Encyclopedia of Global Resources part 35 ppsx

Three main types of diatomite deposits are recognized in the United States: marine rocks near continental margins, lacustrine rocks formed in ancient lakes or marshes, and sedimentary ro

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other elements, although exact proportions vary

Pu-rified diatomite is essentially silica (SiO2), with an

av-erage molecular mass of 60.8 Diatomite has a melting

point of 1,710° Celsius and a density of 2.3 grams per

cubic centimeter Heating it to high temperatures

forms crystalline silica

Diatomite is usually white (if pure), buff, gray,

and rarely black In situ, it is generally found as a soft

sedimentary rock or as powder Raw diatomite is

typi-cally processed by a series of crushing, drying,

size-reduction, and calcining procedures to produce

dif-ferent grades of diatomite for difdif-ferent specialized

applications

Description, Distribution, and Forms

Diatomite is a soft, chalklike, fine-grained

sedimen-tary rock composed primarily of the fossilized silica

shells of microscopic algae called diatoms It is finely

porous, is low in density, and has low thermal

conduc-tivity Diatom frustules are composed of two

symmetri-cal silica valves, which can be elaborately ornamented

with tiny holes and protrusions These tiny holes are

what make diatoms an ideal material for filtration

The word “diatom” comes from Greek diatomos,

meaning “cut in half,” because of the two valves

Diatoms live in a wide range of moist

environ-ments, although most abundantly in marine (oceanic)

and lacustrine (freshwater) environments Three main

types of diatomite deposits are recognized in the

United States: marine rocks near continental margins,

lacustrine rocks formed in ancient lakes or marshes,

and sedimentary rocks in modern lakes, marshes, and

bogs Another commonly used term for diatomite,

diatomaceous earth, more properly refers to

uncon-solidated or less lithified forms of diatomite

One of the most important marine diatomite

de-posits is near Lompoc, California, reported to be the

world’s largest producing district by volume

Eco-nomically important lacustrine deposits in the United

States are found in Nevada, Oregon, Washington, and

eastern California In 2007, the United States

pro-duced 33 percent of the world’s diatomite Other

lead-ing producers were China (20 percent), Denmark (11

percent; all moler diatomite, containing 30 weight

per-cent clay), Japan (6 perper-cent), and France (4 perper-cent)

History

Some of the earliest references to diatomite are to the

ancient Greeks’ probable use of it to form lightweight

bricks for building; they also used diatomite as an

abrasive In 535 c.e., the Roman Emperor Justinian I used diatomite bricks in building the church of St So-fia in Constantinople (now Istanbul)

Diatomite use became industrially important to Western Europe after 1867, when Alfred Nobel in-vented dynamite Pulverized diatomite was com-monly used to absorb and stabilize the nitroglycerine used to make dynamite By the late 1800’s, the United States had become the primary producer of diato-mite By 1900, diatomite’s uses had expanded to in-clude many of its present-day uses, including beer filtration and building materials

During the 1920’s, techniques for calcining (ther-mally treating) and grading diatomite enabled a wider variety of uses for this resource By World War II, the U.S Army and Navy made wide use of diatomite to purify drinking water, to remove oil from boiler and engine water, and to create low-light-reflectance paints for ships

Obtaining Diatomite Because of its abundance and usual occurrence near the surface in the United States, most diatomite pro-duced is obtained from open-pit mines The diato-mite is excavated by machine after the overburden is removed Outside the United States—particularly in China, Chile, and France—underground diatomite mining is fairly common These mines are usually pit-and-pillar mines excavated by machine, although some small mines are excavated using hand tools In Iceland, diatomaceous mud is dredged from Lake Myvatn Diatomite is often dried in the open air near the mine before processing

