There is a new generation of super-rich, highly influential people who are starting to invest massive amounts of money and influence in truly important causes. Bill and Melinda Gates in global health, Warren Buffett in reproductive health and food, the Jolie-Pitts in community development, and the Katrina recovery effort. Now, enter Matt Damon and Gary White who have co-founded water.org, an organization dedicated to developing and delivering solutions to the global water crisis. Visit water.org [2] and you will find an impressive array of information and programs. Here are direct facts from that site that convey the magnitude of the current global water emergency.
More than any other resource, with the exception of food, water is crucial for human survival. Ancient civilizations were repeatedly forced to deal with the threat of diminishing water supply. Now, climate change presents a new threat by causing the supply and distribution of water to change over the coming decades and centuries. This situation will be made significantly more dire by explosive population growth in parts of the world where water is scarce and by pollution that will continually limit the supply of clean drinking water. The IPCC (2007) stated the situation very clearly: “Water and its availability and quality, will be the main pressures on, and issues for, societies and the environment under climate change.” The latest 2022 report stresses the need for adaptation. This will be much easier in the developed world than in developing countries where resources are limited.
Because groundwater systems recover very slowly from human impacts, remediation can be extremely difficult and expensive. In this module, we begin by examining the distribution and behavior of water close to the Earth’s surface; next, we consider how climate change will alter the supply of water and how population growth will change the demand; finally, we present management strategies that will hopefully preserve the supply of water for humans around the globe.
Ancient civilizations developed in some of the driest realms of the planet. Populations in Egypt and Mesopotamia (an area that includes parts of modern Iran, Iraq, Syria, and Turkey) learned how to survive in an arid environment. For example, ancient Egyptians and Mesopotamians constructed an extensive network of canals to transport water away from the Nile River for irrigation. Shadufs, which are contraptions consisting of buckets at the end of a boom which could be lowered with a rope, were used to haul water out of the canals and onto the fields. These civilizations routinely had to live with highly irregular precipitation consisting of periods when large amounts of rainfall flowed through the canals and flooded large areas, alternating with times of almost no rainfall.
As the population has increased, and especially with the rise of industry in developed nations, so has demand for water soared. Moreover, industry has increased competition often for the cleanest drinking water supplies.
Nowhere has the interplay between the increasing demand and limited supply of water been more complicated than in the desert southwest of the US. The city of Los Angeles receives a meager 38 cm (15 in) of rain a year. Yet, the city has the highest water usage in California and some of the highest use rates in the country. You would never know by looking at the number of golf courses and car washes and the abundance of lush, green lawns that the city is located in a desert. The same is true for Las Vegas, which receives significantly lower rainfall and is one of the fastest growing cities in the US.
Los Angeles uses much more water than it receives from precipitation and, thus, it imports water from the northern part of California and from states to the east via the Colorado River. In fact, much of the development of Los Angeles was fueled by this supply of water from the Owens Valley in the Sierra Nevada and the Colorado River to the east. Water from the Colorado River began to flow into Los Angeles in the 1920s and 1930s and included the construction of Parker Dam and the Colorado River Aqueduct.
The growth of other cities that lie in arid locations closer to the Colorado River, including Denver and Phoenix, will likely lead to bitter litigation over water rights in the southwest in the coming decades. Water supply to the Colorado River is declining markedly as a result of climate change and this is clashing with booming growth of these soutwestern cities. In Spring 2023, the US government brokered a deal with the southwestern states that includes a 13 percent decrease in water supply from the river. This will mandate major consrvation efforts and slower growth. Overseas, countries in arid parts of the globe, for example, Turkey, Iraq, and Syria have also had major disputes about water rights and management. Turkey, which lies at the source of the Tigris and Euphrates rivers, has constructed dams on both rivers for irrigation purposes as well as for hydroelectricity, and this has led to long conflicts with countries downriver including Syria and Iraq.
With projections for the increasingly rapid growth of world population and coupled demand for water for drinking and agriculture, as well as for industry, maintaining a clean water supply looks to be one of the grand challenges of the 21st century. The goals of this module are to learn about how water is cycled on the Earth’s surface and how climate change coupled with the growth of the population will accentuate the global water crisis.
On completing this module, students are expected to be able to:
After completing this module, students should be able to explain the following concepts:
Below is an overview of your assignments for this module. The list is intended to prepare you for the module and help you to plan your time.
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The distribution of water on the Earth’s surface is extremely uneven. Only 3% of water on the surface is fresh; the remaining 97% resides in the ocean. Of freshwater, 69% resides in glaciers, 30% underground, and less than 1% is located in lakes, rivers, and swamps. Looked at another way, only one percent of the water on the Earth’s surface is usable by humans, and 99% of the usable quantity is situated underground.
All one needs to do is study rainfall maps to appreciate how uneven the distribution of water really is. The white areas on the map below had annual rainfall under 400 mm for the last year, which makes them semi-arid or arid. And, remember, projections are for significant aridification to occur in many dry regions and for more severe rainfall events to characterize wet regions.
The following video provides a schematic summary of the water cycle.
The hydrologic cycle describes the large-scale movement of water between reservoirs including the ocean, rivers and lakes, the atmosphere, ice sheets, and underground storage or groundwater.
