see below). Sustainable water management requires a holistic approach based on the principles of Integrated Water Resource Management , originally articulated in 1992 at the Dublin (January) and Rio (July) conferences. The four Dublin Principles, promulgated in the Dublin Statement are: Implementation of these principles has guided reform of national water management law around
2652-715: The global surface temperature ); and thirdly the ability of the atmosphere to take up water ( humidity ). Regarding the second factor (energy and heat): climate change has increased global temperatures (see instrumental temperature record ). This global warming has increased evapotranspiration over land. The increased evapotranspiration is one of the effects of climate change on the water cycle . Vegetation type impacts levels of evapotranspiration. For example, herbaceous plants generally transpire less than woody plants , because they usually have less extensive foliage. Also, plants with deep reaching roots can transpire water more constantly, because those roots can pull more water into
2720-402: The sustainability of the current and future water resource allocation. Sustainable Development Goal 6 has a target related to water resources management: "Target 6.5: By 2030, implement integrated water resources management at all levels, including through transboundary cooperation as appropriate." At present, only about 0.08 percent of all the world's fresh water is accessible. And there
2788-434: The water balance equation for a given area:. The water balance equation relates the change in water stored within the basin ( S ) to its input and outputs: Δ S = P − E T − Q − D {\displaystyle \Delta S=P-ET-Q-D\,\!} In the equation, the change in water stored within the basin ( ΔS ) is related to precipitation ( P ) (water going into
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2856-426: The Earth's surface (open water and ice surfaces, bare soil and vegetation ) into the atmosphere . It covers both water evaporation (movement of water to the air directly from soil, canopies , and water bodies) and transpiration (evaporation that occurs through the stomata , or openings, in plant leaves). Evapotranspiration is an important part of the local water cycle and climate , and measurement of it plays
2924-487: The Nexus approach, which is a cross-sectoral water resource management. The Nexus approach is based on the recognition that "water, energy and food are closely linked through global and local water, carbon and energy cycles or chains." An IWRM approach aims at avoiding a fragmented approach of water resources management by considering the following aspects: Enabling environment, roles of Institutions, management Instruments. Some of
2992-417: The atmosphere, though some of these, such as snow and ice sublimation in regions of high elevation or high latitude, can make a large contribution to atmospheric moisture even under standard conditions. Levels of evapotranspiration in a given area are primarily controlled by three factors: Firstly, the amount of water present. Secondly, the amount of energy present in the air and soil (e.g. heat, measured by
3060-406: The basin), and evapotranspiration ( ET ), streamflow ( Q ), and groundwater recharge ( D ) (water leaving the basin). By rearranging the equation, ET can be estimated if values for the other variables are known: E T = P − Δ S − Q − D {\displaystyle ET=P-\Delta S-Q-D\,\!} A second methodology for estimation
3128-401: The competing demands for water and seeks to allocate water on an equitable basis to satisfy all uses and demands. As with other resource management , this is rarely possible in practice so decision-makers must prioritise issues of sustainability, equity and factor optimisation (in that order!) to achieve acceptable outcomes. One of the biggest concerns for water-based resources in the future is
3196-692: The components of the energy balance can be calculated and the energy available for actual evapotranspiration can be solved. The SEBAL and METRIC algorithms solve for the energy balance at the Earth's surface using satellite imagery. This allows for both actual and potential evapotranspiration to be calculated on a pixel-by-pixel basis. Evapotranspiration is a key indicator for water management and irrigation performance. SEBAL and METRIC can map these key indicators in time and space, for days, weeks or years. Given meteorological data like wind, temperature, and humidity, reference ET can be calculated. The most general and widely used equation for calculating reference ET
3264-411: The course of a river, the total volume of water transported downstream will often be a combination of the visible free water flow together with a substantial contribution flowing through rocks and sediments that underlie the river and its floodplain called the hyporheic zone . For many rivers in large valleys, this unseen component of flow may greatly exceed the visible flow. The hyporheic zone often forms
3332-440: The cross-cutting conditions that are also important to consider when implementing IWRM are: Political will and commitment, capacity development, adequate investment, financial stability and sustainable cost recovery, monitoring and evaluation. There is not one correct administrative model. The art of IWRM lies in selecting, adjusting and applying the right mix of these tools for a given situation. IWRM practices depend on context; at
3400-583: The force of water flowing downhill, driving a turbine connected to a generator. This hydroelectricity is a low-cost, non-polluting, renewable energy source. Significantly, hydroelectric power can also be used for load following unlike most renewable energy sources which are intermittent . Ultimately, the energy in a hydroelectric power plant is supplied by the sun. Heat from the sun evaporates water, which condenses as rain in higher altitudes and flows downhill. Pumped-storage hydroelectric plants also exist, which use grid electricity to pump water uphill when demand
3468-423: The greatest area of glaciers and permafrost outside of the poles. Ten of Asia's largest rivers flow from there, and more than a billion people's livelihoods depend on them. To complicate matters, temperatures there are rising more rapidly than the global average. In Nepal, the temperature has risen by 0.6 degrees Celsius over the last decade, whereas globally, the Earth has warmed approximately 0.7 degrees Celsius over
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#17328445462133536-489: The growing uncertainties of global climate change and the long-term impacts of past management actions, this decision-making will be even more difficult. It is likely that ongoing climate change will lead to situations that have not been encountered. As a result, alternative management strategies, including participatory approaches and adaptive capacity are increasingly being used to strengthen water decision-making. Ideally, water resource management planning has regard to all
3604-442: The implementation of IWRM at a global level. The third World Water Forum recommended IWRM and discussed information sharing, stakeholder participation, and gender and class dynamics. Operationally, IWRM approaches involve applying knowledge from various disciplines as well as the insights from diverse stakeholders to devise and implement efficient, equitable and sustainable solutions to water and development problems. As such, IWRM