Diatomite processing is often carried out near the mine from which it is extracted Raw diatomite may contain up to 65 percent water and is expensive to transport Primary crushing of ore is usually done with spiked rolls and hammer mills, reducing the ore

to 1.25-centimeter pieces while limiting damage to the diatom structure

Passage through heated air, milling fans, and air cy-clones further dries the diatomite and begins to clas-sify for size as well as remove impurities of different density Processing aims to separate individual diatom valves without destroying their structure, which is key

to filtration uses

Calcining, which increases filtration rate, specific gravity, and particle hardness, as well as oxidizing iron, is usually done with rotary kilns Calcining is par-ticularly important for filter grades

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Uses of Diatomite

Diatomite is primarily used as a filtration medium but

also is used for insulation, as a filler and absorbent,

and as a mild abrasive, in addition to some specialized

medical uses The most common use of diatomite is in

filtration, because of its finely porous nature These

uses include water purification, beer and wine filter-ing, and the removal of oils from water As a water fil-tration element, diatomaceous earth usually is used as

a layer on a filter element or septum (a permeable cover over interior collection channels), called pre-coat filtration Diatomite water filtration systems are

Data from the U.S Geological Survey, U.S Government Printing Office, 2009.

51,000 27,000 24,000

110,000

60,000 33,000 32,000

653,000 130,000

Metric Tons

700,000 600,000

500,000 400,000

300,000 200,000

100,000 United States

Mexico

Japan

Italy Iceland

Germany

Peru Spain

Other countries

25,000

440,000

76,000 24,000 52,000

220,000

71,000

Czech Republic

Costa Rica

Commonwealth of

Independent States

China

Chile

Denmark

(processed)

France

Diatomite: World Mine Production, 2008

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lightweight, cheap, and simple and can remove

bacte-ria and protozoans as well as cysts, algae, and asbestos

This usage of diatomite first became important

dur-ing World War II, when the U.S Army needed a water

filter suitable for mobile military operations The first

municipal diatomaceous-earth water filtration system

was set up in 1948, and more than two hundred

oper-ate presently in the United Stoper-ates Diatomite is also

used to filter nonpotable water, such as that which is

used in swimming pools

Diatomite began to be used after Prohibition to

fil-ter beer and wine in the United States, replacing

wood pulp in filters It is also used to filter liquid

sweet-eners, oils and fats, petroleum and other chemicals,

and pharmaceuticals

Another major use of diatomite is in building,

where it is used for lightweight blocks and bricks and

for thermal insulation (high clay-content Danish

moler in particular) Diatomite is also a frequent

ce-ment additive; diatomite for cece-ment requires less

pro-cessing

As a filler, diatomite has many uses In addition to

providing bulk, diatomite can reduce reflectivity in

paints, reduce caking in granular mixtures, and

pro-vide a variety of effects in plastics, including

prevent-ing film stickprevent-ing Diatomite is absorbent and often

used for cleaning industrial spills and in cat litter

As an insecticide, diatomite is less toxic than

chem-ical pesticides, as it works by absorbing lipids from

in-sects’ exoskeletons, causing dehydration However, it

harms beneficial insects as well as pests Diatomite

also is used as a growing medium for hydroponics and

an additive in various types of potting soil, because

it retains water and nutrients while draining quickly,

similar to vermiculite Medical-grade diatomite is

some-times used for deworming, as the sharp edges of the

frustules are thought to kill parasites, but the efficacy

of this is questionable

Diatomite is also used in cosmetics—for example,

in facial masks to absorb oil—and as a minor abrasive

in jewelry polishes and toothpastes Some processes

for extracting and purifying DNA use diatomite, which

will remove DNA but not RNA or proteins Diatomite

and a highly concentrated denaturing agent are used

to remove DNA, and then a slightly alkaline, low ionic

strength buffer (such as water) can be used to extract

DNA from the diatomite

While diatomite can be replaced by other

materi-als—such as silica sand, perlite, talc, ground lime,

ground mica, and clay—for most of its applications,

its abundance, availability, and low cost make it a pop-ular and heavily used resource

Melissa A Barton

See also: Clays; Lime; Silicates; Water

Commodity Summaries, 2009

Data from the U.S Geological Survey,

U.S Government Printing Office, 2009.

