Tectonic plates • Definition o They are the crusts that float on the mantle Plate tectonics • Definition o The process by which the crustal plates are being moved by convection currents • How does plate moves? o The force that brings about the motion of the crustal plates comes from the tremendous heat found in the Earth’s interior o This heat causes the rocks in the mantle to melt and become molten rocks called magma o When magma is heated, it expands rises and generates convection currents, which push the plates away from each other o When it cools, the magma sinks and brings the plates towards each other o This constant rising and sinking of the magma results in the movement of the plates over the Earth’s surface Plate movements • Types o Divergent plate movement o Convergent plate movement o Transform plate movement • Divergent plate movement o Constructive plate boundaries o Tensional force o Oceanic-oceanic crusts Ridges (Mid-Atlantic Ridge) Lava fountains in the middle of ridges o Continental-continental crusts Rift valleys (East African Rift Valley) Magma rises and squeezes through the widening cracks, sometimes to erupt and form volcanoes The rising magma puts more pressure on the crust to produce additional fractures and, ultimately, the rift zone • Convergent plate movement o Destructive plate boundaries o Compressional force o Oceanic-continental crusts Mountains (Andes) Trench (Peru–Chile Trench) Earthquakes o Oceanic-oceanic crusts Oceanic trenches (Marianas Trench) Volcanic islands island arcs (Hawaiian Islands) Earthquakes o Continental-continental crusts Fold mountains (Himalayas) • Transform plate movement
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Conservative plate boundaries Frictional force Fault lines (St Andreas Fault, San Francisco) Earthquakes
Formation of Mid-Atlantic Ridge o Divergent plate movement causes fractures and cracks to develop at the plate boundary o Magma from the mantle begins to flow out from the cracks o When this magma solidifies, new crust is formed at the plate boundary o The constant flow magma along the Mid-Atlantic Ridge causes new crusts to form continuously and the old crust to be pushed further and further away from the plate boundary • Subduction, fold mountains, volcanoes, and trenches in oceaniccontinental convergent plate movement o Subduction When an oceanic plate collides with a continental plate, the thin and dense oceanic plate will bend underneath the thicker but less dense continental plate Gradually, the oceanic plate is pushed down into the depth of the molten upper mantle where it is melted into molten rock. o Fold mountains The less dense continental plate moves over the denser oceanic plate The crusts at the plate boundary gradually folds, rises and crumples to form fold mountains o Volcanoes The crust eventually melts as it moves deeper into the hot mantle Magma is formed, which due to its lower density, rises to the surface, leading to volcanic eruptions It is therefore quite common to find active volcanoes where convergent plate movement takes place Definition • A mountain or a hill formed of materials from the Earth’s interior that have been ejected under pressure from a vent o Trench Definition • The oceanic plate is subducted forming a depression, which is a trench • Trenches, earthquakes and volcanic island arcs in oceanic-oceanic convergent plate movement o Trench Definition • The convergence of two oceanic plates usually results in one being subducted under the other, leaving a depression, known as a trench o Earthquakes
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Moderate to strong earthquakes are also frequent due to the stress created by the interaction of the two plates Volcanic island arcs Volcanoes also result from the subduction process The continuous eruption of lava and volcanic debris along the subduction zone accumulates on the ocean floor Over millions of years, the resultant undersea volcanoes rise to form volcanic island arcs Fold mountains in continental-continental convergent plate Fold mountains Subduction does not take place, as continental rocks are relatively light The crust may be folded at the collision zone to form spectacular overland mountain ranges Found along convergent plate boundaries where two plates collide Fault lines and earthquakes in transform plate movement Definition Lateral movement of the plates as they slide past each other Fault lines Boundaries where such plate movements take place are known as transform fault margins Earthquakes At the transform plate margins, huge landmasses moving in opposite directions result in tremendous friction and give rise to earthquakes
Description o When two plates collide, the compressional force puts the rock layers that form the Earth’s crust under great pressure o Eventually, the bend and fold Where o Usually found in sedimentary rocks because these rocks are softer and more flexible than other types of rocks Why o Have the ability to deform under pressure o Folding found along convergent plate boundaries where two plates collide Process o When plates move, parts of the Earth’s crust may be subjected to compressional force or tensional force, which pulls the Earth’s crust apart o These forces can cause the crust to fracture or tear apart o The type of rock is a key factor that determines whether the rock will respond to pressure by folding or faulting
