Download
1 / 19
250 likes | 506 Vues
Water resources chapter 13. Peyton Adams. Will we have enough usable water?. We are using available freshwater unsustainably by wasting it, and charging too little for this irreplaceable natural resource.
E N D
Water resourceschapter 13 Peyton Adams
Will we have enough usable water? • We are using available freshwater unsustainably by wasting it, and charging too little for this irreplaceable natural resource. • One of every six people does not have sufficient access to clean water, and this situation is likely to get worse. • Saltwater covers 71% of the earths surface • Water is irreplaceable, we can only survive a few days without water. • It takes large amounts of water to supply us with food, energy, and most other things that we use to meet our daily needs and wants. • Despite its importance, water is one of our most poorly managed resources. We waste and pollute water. • 3,900 children younger than the age of 5 die from waterborne infectious diseases because they do not have access to safe drinking water. • Water is an economic issue because it is vital for reducing poverty and producing food and energy. • Almost half of the worlds people do not have access to water in their homes, so they have to get some from nearby wells. • Water is an environmental issue because excessive withdraw of water from rivers and aquifers results in falling water tables, decreasing river flows, shrinking lakes, and disappearing wetlands.
Most of the earths freshwater is not available to us. • About 0.024% of the planets enormous water supply is available to us in groundwater deposits and in lakes, rivers, and streams. The rest is in salty oceans, frozen polar ice caps/ glaciers, and deep underground, in inaccessible locations. • The worlds water supply is continually collected, purified, recycled and distributed in the earths hydrologic cycle (the movement of water in the seas, air, and on land, which is driven by solar energy and gravity). • This irreplaceable water recycling and purification system works well, unless we overload it with pollutants or withdraw water from under ground and surface water supplies faster than it can be replenished. • We can also alter precipitation rates and distribution patterns of water through our influence on projected climate change. In some parts of the world, we are doing all these things, mostly because we have thought of the earths water as essentially a free and infinite resource. • On a global basis, we have plenty of freshwater, but it is not distributed evenly. • Canada has 20% of the worlds liquid freshwater, China has 7% of the worlds supply, and Asia has 30% of the water supply.
Water shortages will grow • The main factors that cause water scarcity in any particular area are a dry climate, drought, too many people using a water supply more quickly than it can be replenished, and wasteful use of water. • More than 30 countries now face stress from water scarcity. • 30% of the earths land area experiences drought. • By 2059, as much as 45% of the earths land surface could experience extreme drought. • Two or more countries share the available water supplies in each of 263 of the worlds water basins, which together cover nearly half of the earths surface and are home to about 40% of the worlds people.
There are several ways to increase freshwater supplies • We can provide more water by reducing unnecessary waste of water. • Other solutions involve increasing water supplies by withdrawing groundwater, building dams and reservoirs to store runoff in rivers for release as needed, transporting surface water from one area to another, and converting saltwater to freshwater.
Is extracting groundwater the answer? • Groundwater used to supply cities and grow food is being pumped from aquifers in some areas faster than it is renewed by precipitation. • Aquifers provide drinking water for nearly half of the worlds people. • In the US, aquifers supply almost all of the drinking water in rural areas, one fifth of that in urban areas, and 37% of the country's irrigation water. • More than 400 million people, including 175 million in India and 130 million in China, are being fed by grain produced through this unsustainable use of groundwater, according to the world bank. This number is expected to grow until the water runs out or until governments put caps on aquifer withdrawal rates and stop providing subsidies that encourage over pumping and water waste.
Advantages and disadvantages of withdrawing groundwater Advantages Disadvantages • Useful for drinking and irrigation. • Exists almost everywhere. • Renewable if not over pumped or contaminated. • Cheaper to extract than most surface waters. • Aquifer depletion from over pumping. • Sinking of land from over pumping. • Pollution of aquifers lasts decades of centuries • Deeper wells are nonrenewable.
Aquifer depletion in the United States • In the US, groundwater is being withdrawn from aquifers, on average, four times faster than it is replenished. • One of the most serious overdrafts of groundwater in in the lower half of the Ogallala, the worlds largest known aquifer, which lies under eight Midwestern states from southern South Dakota to Texas. • The problem with the Ogallala is that it is essentially a one time deposit of liquid natural capital with a very slow rate of recharge. • The Ogallala helps to support biodiversity.
Groundwater Depletion Prevention Control • Waste less water • Subsidize water conservation • Limit number of wells • Do not grow water intensive crops in dry areas. • Raise price of water to discourage waste • Tax water pumped from wells near surface waters • Set and enforce minimum stream flow levels • Divert surface water in wet years to recharge aquifers.
Is building more dams the answer? • A dam is a structure built across a river to control the rivers flow. • Usually, dammed water creates an artificial lake (reservoir), behind the dam. • The main goals of a dam and reservoir are to capture and store runoff, and release it as needed to control floods, generate electricity, and supply water for irrigation and for towns and cities. • Reservoirs also provide recreational activities such as swimming, fishing, and boating.