Filter aids 52%

Cement additives 26%

Absorbents 12%

Fillers 9%

Biomedical 1%

U.S End Uses of Diatomite

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Dimension stone

Category: Mineral and other nonliving resources

Where Found

Dimension stone, or natural stone, is mined in

quar-ries around the world The largest concentrations

are found in China, India, Italy, Canada, and Spain In

the United States, a country that produces less than

15 percent of the worldwide supply (although it is the

dominant market for the stone), quarries are found

in thirty-five states, principally (in order of

percent-age) Indiana, Vermont, Georgia, Wisconsin, and

Mas-sachusetts

Primary Uses

Dimension stone is used primarily for domestic

deco-rating and home improvements in upscale housing It

also provides massive block foundation support for

large-scale engineering projects, as well as material

for monuments, memorial stones, and walkways

Technical Definition

Dimension stone is any natural rock—igneous,

meta-morphic, or sedimentar y—precisely cut from a

quarry to a specific size (in blocks or slabs) for a

spe-cific function (as opposed to crushed stone, which is

fractured rubble blasted from quarries to facilitate its

removal) Commercially, granite is the most widely

used (about one-third of the dimension stone

quar-ried), followed by limestone, marble, sandstone, and,

to a much lesser extent, slate and travertine The

deci-sion about which class of dimendeci-sion stone is to be

used is based on color and texture as well as

appear-ance and durability

Description, Distribution, and Forms

Because dimension stone requires precise mining,

must maintain a usable appearance throughout the

excavation process, and has a comparatively high

ex-pense in transportation, it accounts for roughly only 2

percent of the total rock mined annually In the

United States, for instance, approximately 1.4 million

metric tons of dimension stone are mined annually

Dimension stone can be either rough block (for heavy

construction and residential foundations) or dressed

block (for statuary, paving stones, and domestic

deco-ration), with its distinctive luster In fact, finish also

is used to classify types of dimension stone In

addi-tion to being reflective, surfaces can be pitted, nonreflective (both smooth and rough), and pat-terned (often produced by hand)

The four principal types of dimension stone— granite, limestone, marble, and sandstone—are graded by color, grain, texture, mineral patterns and swirls, natural surface finish, durability, strength, and mineral makeup For instance, dimension granite, an igneous rock, is valued for its relative availability; its durability in the face of weathering and environmen-tal pollution, specifically acid rain, because it is most often used for exterior construction projects; its uni-form texture; its hardness; and its variety of colors Di-mension limestone, a sedimentary rock composed largely of calcite, is easy to cut into massive blocks and, although not impervious to acid rain, is remarkably durable (the Pyramids at Giza are made of dimension limestone) However, because of dimension lime-stone’s enormous weight, it is used primarily for foun-dations and smaller buildings Dimension marble is a metamorphic rock that is both durable and strong With its exquisitely smooth, polished surface, marble can be cut into large blocks (up to 63 metric tons) and used to create spectacular public buildings (for in-stance, the Taj Mahal and the Lincoln Memorial) Di-mension sandstone, a sedimentary rock, is most often light gray or yellowish-brown; however, its tendency to streak because of weathering creates striking, aesthet-ically appealing striation effects Its surface is coarse and finely grained It is particularly fragile, suscepti-ble to weathering, and has to be replaced; thus it is limited in its uses

History Using carefully cut, ponderous blocks of durable rock for major engineering undertakings dates to antiquity

in both the Far East, predominantly China, and the Mediterranean basin, most notably the stunning pyra-mid constructions in Egypt, the marble temples around Athens, and the mosques of Turkey By the Re-naissance, rich mineral deposits of marble and gran-ite in Italy and Spain were being utilized to construct great cathedrals and a wide variety of public build-ings, courthouses, and palaces Because of the precise method for cutting the stone, as well as the often ex-traordinary cost of transporting a massive amount of chiseled rock without damaging its integrity, dimen-sion stone was used almost exclusively for public proj-ects financed by monarchies, the Catholic Church, or wealthy aristocrats