Water evaporates from bodies of water such as the ocean and lakes to form clouds. The moisture in clouds ultimately falls as rain or snow, some of which returns back to the ocean, lakes, and rivers. The remainder percolates into the soil, where it reacts with organic material and minerals and ultimately moves downwards to form groundwater. The amount that percolates depends strongly on evaporation as well as soil moisture, as shown in the video below.
Video: NASA Land Globe Animation (1:00) This video is not narrated.
Freshwater used for drinking, agriculture, and industry derives dominantly from rivers, lakes, and groundwater, with the latter reservoir accounting for approximately 30 percent of freshwater on the earth’s surface by % of potable (i.e., safe drinking) water. In the US, 86% of households derive water from public suppliers, and 14% supply their own water from wells. Nevertheless, households utilize only one percent of water extracted, the remaining 99% of water is supplied to industry (4%), agriculture (37% compared to 69% worldwide), and thermoelectric power plants (41%). Water use in most areas of the US has increased substantially over the last century.
Download this lab as a Word document: Lab 8: Stream Flow [7] (Please download required files below.)
In this lab, we will observe the impact of precipitation on stream flow and flooding. The practice and graded sequence of steps are identical. Please go through the following sequence of questions for the practice, check your answers in the Practice Lab, then take the Graded Lab when ready.
The US Geological Survey maintains the water watch website, which shows the current state of stream flow, drought, flood, and past flow and runoff. We will focus on stream flow data, and you will be required to summarize national trends. The data are expressed as percentiles over normal stream flow for the date of interest. The site has an animation builder [8] that allows you to observe changes in stream flow over short periods and intervals back to 1999. The animations show both regular stream flow and flood stage locations.
Observe the flood and stream flow animations for the following intervals, and describe what you see in terms of major floods and general stream flow. (You can toggle back and forth between these two kinds of animations using the Map Type menu on the animation panel; Real-Time is general stream flow, while the Flood maps show black triangles for places where the streams are actually flooding above their banks.)
Using the USGS animation builder [8], answer the following practice questions:
Because of the significance of this groundwater for human use, we consider the behavior of water underground in some detail here. It might seem complex at first, but water flow follows very simple laws of physics.
Water at the surface of the Earth seeps slowly into the soil, a process known as percolation. Water will percolate through the uppermost layer of soil and loose material that contains air, the aerated zone, down to a level called the water table. The water table is at the top of the permanently waterlogged or saturated level.
The water table is a critical level because it determines the level of groundwater available for drinking and irrigation. The flow of water underground is controlled by a number of factors, including the permeability of the aquifer and the hydraulic gradient. Explained simply, the hydraulic gradient between two wells is the difference in hydraulic pressure (known as hydraulic head) divided by the distance between them. If the difference in hydraulic head is high, water will flow readily; if the difference is nil, then water will only flow if pumped. The hydraulic gradient at points at the top of the water table is generally level.
The permeability of a rock is a function of a number of factors that include the amount of pore space, the arrangement of pores, and the amount of surface tension from grains, especially tiny (micron-sized) clay minerals that have very high surface area. The larger the pore space, the more connected the grains and the less clay, the higher the permeability, and the more easily water flows. Conversely, where pore space is tight and poorly connected, and there is a lot of clay, permeability is low and water cannot flow readily.
The best aquifers are often made of rocks with both high porosity and high permeability, such as sandstone, but rocks with generally lower porosity can also be highly permeable. For example, limestone is often jointed and is readily dissolved by groundwater, leaving the rock highly permeable; rocks such as granite and basalt are often heavily fractured allowing water to flow readily. Some of the most productive aquifers are called “contained” or “confined,” and are sandwiched between low-permeability layers called “aquicludes.” Common aquicludes are shale and mudstone layers. Such contained aquifers can have a high hydraulic gradient because the aquicludes hold a significant hydraulic head; confined aquifers often produce wells called artesian wells that, owing to substantial confining pressure, produce water without pumping.
In other cases, the tops of aquifers are not confined by an impermeable layer. Such aquifers are called unconfined and will, all other things being equal, be characterized by less confining pressure. Groundwater is continuously exchanging with other reservoirs in the hydrological cycle. Aquifers are recharged with water from rain and snow percolating through the aerated zone. Conversely, groundwater flows back into rivers and lakes or into wells and springs in a process known as discharge. The time water spends underground is called the residence time, which varies from a few days to 10,000 years or more. As we will see later, the water table can move downward as a result of drought, and this is happening in arid areas today.
Communities around the world are facing a variety of different problems related to the supply of water. Many of these are not new, having been faced by ancient civilizations, for example, the problem of irrigation in desert regions. A number of problems are becoming more urgent as a result of population growth and demand on aquifers. Improving understanding of groundwater behavior and remediation and advancing technology are helping to solve some of the most pressing problems; however, many groundwater issues continue to become more dire through time, especially in developing nations. Here, we discuss some of the most pressing problems. We stress that these problems are experienced globally, although we provide regional and local examples.
Like any layer in the subsurface, aquifers, and aquitards structurally support the overlying strata, and in turn, the ground level. If an aquifer is excessively pumped, water is drawn in from the surrounding aquitards. In cases where the aquitards are soft and unconsolidated, for example, composed of clays and silts, overpumping can cause these layers to fail structurally, expel much of their water, and literally collapse. When this happens, the overlying ground level can be lowered as a consequence, a process known as subsidence.
In the case of arid regions where aquifers are naturally recharged at very slow rates and where they are pumped intensively, significant subsidence can result. Some of the most drastic and best-known subsidence resulting from overuse of aquifers occurs in the San Joaquin and Sacramento Valleys of California, where the land level has subsided up to 10 meters in the last 90 years.