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o While folding tends to be common in sedimentary rocks because of their flexibility, faulting is common in rocks that are brittle such as igneous and metamorphic rocks o These rocks tend to fracture and break under pressure o Unlike folding which tends to release stress gradually, faulting tends to store up stress and then release it suddenly o This may result in earthquakes Tensional force o A-shaped Block mountain (rises) o V-shaped Rift valley (lowers) Compressional force o A-shaped Rift valley (lowers) o V-shaped Block mountain (rises) Normal faulting o Caused by tension o One block is lowered relative to adjacent block Reverse faulting o Caused by compression o One block rises relative to the adjacent block, forming an overhanging escarpment o The overhanging escarpment will be weathered and would disappear over time, forming a steep slope Block mountain o A raised block of land that has been uplifted or left standing after the surrounding areas have sunk during faulting o Initially, a block mountain will have steep sides and a flat top o Erosion and weathering may reduce it to a range of rounded hills over time o The distribution of uplifted block mountains can be found along fault lines caused by either compression or tension Rift valley o Occurs when the central block of land between two parallel faults sinks o The rising convection currents that pull the two plates apart also produce volcanoes in the rift valley
Vulcanicity • Definition • Another major tectonic process • The upward movement of magma to the Earth’s surface forms volcanoes over time • Volcanoes are usually found along or near the plate boundaries • Generally, a volcano is built up by the emission of lava and ashes from a vent in the Earth’s crust • Classification of volcanoes • By frequency of eruption
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Active volcano Constant emission of lava, ash, dust and smoke Strong sulfur smell Dormant volcano Has not erupted for hundreds of years May erupt any time in the future Extinct volcano Has no record of eruption in recorded history No sign of possible eruption
Shield volcano (Mauna Loa, Hawaii) Cone-shaped with gentle slopes Consists of many layers of lava due to repeated flows Hot and fluid basic lava flows from a central vent Spreads over a wide area Cools and solidifies slowly Frequent eruptions but usually quiet and gentle with large quantities of fluid basic lava Acid lava dome volcano (Mt. Mayon, Philippines) Done-shaped with steep convex slopes Viscous acidic lava flows from a central vent Cools and solidifies quickly Lava may even cool and solidify as it flows up the vent When lava solidifies and blocks the vent, gases, and pressure, build up inside the volcano A massive and violent explosion may occur The entire top of a volcano may be blown off Composite volcano (Mt. St Helens, USA) Large and con-shaped, with steep slopes Alternate eruptions of viscous acidic lava, ash and cinder Creates violent explosions Lava may escape through the sides of the cone
Basic Low viscosity (very fluid) Low silica content High temperature Flows readily o Acidic High viscosity (not very fluid) High silica content Low temperature Flows slowly Formation of volcanoes o Composite volcano Viscous lava solidifying in the central pipe Gas pressure builds up as magma cannot escape When pressure cannot be suppressed, eruption occurs Ash and cinders thrown into the air falls back near vent Lava flows over the ash and cinders
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Repeated eruptions form alternating layers of ash and cinders and lava. o Shield volcano Basic lava is less viscous Hence spreads over a large area before solidifying o Acid lava dome volcano Acid lava is more viscous Hence cools quickly before it can travel far Other possible extrusive features o Caldera Definition • An enlarged crater o Formation Collapse of volcano into magma chamber Eruption of volcano o Crater lakes Definition Crater filled with water o Formation Rainwater filling up crater and empty magma chamber over years Usefulness of volcanoes o Fertile volcanic soils o Valuable minerals and precious stones are found in volcanic rocks o Interesting volcanic landforms can lead to the development of the tourism industry, which is an important source of revenue o Geothermal energy is an important source of clean energy for generating electricity
Earthquake LORMS • Use of technology to prevent fire hazards o Fire is commonly seen after earthquakes as gas pipes are ruptured by the stress the earthquakes put on the pipes. With live wires going across the whole city, the leaking gases are easily ignited causing a fire, which could possibly cause more damage. o One way to prevent this is to install systems capable of detecting earthquakes, which would then cut supply of gas in the pipes and electricity in the wires to the affected area minimizing the chances of fire. o This method is successful because it minimizes the chance of a fire and thus reduces loss of life and damage to property. o This method is limited because it may be expensive to implement because of the fact that these systems would have to be installed all over the city. • Construct earthquake-resistant buildings o In areas with frequent earthquakes, buildings can be constructed to meet the earthquake-resistance standards. High-rise buildings should have flexible frames, while smaller buildings should have concrete frames with reinforcing bars to absorb the impact of earthquakes. The foundations of tall buildings should be built on solid