3672-474: The last hundred years. Groundwater is the water present beneath Earth 's surface in rock and soil pore spaces and in the fractures of rock formations . About 30 percent of all readily available fresh water in the world is groundwater. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water
3740-502: The liquid water in fog or low clouds onto their surface, which eventually drips down to the ground. These trees still contribute to evapotranspiration, but often collect more water than they evaporate or transpire. In rainforests, water yield is increased (compared to cleared, unforested land in the same climatic zone) as evapotranspiration increases humidity within the forest (a portion of which condenses and returns quickly as precipitation experienced at ground level as rain). The density of
3808-411: The operational level, the challenge is to translate the agreed principles into concrete action. Integrated urban water management (IUWM) is the practice of managing freshwater , wastewater , and storm water as components of a basin-wide management plan. It builds on existing water supply and sanitation considerations within an urban settlement by incorporating urban water management within
3876-438: The permeability of the soil beneath these storage bodies, the runoff characteristics of the land in the watershed, the timing of the precipitation and local evaporation rates. All of these factors also affect the proportions of water loss. Humans often increase storage capacity by constructing reservoirs and decrease it by draining wetlands. Humans often increase runoff quantities and velocities by paving areas and channelizing
3944-558: The plant and leaves. Another example is that conifer forests tend to have higher rates of evapotranspiration than deciduous broadleaf forests, particularly in the dormant winter and early spring seasons, because they are evergreen . Transpiration is a larger component of evapotranspiration (relative to evaporation) in vegetation-abundant areas. As a result, denser vegetation, like forests, may increase evapotranspiration and reduce water yield. Two exceptions to this are cloud forests and rainforests . In cloud forests, trees collect
4012-506: The resultant economic and social welfare in an equitable manner without compromising the sustainability of vital ecosystems ". Some scholars say that IWRM is complementary to water security because water security is a goal or destination, whilst IWRM is the process necessary to achieve that goal. IWRM is a paradigm that emerged at international conferences in the late 1900s and early 2000s, although participatory water management institutions have existed for centuries. Discussions on
4080-442: The scope of the entire river basin. IUWM is commonly seen as a strategy for achieving the goals of Water Sensitive Urban Design . IUWM seeks to change the impact of urban development on the natural water cycle , based on the premise that by managing the urban water cycle as a whole; a more efficient use of resources can be achieved providing not only economic benefits but also improved social and environmental outcomes. One approach
4148-506: The stream flow. Natural surface water can be augmented by importing surface water from another watershed through a canal or pipeline . Brazil is estimated to have the largest supply of fresh water in the world, followed by Russia and Canada . Glacier runoff is considered to be surface water. The Himalayas, which are often called "The Roof of the World", contain some of the most extensive and rough high altitude areas on Earth as well as
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#17328445462134216-465: The vegetation blocks sunlight and reduces temperatures at ground level (thereby reducing losses due to surface evaporation), and reduces wind speeds (thereby reducing the loss of airborne moisture). The combined effect results in increased surface stream flows and a higher ground water table whilst the rainforest is preserved. Clearing of rainforests frequently leads to desertification as ground level temperatures and wind speeds increase, vegetation cover
4284-548: The water on Earth is salt water and only three percent is fresh water ; slightly over two-thirds of this is frozen in glaciers and polar ice caps . The remaining unfrozen freshwater is found mainly as groundwater, with only a small fraction present above ground or in the air. Natural sources of fresh water include surface water , under river flow, groundwater and frozen water . People use water resources for agricultural , industrial and household activities. Water resources are under threat from multiple issues. There
4352-541: The weight of a plant and associated soil, and any water added by precipitation or irrigation. The change in storage of water in the soil is then modeled by measuring the change in weight. When used properly, this allows for precise measurement of evapotranspiration over small areas. Because atmospheric vapor flux is difficult or time-consuming to measure directly, evapotranspiration is typically estimated by one of several different methods that do not rely on direct measurement. Evapotranspiration may be estimated by evaluating
4420-568: The world since 1992. Further challenges to sustainable and equitable water resources management include the fact that many water bodies are shared across boundaries which may be international (see water conflict ) or intra-national (see Murray-Darling basin ). Integrated water resources management (IWRM) has been defined by the Global Water Partnership (GWP) as "a process which promotes the coordinated development and management of water, land and related resources, in order to maximize
4488-419: The year: perennial plants mature over multiple seasons, while annuals do not survive more than a few , so stress responses can significantly depend upon many aspects of plant type and condition. Potential evapotranspiration (PET) or potential evaporation (PE) is the amount of water that would be evaporated and transpired by a specific crop , soil or ecosystem if there was sufficient water available. It
4556-645: The ‘current accounts’ and building scenarios and evaluating the scenarios about criteria are the main WEAP applications in Simulation problems. Water resource Water resources are natural resources of water that are potentially useful for humans, for example as a source of drinking water supply or irrigation water. These resources can be either freshwater from natural sources, or water produced artificially from other sources, such as from reclaimed water ( wastewater ) or desalinated water ( seawater ). 97% of
4624-687: Was a topic of the second World Water Forum , which was attended by a more varied group of stakeholders than the preceding conferences and contributed to the creation of the GWP. In the International Water Association definition, IWRM rests upon three principles that together act as the overall framework: In 2002, the development of IWRM was discussed at the World Summit on Sustainable Development held in Johannesburg, which aimed to encourage
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