The San Joaquin and Sacramento rivers flow together in an area called the Sacramento-San Joaquin River Delta, an inland version of the Mississippi Delta where a series of tributary channels meander over a low-lying, flat plain. The area is an inland estuary with the Pacific Ocean on its western edge. The Delta area, as it is known, is some of the most productive farmland in the nation and provides 70% of the water supply of northern California. The water in the Delta channels has been controlled by human-made earthen levees to prevent flooding of low-lying agricultural areas as well as large developed areas including parts of the cities of Tracy, Stockton, and Sacramento. The 2600 mile long levee system has been built over more than 100 years and is beginning to suffer from the test of time. Subsidence has occurred as a result of oxidation of organic material in soils and compaction from farming, and the structures have been weakened by erosion and seepage. Areas behind the levees have subsided by up to 25 feet, placing further strain on the structures. Failure of levees has already occurred over 30 times in the last three decades, leading to substantial flooding, massive evacuation and six fatalities in Marysville in 1997.
Levees in the delta are maintained by the Army Corps of Engineers to withhold the strain of a 100-year flood. However, increased precipitation as a result of climate change has led some to question the Corps’ definition of the 100-year flood, and the same critics warn of catastrophic levee collapse, which could lead to massive numbers of fatalities and enormous property damage. Ultimately, what is required is a significant investment in fortifying levees to prevent this from happening.
Subsidence as a result of overpumping is actually a relatively common problem, especially in areas with rapid population growth, for example around Las Vegas, which until recently was the most rapidly growing city in the US. In Las Vegas, water use has exceeded recharge for many decades, leading to structurally controlled subsidence of up to 2 meters along pre-existing geological faults. Subsidence of some 3 meters has also occurred in the area around Houston as a result of population growth combined with extraction of large amounts of oil and gas from the subsurface.
As we will study in detail in Module 10, significant subsidence in the Mississippi Delta region around New Orleans has resulted partially as a result of over-pumping. Even along the east coast of the US in the Carolinas, subsidence, although not as severe as out west and along the Gulf Coast, has resulted from over pumping for agriculture and industry. In fact, one of the major demands on water in the Carolinas is for golf courses (see the lush grass in the photograph above), which account for about 60% of irrigation usage in some areas.
Without major changes in water usage and conservation, subsidence will continue and even accelerate into the foreseeable future.
Overuse of groundwater does not have to lead to major land subsidence before it causes problems. On a more local scale, over-pumping can result in lowering of the water table in a process called “cone of depression,” a generally concentric pattern of water table drawdown. Such over-pumping often results from industry or agriculture, but individual landowners often feel the repercussions.
Alternatively, a cone of depression can result when housing developments, particularly those with many small lots, use wells for water supply. A cone of depression can drastically decrease water pressure, or worse, lower the water table below the level of the well, leaving a home or a farm without a water supply. The only solution for this is to drill the well deeper, which can be an expensive proposition for an individual landowner. Left unchecked, a cone of depression can modify the flow of groundwater as well as the distribution of pollutants,
Contamination of groundwater supply can occur as a result of natural processes as well as industry and agriculture. Probably, the most lethal and extensive groundwater pollution problem globally is actually natural in origin: the contamination of groundwater with high concentrations of arsenic. Approximately 100 million people globally are exposed to high levels of arsenic in groundwater. Nowhere is the problem more devastating than over large regions of Bangladesh and the West Bengal region of India, where millions have been poisoned by arsenic. This area is intensively irrigated, which has changed the flow of groundwater over a large region. As a result, a shallow aquifer is the source of groundwater for 35-77 million inhabitants who obtain their water from shallow tube wells.
High levels of arsenic in this water likely derive from microbial activity that dissociates arsenic from organic material. Arsenic is highly poisonous and carcinogenic and long-term exposure to it can lead to high incidences of skin lesions, bladder, lung, skin and kidney cancer, respiratory disease, and liver and kidney disease. Because the threatened regions are heavily populated, this pollution has made millions of people sick and caused thousands of deaths each year. Even though the hydrology of the affected areas is not well understood, the solution to the arsenic contamination issue involves a combination of extensive monitoring, closing down high-concentration wells, distribution of filters and chemicals to remove arsenic from drinking water, and ultimately tapping deeper aquifers.
Pollution from agricultural and industrial sources is common, although not always as lethal as arsenic poisoning. Typical sources of industrial pollution include solvents, gasoline and other hydrocarbons, paint, and heavy metals. Pollution from agricultural sources includes pesticides, herbicides, and fertilizers. Many of these pollutants are carcinogenic. Both sources of pollution can lead to the growth of toxic microbes. Agricultural and industrial runoff can deliver pollutants into groundwater systems
Human and agricultural sewage is another potential source of pollution. This pollution leads to a variety of different impacts on health all the way from gastrointestinal illness to, in severe cases, cholera, typhoid, amoebiasis, giardiasis, and E. coli.
You can’t mention lead in groundwater without telling the terrible story of Flint, Michigan. Flint has had a rough economic time with General Motors pulling out of the city in the 1980s, and this is partially responsible for significant unemployment and high levels of poverty. The city is 57% African American. Minority communities have been subject to terrible inequity in terms of access to clean air and drinking water, and Flint is one of the most devastating cases of all.