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bedrock rather than loose materials such as clayey soil. Fire-resistant materials can also be used to construct the buildings. o The Transamerica Pyramid Building in San Francisco has been built to withstand tremors caused by earthquakes with steel bars and deeper foundations. o This has been very successful as proven by the 1989 San Francisco Bay earthquake registering 7.1 on the Richter scale. Not only no one was hurt, there was minimum damage suffered by the building. o This method is limited because of the cost involved to have reinforcing structures. It is also impossible to add this reinforcement into the buildings that are already standing. Use of technology to predict and monitor tectonic activities o Advanced technology can be used to carry out earthquake prediction more accurately. Scientists estimate earthquake probabilities though a number of ways. Accurate predictions and monitoring provide crucial information so that people living in affected areas can be warned. These people can then be evacuated before a disaster strikes. o One way is to study the history of massive earthquakes in a specific area to determine the likelihood of such earthquakes reoccurring. o The success of this method is people can be pre-removed from the affected area and would not be part of the victims, so the loss of life would not be so serious. o The limitation is that this method is highly expensive and developing countries may not be able to afford for the advanced technology required to predict earthquakes.
Weather • o o o Climate • o
Definition The conditions in the atmosphere of a particular area at a particular point in time Short-term condition of the atmosphere Changes all the time and varies from place to place
Definition Average weather conditions over a long period of time (at least 30 years)
Factors affecting temperature • Latitude o Due to the spherical shape of the Earth, the Sun’s rays strike different parts of the Earth’s surface at different angles o Results in unequal distribution of solar energy over the Earth’s surface o The nearer a place is to the Equator, the more direct the sunlight it receives o At higher latitudes, the same amount of solar radiation is spread over a wider area, resulting in lower temperatures o The Equator receives the Sun’s rays at a high angle of incidence which causes the Sun’s rays to be concentrated in a smaller area, giving the area more intense sunlight and higher temperatures
Towards the Poles, the Sun’s rays strike at smaller angles of incidence. Hence, temperatures decrease accordingly. Altitude o The sun’s rays heat the Earth’s surface, which then passes on its heat to the atmosphere o The layer of air nearest to the Earth’s surface is heated up first, and so the atmosphere will be heated from the ground up o This explains why there is a drop in temperature with increased altitude o Moreover, gravity pulls everything towards the Earth’s surface, including air molecules o As a result, air is densest at sea level and less dense at higher altitudes o With less air to absorb heat at higher altitudes, temperatures drop as altitude increases Maritime and continental influences o The land and sea heat up at different rates o The land absorbs and loses heat faster than the sea because heat from the Sun does not penetrate land surfaces as deeply as they penetrate bodies of water o Therefore, seas and oceans take a longer time to heat up, and once heated up, they also retain the heat longer o Land, on the other hand, heats up very quickly and loses heat quickly too o Two cities in temperate regions may be located along the same latitude, thus experiencing similar angle of incidence of the Sun and similar length of daylight in winter o However, the one located farther inland will experience lower temperatures than the one located along the coast because the temperatures along the coast are being moderated by the influence of the sea o The warmer sea in winter helps to prevent the temperatures along the coastal area from dropping too low o In summer, the reverse is true o The land in summer gets heated up much faster and becomes much warmer than the sea o Cities that are located far inland are not able to experience the moderating influence of the cooler sea, thus their temperatures are higher than cities along the coast which, which the influence of the cooler sea, record lower summer temperatures Cloud cover o In the day, cloud cover helps to reflect a significant portion of solar radiation back to outer space o This reduces the amount of incoming solar radiation o Therefore, the daytime temperature is lower when there is cloud cover and higher when the sky is clear o Cloud cover at night as a blanket that prevents heat from escaping from the Earth’s surface o It absorbs and then re-emits part of the radiated heat back to Earth o As a result, temperatures on a cloudy night do not drop as low as temperatures on a clear night o