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Large deposits of granite, limestone, and marble

found in New England and in the Middle Atlantic

states, most notably Tennessee and Indiana, made

di-mension stone affordable in the New World

Dimen-sion stone played an enormous role in shaping the

look of (and providing the architectural support for)

many public edifices and private residences across the

United States By the mid-twentieth century, however,

newer building materials—reinforced concrete,

alu-minum, and steel—eclipsed dimension stone That

changed dramatically when environmental concerns

about the pollution created by the production of

those construction materials returned attention to

all-natural dimension stone In addition, the home

building boom in the United States during the 1990’s

created a market of upscale consumers interested in

using natural stone to decorate their custom-built

homes In the same decade, interest in dimension

stone was bolstered by large-scale public construction

projects, most notably the Denver International

Air-port, the Korean War Veterans Memorial, the

Na-tional World War II Memorial, and the Franklin

Del-ano Roosevelt Memorial (the latter three are located

in Washington, D.C.)

Obtaining Dimension Stone

The process of obtaining dimension stone—drilling,

extracting, cutting, shaping, and polishing—is

usu-ally tailored to follow a specific mining order;

dimen-sion stone is seldom mined without a contract for a

particular project Since the 1960’s, extracting

dimen-sion stone has been enhanced, and made

compara-tively easy, by significant developments in

engineer-ing tools Unlike the excavation of crushed stone,

which relies on indiscriminate detonations and heavy

machinery, the recovery of usable dimension stone

requires care Each type of dimension stone requires

its own methodology depending on the needs of the

construction project, the depth of the mineral

de-posit, and the mining operation’s financial resources

The methodology is further impacted by the location

of the vein—whether cutting into a hill (called a

bench quarry) or digging into the flat ground,

opera-tions that can go to 90 meters

Obtaining dimension stone begins with limited

blasting Then jet piercers, which use a high-velocity

jet flame—a concentrated, highly combustible blast

of oxygen and fuel oil shot through a nozzle under

enormous pressure—channel into the quarry face In

the case of marble, limestone, and sandstone, safer

electrical drilling machines with steel chisels that chop channels into the walls and cut away the desired blocks are frequently used; this method is more time-consuming In the case of granite and marble, once channels are created, large blocks are pried from the quarry face or extracted from the quarry mine and cut on site into usable shapes (ranging from 0.3 to

18 meters long and 4 meters thick), called mill blocks Each block is then removed from the quarry area with derricks In turn, these blocks are processed for their specific project, that is, given the appropriate shape, size, dimension, and finish by certified masons who use a variety of precision saws Diamond saws are used most often because of their hardness and their ability

to cut intricately and carefully

Uses of Dimension Stone Despite the availability of less expensive substitute building materials, the extraordinary expense of such precisely cut stone, and the care needed during its transportation, dimension stone has maintained its position within the engineering and architectural fields for close to three millennia Slabs of cut stone, most often granite or sandstone, provide a reliable,

Commodity Summaries, 2009

Data from the U.S Geological Survey,

U.S Government Printing Office, 2009.