The city used to derive its water supply from Lake Huron, as did the city of Detroit. This high-quality water was very expensive, and as the city was carrying great debt, back in Spring 2014 the state decided to switch the water management agency and at the same time to supply water to the city from the Flint River. Treating water from a river is far more difficult than treating water from a lake, and the processing facility wasn’t equipped to handle the poor quality of the river water. In particular, the water wasn’t treated with additives to lower its corrosiveness. Moreover, the water had very high levels of bacteria. So the end result was the water delivered to the citizens of Flint came out of the faucets dirty, smelling bad and tasting terrible. Even after citizens protested and showed jugs of this nasty water, officials told them the water was safe to drink. Turns out the water was so corrosive that it stripped lead from the antiquated pipe system of the city. In most cities, old pipes have been replaced, but that was not the case in Flint.
The high levels of the bacterial Legionella led to an outbreak of Legionnaires Disease. This waterborne disease causes a severe flu including respiratory, gastrointestinal and even neurological symptoms, and it can be fatal. In Flint, 12 people died and almost 90 became sick. There have been numerous investigations of the connections between Legionnaires and the Flint drinking water, and in all the most logical finding is that the high bacterial levels were a result of low chlorine in the water because it had reacted with the high lead and iron levels.
But the lead is what is likely to cause the most permanent damage, 100,000 people were exposed to high lead levels including about 9,000 children who drank this dangerous water for up to 18 months. And it took the state 9 months to inform the citizens that they had discovered the lead. Children are more susceptible to long term impact of lead poisoning because their bodies are developing. Lead exposure can cause permanent brain damage, learning and development problems including lower IQ and speech and hearing issues lasting for a lifetime. Tests showed that lead levels had doubled or tripled in Flint children.
The city switched back to old water supply in October 2015, but that was not the end of the story. Lead was still in the water because of the damage to the pipes. The outrage from Flint citizens was a major reason for the state and federal response to the crisis. They joined with environmental and legal groups to petition the EPA to research the environmental impacts and to sue the city and state to provide safe drinking water. And they won. The judge mandated that thousands of lead pipes be replaced and bottled water be delivered to all citizens. Now several years later, the legal battles continue with criminal charges pending for numerous city and state leaders. Most of the active lead-bearing pipes have been replaced, but even now there is still widespread mistrust surrounding drinking the city water.
A serious problem can result from the overuse of groundwater in coastal regions. Here, there is the potential for salt water to flood into the void where aquifers are drained excessively. This process, which is termed saltwater incursion or saltwater intrusion, happens readily because salt water has a higher density than fresh water, hence the pressure under a column of seawater is greater than the pressure under an equivalent volume of fresh water. This results in flow into freshwater aquifers near the coast. Humans and other mammals cannot process large amounts of sodium in water. Ultimately, it leads to renal (kidney) failure. This is why early explorers who became lost at sea were told not to drink seawater. Likewise, salt water kills crops.
Saltwater incursion can occur in one of three ways, all as a result of over-pumping. The first is large-scale, lateral flow into the coastal aquifer, the second is vertical upward flow, and the third is flow into the aquifer from coastal streams and canals, often forced by tidal movements.
Probably the most well-studied example of saltwater intrusion occurs in south Florida, where development combined with highly irregular precipitation patterns have stressed local aquifers. The Biscayne aquifer is the main source of drinking water in the Miami metropolitan area. The aquifer is unconfined, meaning that it is not overlain by aquitards, i.e., it lies at the surface. This renders the Biscayne sensitive to changes in rainfall, evaporation, and over-pumping. Saltwater intrusion occurs as a wedge underneath the surface with a transitional interface with the overlying Biscayne aquifer.
The history of incursion dates back to the 1900s as defined by the first measured increase in salinity (chloride levels) in the Biscayne aquifer. Construction of drainage canals began in 1909 and this resulted in the further inland intrusion of salt water. Intrusion continued unabated until 1946 when salinity-control structures were constructed to prevent inland, tidal movements of salt water. In the 1960s, a large drainage canal system was constructed as part of the massive development of south Florida.
The canals included flow-control structures to prevent excessive drainage from the canal system. However, the design of the structures led to a lowering of freshwater levels in the Biscayne aquifer, leading in turn to increased saltwater intrusion, especially during drought years. Continued movement of the saltwater lens towards the coast and inland has occurred as the new parts of the aquifer have been developed and others tapped less intensively. As in other coastal regions, saltwater intrusion is an ongoing issue that will require constant monitoring as development continues, and demand on aquifers increases. The potential of saltwater intrusion is one issue behind the development of desalinization technology in arid regions.
Sea level rise will increase salinization of coastal aquifers, especially in areas that are dry or subject to seasonal rainfall variability.
As we have seen, climate change will alter precipitation patterns on a global scale, leading to higher rainfall in some areas and significantly lower rainfall in others.
Superimposed on this will be changes in evaporation, runoff, and soil moisture, which will generally exacerbate droughts in areas where rainfall decreases. Generally speaking, regions that are already dry will not get wetter in the next century, and many will become significantly drier.