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Relative humidity • Definition o The ratio of the actual amount of water vapor in the air compared with the maximum amount of water vapor that a unit of air can hold at that temperature • Effects of temperature o As the temperature increases, the amount of water vapor the air can hold also increases and the relative humidity falls o When the temperature drops, the relative humidity increases because the air has less capacity to hold water vapor o This is why during the day, when the temperature is high, relative humidity tends to be low while at night when the temperature decreases, relative humidity increases • Saturation point o Definition The point where the air can no longer absorb any more water vapor • Dew point o Definition The temperature at which the saturation point is reached Rainfall • Types of rain o Convectional rain o Relief rain • Formation of convectional rain o During summer, the Earth’s surface becomes very hot o Intense warming of the air air rises quickly o Air expands and cools o Condensation takes place rainfall o The cool air then falls and is caught and dragged back upwards by more rising air, forming a convection cell • Formation of relief rain o Occurs when air is forced to rise over physical barriers such as a mountain range o Parcels of moist air coming in from the sea are forced to rise as they encounter a tall mountain range running along the coast o As the parcels of air are lifted up, cooling takes place o Eventually, condensation occurs which followed by heavy rainfall o Clouds form mainly on the side of the mountain range facing the incoming wind where the air parcels are forced to rise o This side of the mountain range receives most of the rain and is known as the windward side o By the time the winds pass over the mountain range, the winds have lost most of their moisture o This side of the mountain receives little or no rain, and is known as the leeward side Air pressure • Definition
The force exerted on a unit area of the Earth’s surface by the weight of a column of air above it Factors o Temperature The higher the temperature, the greater the air expansion, the lower the pressure The lower the temperature, the smaller the air expansion, the higher the pressure o Density The less dense the air, the lower the pressure The denser the air, the higher the pressure o Altitude The higher the altitude, the less dense the air, the lower the pressure The lower the altitude, the denser the air, the higher the pressure Local winds o Types of local winds Land breeze Sea breeze o Land breeze During the night, the land cools down much faster than the sea This creates an area of higher pressure over the land The cooler and denser air from the land begins to move towards the sea to replace the warmer and lighter air over the sea o Sea breeze During the day, air over the land is heated up more rapidly than the air over the sea As warm air rises, a low pressure area is formed Air over the sea, however, is cooler because the sea is heated up more slowly This cooler air, which is denser sinks Hence, air pressure is high over the sea This causes wind to blow from the sea towards the land, lowering temperatures along the coast Regional winds o Types of regional winds Monsoon winds o Monsoon winds In December, Central Asia experiences winter which results in lower temperatures and thus, a high pressure zone In Australia at the same time, Australia experiences summer, which results in higher temperatures and thus, a low pressure zone Winds travel from a higher pressure zone to a lower pressure zone Due to the Coriolis Effect, which deflects the winds to the right in the Northern Hemisphere, and after passing the equator, the winds are deflected to the left and on to Australia, the winds travels from Central Asia towards Malaysia through the South China Sea o
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In the South China Sea, the winds collect a lot of moisture and bring the moisture to Malaysia Once at Malaysia, the moisture falls back to the Earth as rain, as the winds collected a lot of moisture, a heavy downpour is experienced in Malaysia in December This is called the Northeast Monsoon because the winds came from the northeast In June, Australia experiences winter which results in lower temperatures and a high pressure zone Central Asia experiences summer which results in higher temperatures and a low pressure zone Winds travels from the high pressure zone to the low pressure zone Due to the Coriolis Effect, the winds are deflected to the left in the Southern Hemisphere, as it goes into the Northern Hemisphere , the winds are deflected to the right, the winds therefore travel through the Indian Ocean, collecting moisture as it travels towards Malaysia Due to the fact the winds need to travel through Indonesia, the moisture is lost in the form of rain in Indonesia, there is only minimal rain in Malaysia This is known as the Southwest Monsoon as the winds came from the southwest