Advantages and disadvantages of building dams Advantages Disadvantages • Provides irrigation water above and below dam. • Provides water for drinking • Reservoir useful for recreation and fishing • Can produce cheap electricity • Reduces downstream flooding of cities and farms. • Flooded land destroys forests or cropland and displaces people • Large losses of water through evaporation • Deprives downstream cropland and estuaries of nutrient rich silt • Risk of failure and devastating downstream flooding • Disrupts migration and spawning of some fish.
Is transferring water from one place to another the answer? • Transferring water from one place to another has greatly increased water supplies in some areas but has also distributed ecosystems. • Using a lot of water to produce a particular type of food or other product is not necessarily bad if it is done n an area where water is plentiful and water waste is controlled. • Water waste is part of the reason why many products include large amounts of virtual water. • One factor contributing to inefficient water use- for example, growing thirsty lettuce in desert like areas- is that governments subsidize the costs of water transfers and irrigation in some dry regions. Without such subsidies, farmers could not make a living in these areas.
Case study California transfers massive amounts of water from water rich areas to water poor areas The Aral sea disaster: a striking example of unintended consequences. • One of the worlds largest transfer projects is the California Water Project. It uses a maze of giant dams, pumps, and lined canals to transport water from water rich northern California, to water poor southern California's heavily populated cities and agricultural regions. This project supplies massive amounts of water to areas that, without such water transfers, would be mostly desert. • The shrinking of the Aral sea, once a large inland body of saline water, is the result of a large scale water transfer project in an area of the former soviet union with the driest climate in central Asia. Since 1960, enormous amounts of irrigation water have been diverted from the two rivers that supply water to the Aral Sea. The goal was to create one of the worlds largest irrigated areas, mostly for raising cotton and rice.
Is converting salty seawater to freshwater the answer? • We can convert ocean water into freshwater, but the cost is high, and the resulting salty brine must be disposed of without harming aquatic or terrestrial ecosystems. • Desalination involves removing dissolved salts from ocean water or from brackish water in aquifers or lakes. • The two most widely used methods for desalinating water are distillation (heating saltwater until it evaporates) and reverse osmosis (uses high pressure to force saltwater through a membrane filter with pores small enough to remove the salt). • There are three major problems with the widespread use of desalination. 1) there is a high cost, 2) pumping large volumes of sea water through pipes and using chemicals to sterilize the water kills marine organisms and requires large amounts of energy, and 3) this produces huge quantities of salty wastewater that must go somewhere.
Reducing water waste has many benefits • Some benefits of reducing wastewater are about two thirds of the water throughout the world is unnecessarily wasted through evaporation, leaks, and other losses. • In the US, about half of the water drawn from surface and groundwater supplies is unnecessarily wasted. It is economically and technically feasible to reduce water waste to 15%, thereby meeting most of the worlds water needs for the foreseeable future. • A basic rule of economics is that you get more of what you reward. Withdrawing environmentally harmful subsidies that encourage water waste and providing environmentally beneficial subsidies for more efficient water use would sharply reduce water waste and help to reduce water shortages.
Solutions to… Reducing irrigation water waste Reducing water waste • Line canals bringing water to irrigation ditches. • Irrigate at night to reduce evaporation • Monitor soil moisture to add water only when necessary • Grow several crops on each plot of land • Encourage organic farming • Avoid growing water thirsty crops in dry areas • Irrigate with treated waste water • Import water intensive crops and meat • Redesign manufacturing processes to use less water • Recycle water in industry • Landscape yards with plants that require little water • Use drip irrigation • Fix water leaks • Use water meters • Raise water prices • Use waterless composing toilets • Require water conservation in water short cities • Use water saving toilets, showerheads, and front loading clothes washers. • Collect and reuse household water to irrigate laws and nonedible plants • Purify and reuse water for houses, apartments, and office buildings.
Some areas get too much water from flooding • Some areas have too little water, but others sometimes have too much because of natural flooding by streams, caused mostly by heavy rain r rapidly melting snow. • A flood happens when water in a stream overflows its normal channel and spills into an adjacent area, called a floodplain. • These areas, which usually include highly productive wetlands, help to provide natural flood and erosion control, maintain high water quality, and recharge groundwater. • Floods kill thousands of people each year and cost tens of billions of thousands of dollars in property damage. • Floods are usually considered natural disasters, but since the 1960s, human activities have contributed to a sharp rise in flood deaths and damages, meaning that such disasters are partly human made.
Solutions to reducing flood damage • Preserve forests on watersheds • Preserve and restore wetlands in floodplains • Tax development on floodplains • Use floodplains primarily for recharging aquifers, sustainable agriculture and forestry. • Straighten and deepen streams • Build levees or floodwalls along streams • Build dams.
Big ideas of the chapter • One of the worlds major environmental problems is the growing shortage of freshwater in many parts of the world. • We can increase water supplies in water short areas in a number of ways, but the most important way is to reduce overall water use and waste by using water more sustainably. • We can use water more sustainably by cutting water waste, raising water prices, slowing population growth, and protecting aquifers, forests, and other ecosystems that store and release water.