Regions that are already wet will often become much wetter in the future. Climate change will act in tandem with stressors on the water sector as a result of population increase. Therefore, climate change will generally render precipitation patterns more unequal than they are today. Further, as stated by the Intergovernmental Panel on Climate Change (IPCC),
The negative impacts of climate change on water resources….will outweigh the positive impacts in all regions of the world. Those places in which precipitation and runoff are projected to decline are likely to derive less overall benefit from freshwater resources. In those places that receive more annual runoff, the benefits of increased water flows are expected to be offset by the adverse effects that greater precipitation variability and changes in seasonal runoff have on water supply, water quality, and risk of flooding. (Intergovernmental Panel on Climate Change)
In more detail, recently observed trends of decreasing precipitation over latitudes 30°N to 10°S are projected to continue. Thus, arid and semi-arid regions in the south-central US, Southern Africa, and the Mediterranean are expected to experience decreasing water supply. In some of these regions, water availability is projected to decrease 10-30% by 2050. The IPCC estimates that two-thirds of the world population could be living underwater stress or water scarcity by 2025.
The areas that are expected to suffer some of the worst consequences of changing precipitation are generally some of the least developed and poorest nations, with some of the highest rates of population growth. This combination will likely lead to significantly reduced groundwater recharge, declining surface water reservoir levels, increase in the frequency of groundwater pollution, and most critically, to rapid declines in per capita water availability.
Increased precipitation intensity, more extreme events, increased runoff, decreased infiltration, increased likelihood of contamination with sewage, fertilizers and farm wastes, less ice and snow storage, and increased droughts even in areas that receive more precipitation all will place burdens on water supplies in the future.
Drought could be one of the most serious consequences of climate change from a human and an economic perspective. On a global scale, droughts will likely lead to losses in revenue from agriculture on the scale of billions of dollars, and worse, force the migration of millions of people in arid regions of the world. Not every country can afford to engineer its way out of drought the way that Southern California has done for the last century.
As we have already seen, drought has plagued civilization for millennia and humans have learned to adapt to areas where water supplies are not plentiful or regular. However, the critical difference today is explosive population growth that is placing much more pressure on water supplies. Combined with projections that parts of the globe will become significantly drier in coming decades, drought will likely be much more of a serious issue in the future than it has in the past.
The following video provides an excellent summary of the global drought problem.
Here, we provide two modern-day case studies of the impacts of drought on water supplies in Australia and China and how these countries are responding to them.
Until 2011, much of Australia was in a decade-long drought, providing a grim picture of what the future possibly holds for the driest continent. The Murray-Darling Basin is the most productive agricultural areas in the country, producing a third of Australia’s food. The basin covers over a million square kilometers, about one-seventh of the whole continent, and includes some 20 rivers, most notably the nominate rivers, the Murray and Darling. The region is generally dry (average precipitation is about 500 mm). The total flow of water carried by the Murray and Darling Basin Rivers is significant compared to other Australian rivers, but the amount is dwarfed by the flow of other river systems with equal drainage areas. Thus, the region is prone to drought, and there have been numerous times in the past when the Murray, and especially the Darling, have completely dried up. The Murray- Darling basin produces wool, cotton, wheat, sheep, cattle, dairy produce, rice, oil-seed, wine, fruit, and vegetables. And three-quarters of Australia's irrigated crops and pastures are grown in the basin. Thus, the rivers are vital to the Australian livelihood.
Between 2006 and 2009, precipitation in the mountains in the eastern part of the drainage area, which supplies nearly 40% of the water to the rivers, was lower than at any historical time. Other parts of the basin had a total rainfall deficit of about 1.5 meters below normal for the period 1996-2008. Overall, warmer temperatures that led to higher evaporation rates exacerbated the impact of the drought. For example, the 1oC warming in the basin area is roughly equivalent to a 10% increase in evaporation.
In recent decades, studies have repeatedly confirmed that the environmental health of the Murray-Darling Basin is in decline. On top of the drought, over-extraction of water as a result of past entitlement system has combined with high salinity levels and overall poor water quality, the growth of blue-green algae, declining wildlife, and land degradation to provide a dismal outlook for the basin.
To preserve the water resources of the Murray-Darling, the Australian government has developed a basin plan with a critical provision: an annual water usage (termed a level of take) from the Murray-Darling rivers of 10,873 gigaliters per year (GL/y) that is environmentally and ecologically sustainable for the long term. This take is a cut of about 2750 gigaliters over current levels and will be instituted over a seven-year period. The government is also setting aside some $6 billion to invest in infrastructure, including upgrades to irrigation systems. The plan, which became law in 2012, divides the basin into different surface water (i.e., rivers and lakes) and groundwater areas and sets goals for water usage by agriculture and communities in each of these areas.
Moreover, these districts will have the right to trade water with one another. Overall, the plan is one of the world’s most forward-thinking water use policies. However, it is turning out to be highly controversial. Environmentalists have charged that the plan is too little, too late, insufficient to ensure continued flow through the basin, and not enough to alter the high salt loads in river waters. Politically, there are also significant issues, with some areas targeted for much more drastic reductions in water use than others. However, the policy has the most serious implications for individuals, especially farmers in areas where the most stringent reductions are slated. Enforcement of the water restrictions will almost certainly cause many farmers to go out of business. You can Google “Murray Darling water” for the latest on how this policy plays out.
China faces some of the most serious water issues on the planet. The problems stem from explosive population growth and an inadequate water supply, which has pitted demand for clean drinking water against the demand for industry and agriculture. So in China, drought and pollution combine to make devastating water problems. To put the problem in context, the country has 20% of the world’s population with less than 8% of its water; in other words, the Chinese per-capita water supply is a quarter of the world average. Half of China’s large cities, including Beijing, face a water shortage.