Causes of flooding in Bangladesh • Drainage of land o Bangladesh is a land of many river channels o These rivers, the Ganges, the Brahmaputra and the Meghna, enter the Bay of Bengal through Bangladesh o Every year, with the onslaught of the Southwest Monsoon and resultant frequent heavy rain, the water levels in these rivers will naturally rise, leading to floods • Relief of land o Bangladesh is a low-lying country o Most of the land is below 10m above sea level • Snow melt from the Himalayas Mountains o During summer time, when the snow melts, the melt water flows in the Ganges and Brahmaputra rivers o With the increased in volume of water in these rivers, river flooding is common • Storm surge o The strong winds that bring about tropical storms can create a storm surge o This brings massive floods that could destroy coastal settlements Effects of flooding in Bangladesh • Social impact o Loss of lives Sudden floods brought about by giant waves that accompany tropical storms or that are caused by the failure of dams often catch people by surprise
With little or no time for the people to be evacuated, they could be swept away by the fast flowing water or be drowned by the rapid rise in water levels o Loss of property Floods also damage or destroy property such as houses and farmlands and damage infrastructure such as roads, electricity and communication lines Thousands of people could be left without shelter when their homes are swept away or destroyed by flood waters The loss of agricultural fields could also cause a shortage of food supply, which would lead to starvation and even famine o Contamination of water supply There may be a shortage of fresh water when rising waters submerge wells Contamination of water also occurs when flood waters carry sewage which is then mixed with the fresh water supply o Spread of diseases The stagnation of water could bring about water-borne diseases such as cholera and dysentery These diseases may spread and become an epidemic, affecting public health and endangering lives Economic impact o Accumulation of debt Flood-related damages to public and private property may amount to millions of dollars Less developed countries that are devastated by floods are unlikely to possess the huge amount of funds that is needed for repair works Borrowing from international agencies could plunge these countries into further debt that may not be able to repay This, in turn, will slow down their economic development o Slowdown of economy Floods may also damage agricultural fields and reduce crop production Countries that depend on the agricultural sectors to sup[port their economies may lose their main source of income Environmental impact o Soil erosion The rush of water brought by floods may cause soil erosion, especially in areas where the vegetation has been cleared As a result, the topsoil may be eroded away, leaving the soil less fertile than before o Waterlogged conditions Floodwaters could be retained in particular areas that have soils that do not allow water to pass through easily Being waterlogged leaves the land unsuitable for purposeful uses
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Flooding LORMS • Building flood barriers o One measure to prevent excessive damage from floods is the erection of barriers such as dams, artificial levees, and floodwalls. They help to
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prevent water in rivers from overflowing. In coastal areas, the building of structures such as seawalls, breakwaters and floodgates, fulfill the same purpose. In coastal area where flooding can be caused by storm surges or in some cases by tsunamis due to earthquakes, coastal defenses such as flood barriers are constructed to stop the high waves from crashing into the coastal areas o At the mouth of the River Thames in England, a flood barrier is built across the mouth to protect against floods caused by high tides. o The success of this method is that the effectiveness of a barrier. The barrier has protected London from river flooding repeatedly. o The limitation is that this method may be highly expensive and developing countries may not be able to afford such a protection measure. Ensuring proper urban planning o Proper urban planning is crucial for flood control in urban areas. An effective public information system, close coordination among important agencies and effective power back-up systems are important for minimizing the damage caused by floods. By far, the most effective way to control and prevent widespread damage by floods in an urban area is a good and well-maintained sewerage system. Drains and canals can be widened to accommodate more rainwater, and underwater sewerage systems must be properly maintained to prevent any blockage by rubbish. o Inadequate urban planning led to the high number of deaths in the 2005 Mumbai flood, showing the importance of proper urban planning. o The success is that this method does not require a lot of money and thus is a viable option for developing countries. o The limitation is that even with proper planning, if the plan is not abided to, the amount of planning does not matter. Improving weather forecasting o Better and more precise weather forecasting can improve flood prediction. People can evacuate from their homes before the flood occurs. If they cannot evacuate, at least they can be better prepared when the flood comes. o Accurate weather forecasting allowed the Thames Barrier to be closed way ahead of time and for the media to notify the people in London so they can be prepared for what is to come. o The success is that this method would allow people to evacuate before they are in harm’s way. o The limitation is that this method may be highly expensive, as advanced technology would be needed for accurate weather forecasting.