Superimposed on the overall shortage is a significant disparity in supply with the northern tier of China being significantly more arid and the southern tier being significantly more moist. Just under 50 percent of the population of China lives in the northern tier, and close to 60 percent of cultivated land is also in this area, yet only 14 percent of the country's total water resources are found in the region. Production of grain has gradually shifted from the south of China to the north, exacerbating this problem. As a result, the water table is dropping by 1.5 meters per year in parts of the northern portion of the country.
In all, explosive population growth and rapid industrialization have fueled the demand for water nationwide over the last sixty years with the construction of more than 86,000 reservoirs, drilling of more than four million wells, and development of 580,000 square kilometers of irrigated land that generates 70% of the country's total grain production. Generally, lax Chinese environmental controls have led to some of the worst water quality in the world with widespread pollution. Factories are very often situated on river banks for water supply, yet a shortage of water treatment plants results in about 80% of wastewater bring discharged untreated back into the same rivers it came from, and about 75% of rivers are polluted. Worse, approximately 90% of groundwater in urban areas is polluted. Unfortunately, farmers have no choice but to use contaminated water for their crops. And an estimated 700 million people drink contaminated water every day. In some parts of the country, high incidences of digestive cancers (stomach, esophagus, intestine) have been tied to water pollution.
Mismanagement of water resources is commonplace. Diversion of rivers for industrial purposes and irrigation has caused water shortages in areas that once had a steady water supply. The Yellow River, once a sizeable waterway and source of water for agriculture, has been diverted for irrigation and dries up for increasing portions of the year, in 2010 for more than 200 days. As in many parts of the world, industrial demand for water has trumped demand for agriculture. Even when water remains for agriculture, a large amount is wasted through evaporation. The total lost from canals and irrigation systems is 60-80% of the supply.
The following video discusses the water pollution problem in China. Watch the first 10 minutes or so.
Water shortage presents a major obstacle to growth in China, moreover, pollution is a potential environmental catastrophe. To increase the supply of water to areas in the north of the country, China has developed one of the largest public works projects in the world, the South-North Water Diversion Project. This program is designed to divert water from the Yangtze River in the middle of China to rivers in the northern part of the country. Three major routes are being considered for this project, each consisting of tunnels, canals, and dams. However, the project is extremely expensive and its success is not completely ensured, thus plans remain in limbo. In the meantime, the Chinese government pledged $600 million in 2009 to improve water management and combat contamination problems.
You are certain to hear a lot more in the future about continued attempts to provide safe water for the Chinese population and agriculture, especially in the light of climate change.
In areas that are forced to deal with more regular droughts and less regular rainfall, a number of management strategies will become increasingly vital over the coming decades. In rural areas especially in underdeveloped countries, potential strategies include techniques already being piloted in many places including rainwater storage, household treatment using filters, planting of drought-tolerant crops, and drilling of shallow boreholes or tube wells. As we have already seen, poor and disadvantaged populations in developing nations will bear the brunt of adverse effects of climate change. Yet these nations also have less potential to adapt as a result of limited resources. Thus, developed nations will be under great pressure to help their developing counterparts. Adaptation will be the most difficult for sub-Saharan Africa.
In more developed countries, management strategies include conservation, groundwater recharge, storm-water control and capture, preparation for extreme weather events, diversification of the water supply, and resilience to changes in water quality.
The following video is a great summary of our current water situation and what you can do to help out:
It is likely that many or all of these strategies will be required for populations to adapt to declining water resources. One technology, desalinization, has great potential to provide large quantities of water in arid regions, especially those along coastlines.
My one experience with boogie boarding in Hawaii was a disaster. I got caught in no man's land with 15 feet waves breaking on me and my board around my ankles. It took me five minutes to escape to shore, by which time I had consumed a lot of seawater. I had to take a night flight back to the mainland and all I can say was it was not fun! The largest body of water on Earth is the ocean. Desalinization, the removal of salt from seawater, offers great promise to supply citizens in arid regions in the future to come. Here we explore the technology and potential of this technique.
Water desalinization (often termed desalination) has enormous potential for supplying clean water for drinking as well as for irrigation, especially in regions that are arid or have irregular precipitation and are near the ocean. Desalinization is carried out in a number of ways. The most productive method in terms of the amount of water produced is multi-stage flash distillation (MSFD), which produces over 80% of the global volume of desalinized water today. MSFD is carried out in a plant divided into different units, each with a heat exchanger and a collector for the condensate.
The units or reservoirs are maintained at different temperatures, and critically, also at different pressures. The pressure of each reservoir is determined by the boiling point of water at the temperature of the reservoir (lower temperatures require higher pressure for boiling). A brine-heating unit is positioned near the highest-temperature reservoir. Seawater coming into the plant is pumped from the coldest reservoir towards the hottest reservoir and is gradually heated by water traveling the other side of heat exchangers. When the water is pumped into the brine heater it is heated further, then it is cycled back progressively through the lower temperature stages, returning on the other side of the heat exchangers that warmed it on its entry to the plant. In each of these stages, the water is above the boiling point and is warmer than the water on the other side of the heat exchanger. This water then begins to condense leaving desalinized water and brine, which settles in the reservoir. The key aspect of the technique is that it is extremely energy efficient, as water provides much of the heat to itself. However, there are issues in that the water produced still can have impurities if there isn’t significant treatment before entry into the plant. In addition, the technique leaves a large about of brine that needs to be disposed of (this waste is usually disposed of in the ocean).
There are other desalinization processes that also use distillation for the removal of salt and other chemicals. However, the main alternatives to MSFP are those that use reverse osmosis (RO). RO is the most common process used in desalinization, even though RO desalinization plants currently produce about 15% of desalinated water by volume.
Like MSFD, RO requires significant pretreatment to remove solids and bacteria, and to adjust the pH and chemistry so that products such as calcium carbonate and metal colloids do not form. This is critical in the case of seawater, which contains high amounts of turbidity, and organic materials that can clog RO membranes. RO takes place when water is exposed to pressure as it passes through a membrane. As its name implies, the process is the reverse of osmosis, which is the process whereby solutions separated by a barrier such as a membrane flow from the side with low concentration to that with high concentration. When pressure is applied to the membrane in excess of the osmotic pressure, the fluid will flow from the side with the high concentration to that with the low concentration. In so doing, solutes remain on the membrane and the fluid flows from one side to the other. In RO plants, water passes through a number of membranes before it is pure enough for drinking.
The key factor besides purity in the viability of desalinization to produce large quantities of drinking water and water for irrigation is cost, usually referred to as the cost per volume of drinking water produced. The most significant cost is the construction of the plant, but once developed, the key expense involved in desalinization is that of energy. The increasing price of energy could limit the viability of desalinization in many places.
Desalinization is critical to growth and sustainability in countries in the Middle East, and much of the technology was developed here. Today, Saudi Arabia is the largest producer of desalinized water, followed by the United States. In the US, desalinization plants are focused in California and Florida. Countries such as Australia, with extensive arid regions and highly irregular precipitation, are gearing up to increase the amount of water produced by desalinization. For example, in Australia, investment in desalinization will involve a tripling of the number of plants between 2004 and 2013.
Desalinization technologies have applications beyond seawater. For example, desalinization is applied to treat groundwater in inland areas that are too salty for drinking or for irrigation, for example in the El Paso region of Texas. Desalinization can also be used to treat effluent from sewage treatment plants.
In summary, the future of desalinization is very promising, and this technology will likely play an increasing role in countries that can afford to develop it.
Even in regions where desalinization has the potential to add water and strict management practices are underway, water is such a vital commodity that water rights of communities, cities, and even states are often contested in court. Such legal battles sometimes stem from old agreements about the distribution of rivers and groundwater between municipalities that were drawn up before substantial growth occurred. With population growth requiring water for drinking, domestic use, agriculture, and industry, the value of water has increased substantially, and old agreements are often extremely prohibitive to growth. Some of the most bitter water disputes occur in the western US, where, as we have seen, southern California relies heavily on water derived via aqueducts from the Colorado River to the east and the Owens Valley in the Sierra Nevada Mountains to the north.
The City of Los Angeles has had brutal showdowns with farmers and environmentalists in the Owens Valley, from where it derives about half of its water. The city built the first of two aqueducts from the valley between 1908 and 1913 and the second in 1970. These aqueducts substantially lowered water levels in Mono and Owens Lake and the Owens River and took a terrible toll on farming in the Owens Valley. The impact was so negative that farmers used dynamite to breach the aqueduct and temporarily return the flow to the Owens River. After the second aqueduct was built, a series of litigation began between municipalities in the Owens Valley and ultimately the Sierra Club. The net result has been rulings in favor of the Owens Valley, and some increases in water levels in bodies such as Mono Lake, but ultimately southern California continues to withdraw water at a faster rate than it is being replenished, so the conflict is by no means over.
To the east of Los Angeles, water rights for the Colorado River were defined by the Colorado River Compact of 1922, which divided states bordering the river into upper basin states (in the Rocky Mountains) and lower basin states (in the plains to the west). The compact appropriated the annual amount of water each group of states could withdraw from the river with the upper basin states receiving the same amount as the lower basin states.
Today forty million people from Wyoming to Mexico receive water from the Colorado River, so the river is vital to communities small and large and for residential and agricultural use. Since the compact was developed, the lower basin states (Arizona, California, Nevada) have developed especially rapidly and now use a lot more water than they did in 1922. Cities such as Phoenix and Las Vegas have experienced some of the most rapid growth in the country.
The compact was modified when the Hoover Dam was constructed, at which time the lower basin states were allocated annual withdrawal amounts. These amounts have led to fierce litigation between Arizona and California, which changed the appropriations in Arizona’s favor. For a long time, only California has completely utilized its quota each year and its surplus was guaranteed by the Secretary of the Interior until 2016. By that time, surging development in Arizona and southern Nevada required full use of their quotas from the Colorado so that the surplus was no longer available to California.
Two major reservoirs exist in the lower Colorado River basin, Lake Mead and Lake Powell, bounded by the Hoover Dam and the Glenn Canyon Dam, respectively. These reservoirs were designed for water management, but both have been drying up recently. The situation is dire in both reservoirs, as the images below show. Let’s start with Lake Powell. This reservoir provides water and electricity generated through turbines in the Glen Canyon Dam to millions of people. The level in Lake Powell is lower than it has ever been. As of June 2023, the level was at 3580 feet with the normal level being 3700 feet. If the level drops below 3490 feet (a level known as “dead pool”), water cannot flow downstream to the lower basin states from the reservoir. In addition, the dam would not be able to generate electricity, potentially cutting off power to millions.