Causes of droughts • Natural causes of droughts o Shortage of rainfall • Studies on the historical trends of droughts suggest that dry periods occur regularly as part of the Earth’s climatic conditions • They could also occur because of unusual weather conditions that create a shortage of rain in a normally wet area
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This unexpected shortage of rainfall could dry up soil moisture, underground water, rivers and streams, thus resulting in droughts Human causes of droughts o Increase in population • Rapid population growth increases the demand for more land which is needed for agriculture and the building of industries and settlements • Improper agricultural practices to increase food supply may worsen drought situation • When farmers rear more cattle than the land can support, overgrazing occurs and the vegetation is consumed faster than it can be replaced • Another improper practice is when the land is used continuously for growing crops, without allowing it to fallow • The land has little time to recover its nutrients • As a result, it may not be able to support the further growth of vegetation • The reduction in vegetation due to the cutting down of trees and the use of improper agricultural practices may upset the water cycle • Clearing large amounts of forests may result in a reduction in precipitation by at least 20% and an increase of evaporation by 30% • This reduction in the amount of moisture in the atmosphere and the intensification of the dry condition could prolong a drought o Climatic changes • Global warming that raises the average temperature of the Earth’s atmosphere could aggravate a drought condition especially in hot and dry regions • Higher temperatures cause a higher rate of evaporation, thus depleting the water resources available in the area o Excessive use of wells and irrigation • Wells and irrigation systems in dry areas have improved the lives of people living there • These facilities provide a source of water supply to meet the daily needs of the people as well as the water demands of their agricultural crops • However, during dry periods, the excessive drawing of water for such purposes reduces the availability of water, and may worsen the drought condition
Impacts of droughts • Social impact o Health problems As temperatures soar, the death rate increases especially among the elderly as they are more prone to heat stroke and other health problems related to dry and hot weather o Disintegration of rural communities Many farmers faced with the hardships of drought may have to sell their land and move to the cities An entire rural community may be broken up as a result of this
Loss of lives Water is an essential element for the cultivation of crops and the survival of human beings A prolonged drought affects the growth of crops and hence the supply of food This could lead to widespread famine and loss of lives due to starvation and malnutrition Economic impact o Loss of income As water is vital to crop cultivation, a severe drought could lead to crop failure It could also cause the death of livestock due to starvation and thirst This means a loss of income farmers and higher prices for consumers With little or no income, farmers will have to borrow money to purchase feed for the surviving stock and import water to keep them alive Their inability to repay their debts could lead to the loss of their farmland o Devastation of economy Prolonged drought leads to widespread famine The entire economy of the country affected may collapse, especially if the country is heavily dependent on the earnings from agricultural produce Environmental impacts o Forest fires Due to the hot and dry weather created by droughts, forest fires may become common o Desertification Droughts alone do not cause desertification Improper agricultural practices may worsen the dry condition As a result, the water table drops and vegetation dies Without plants to protect the soil, the topsoil is easily eroded and removed by the wind and the sporadic rainfall This could cause severe dust storms and the extension of desert areas o Reduction in aquatic life As dams, rivers and streams dry up, the water quality will decline This may lead to the growth of toxic algae and result in unsafe drinking water Fish and other aquatic life that used to live in the rivers and streams may not survive the toxic environment o
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Drought LORMS • Cloud seeding o This method introduces particles into the air with airplanes or rockets to encourage condensation to make artificial rain. It is an appealing method, as it does not require the construction permanent and costly structures such as a dam.
This method has been practiced in China where cloud seeding has been used to overcome droughts. o This method is successful, as rain has been brought about by this method. o The method is limited because it is may be very expensive and not effective; rain has not always been brought about using this method. Advanced technology o The use of modern technology to convert seawater to drinking water is another way to overcome water shortage. The process called desalination has been used in Singapore to convert seawater into clean drinking water through the reverse osmosis process. o This method is successful as water would be easily available especially by nations located close to large bodies of saltwater. o The method is limited because of the high cost involved in attaining the technology required. Remote sensing o Advanced technology such as satellite-based remote sensing can be used to monitor water availability and to locate the presence of underground water in different geological sites. Remote sensing can be used for drought surveillance. This may also provide an early warning to minimize the effects of an impending drought. o This has been used in the USA to look for water in Death Valley. o This method is successful because if water is found, it could potentially solve the problem with droughts. o This method is limited because it is highly expensive and less developed countries may not be able to afford for the technology involved. o
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