Lake Mead’s issues may be even more pressing, as the lake provides 90 percent of nearby Las Vegas’s water. The largest reservoir in the country had a level of 1049 feet in May 2022 which was 170 feet below the maximum capacity. The level was so low that sunken boats resurfaced and an intake valve (for pumping to Las Vegas and other communities) was exposed. Las Vegas was taking water from the lower intake valves, which were installed to retrieve water at lower lake levels. Fortunately, there was a massive amount of snow in the mountains in the winter of 2022-2023 and the level has risen somewhat. But regardless, Las Vegas is planning for a future when low water supply is the new normal and frequent dead pool” events when no water flows out of Lake Mead. Fortunately, a third intake valve and pumping station for Las Vegas’s water has been installed below the dead pool level, so the city will still receive water, but the city is already imposing severe water restrictions including banning grass in yards and strictly limiting watering of grass on golf courses. The city also recycles a lot of its water. These and other measures have been successful in reducing the demand for water: over the last twenty years the population has grown by 49% but water use has shrunk by 26%. Regardless, the future looks bleak as the decades long drought in the area is forecasted to continue.
So, the situation is dire for both Lake Mead and Lake Powell, and recently in 2023 the US government brokered a temporary deal whereby the lower basin states (California, Arizona and Nevada) must lower their water extraction from the Colorado by 13 percent. However, a longer term deal must be reached by 2027 and this will likely involve some tough negotiation. Essentially, the original 1922 compact was developed at a very wet time in the west, and the upper basin states (Colorado, Wyoming and New Mexico) can’t afford to give 50% of the water to the lower basin states when they need the water to fuel growth in cities such as Denver and Albuquerque as well as provide the water farmers and ranchers desperately need.
A sign of the times to come, Phoenix just imposed restrictions on development in the fastest growing suburbs where the supply comes from groundwater. The new rules say that no new development can take place without an alternate source of surface or recycled water. Such controls are likely in all of the southwestern cities in the future as climate change leads to even lower water supplies.
In this module, you should have learned the following concepts:
You should have read the contents of this module carefully, completed and submitted any labs, the Yellowdig Entry and Reply and taken the Module Quiz. If you have not done so already, please do so before moving on to the next module. Incomplete assignments will negatively impact your final grade.
Links
[1] https://www.youtube.com/channel/UCU1QB1a5XJa_nTHD2lzr7Ew?feature=emb_ch_name_ex
[2] http://water.org/
[3] https://www.e-education.psu.edu/earth103/node/889
[4] https://creativecommons.org/licenses/by-nc-sa/4.0/
[5] https://www.youtube.com/channel/UC8SgBnHvY8wzrX3c0VcHfFg?feature=emb_ch_name_ex
[6] https://www.youtube.com/channel/UCU1QB1a5XJa_nTHD2lzr7Ew
[7] https://www.e-education.psu.edu/earth103/sites/www.e-education.psu.edu.earth103/files/Lab%208.docx
[8] https://waterwatch.usgs.gov/index.php?id=ww_animation
[9] http://www.solpass.org/
[10] https://kunden.dwd.de/GPCC/Visualizer
[11] http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ENSO/composites/EC_LNP_index.shtml
[12] https://www.e-education.psu.edu/earth103/sites/www.e-education.psu.edu.earth103/files/module08/MississippiStreamGagesUpdated.kmz
[13] https://water.usgs.gov/edu/earthgwaquifer.html
[14] http://www.co.pepin.wi.us/
[15] https://www.flickr.com/photos/golf_pictures/
[16] https://www.flickr.com/photos/golf_pictures/5111143657/
[17] https://creativecommons.org/licenses/by/2.0/
[18] https://www.youtube.com/channel/UC5O114-PQNYkurlTg6hekZw?feature=emb_ch_name_ex
[19] http://www.groundwateruk.org/Image-Gallery.aspx
[20] https://creativecommons.org/share-your-work/public-domain/cc0/
[21] https://www.youtube.com/channel/UCXzicKpfSXa90q54SE6Nx5Q?feature=emb_ch_name_ex
[22] https://www.youtube.com/channel/UCV3Nm3T-XAgVhKH9jT0ViRg
[23] https://www.usgs.gov/
[24] http://www.flickr.com/photos/jaxstrong/
[25] https://www.youtube.com/channel/UCqTDtf5WMrE7z8JCK_FrKAg?feature=emb_ch_name_ex
[26] http://www.mdba.gov.au/
[27] http://www.nswfarmers.org.au/
[28] https://factsanddetails.com/china/cat10/sub64/item399.html#chapter-6
[29] https://www.youtube.com/channel/UCF8Uhj557ROtKoMm8xdZyKA?feature=emb_ch_name_ex
[30] https://www.youtube.com/channel/UCHXPqS4M2OcOUGYEtPM3CxQ?feature=emb_ch_name_ex
[31] https://www.youtube.com/channel/UCdw3GhAw0c7oPeTDV5gn6Zg?feature=emb_ch_name_ex
[32] https://commons.wikimedia.org/wiki/User:Chrkl
[33] http://en.wikipedia.org/wiki/Reverse_osmosis
[34] https://creativecommons.org/licenses/by-sa/3.0
[35] https://www.youtube.com/watch?v=5CADLfXOhkU
[36] https://www.youtube.com/@VICENews
[37] http://earthobservatory.nasa.gov/Features/WorldOfChange/lake_powell.php