Limestone 35%

Granite 32%

Miscellaneous 17%

Sandstone 12%

Marble & slate 4%

U.S End Use of Dimension Stone

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durable, and attractive foundation for both buildings

and residences However, the use of the stone for

spec-tacular building projects is the use most often

recog-nized by people Dimension stone such as granite and

marble is most associated with grand public spaces

and with important monuments dedicated to

histori-cally significant people and events, public buildings

(like banks and government facilities), cathedrals,

grand private homes, upscale hotels, cemetery

head-stone markers, and elegant mausoleums In addition,

thinner cuts of dimension marble are used for

clad-ding, the outer skin of stone applied to buildings to

protect the foundation stone and to give the building

an aesthetic quality

Dimension stone creates an elegant, tasteful, and

earthy feel to home interiors It provides tops for

kitchen counters and bathroom vanities as well as

ma-terial used for staircases and ornamental arches in

homes where owners are interested in creating

dis-tinctive—and expensive—custom-designed interior

effects Because no two slabs of dimension stone are

exactly alike, interior effects can be both striking and

individual Because of the wide variety of textures and

colors in natural stone, homeowners can complete

virtually whatever decorating motif they conceive by

using cut stones for floor tiles, walkways, flagstones,

ornamental statuary, and roofing shingles

Joseph Dewey

Further Reading

Adams, Heather, and Earl G Adams Stone: Designing

Kitchens, Baths, and Interiors with Natural Stone New

York: Stewart, Tabori & Chang, 2003

Bell, Ron Early History of Indiana Limestone

Bloom-ington, Ind.: AuthorHouse, 2008

Dupré, Judith Monuments: America’s History in Art and

Memory New York: Random House, 2007.

Greenhalgh, Michael Marble Past, Monumental

Pres-ent: Building with Antiquities in the Mediaeval

Mediter-ranean Boston: Brill, 2008.

Isler, Martin Sticks, Stones, and Shadows: Building the

Pyramids Norman: University of Oklahoma, 2001.

Web Site

U.S Geological Survey

Minerals Information: Dimension Stone Statistics

and Information

http://minerals.usgs.gov/minerals/pubs/

commodity/stone_dimension/

See also: Diamond; Granite; Igneous processes, rocks, and mineral deposits; Limestone; Marble; Open-pit mining; Sand and gravel; Sandstone; Sedimentary processes, rocks, and mineral deposits

Dow, Herbert H.

Category: People Born: February 26, 1866; Belleville, Ontario, Canada

Died: October 15, 1930; Rochester, Minnesota

Herbert H Dow’s main discovery was that under-ground liquid brine from prehistoric saltwater oceans contained many chemicals He sought a way to extract these chemicals from the Earth and was initially suc-cessful in extracting bromine He later discovered ways

to extract other chemicals from the brine, including magnesium, sodium, calcium, and chlorine His later research led to more efficient methods of extraction.

Biographical Background Although born in Canada, Herbert H Dow lived in that country for about only six weeks His American parents returned to Derby, Connecticut, where his ther worked as a mechanical engineer In 1878, his fa-ther’s company, the Derby Shovel Manufacturing Company, moved to Cleveland, Ohio, and the family moved too In 1884, Dow entered the Case School of Applied Science in Cleveland (now Case Western Re-serve University), where he studied chemistry While still a student at Case, Dow realized the importance of subterranean brine as a source of chemicals His first successful extraction process was for bromine, a chemical used in sleep medicines and by photogra-phers Upon graduation from Case, Dow became a professor of chemistry at Huron Street Hospital Col-lege in Cleveland and continued to work on his re-search to develop a cost-effective method of extract-ing bromine

In 1890, with the assistance of several associates, Dow established the Midland Chemical Company

in Midland, Michigan Midland was selected for the company’s location because of the high-quality bro-mine in the subterranean waters underneath that city

A short time later, because of differences of opinion between Dow and his backers, Dow left Midland and returned to Cleveland, where he founded the Dow

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Process Company After developing methods to

ex-tract chemicals such as chlorine and sodium, Dow

be-came wealthy He moved his company to Midland,

where it became Dow Chemical Company in 1896 By

1900, he had taken over the Midland Chemical

Com-pany

Impact on Resource Use

By 1891, Dow had perfected the electrolysis process of

extracting bromine that became known as the “Dow

process.” Many of Dow’s patents were for efficient

means of extracting chemicals from other substances

Thus, he was able to lower the cost of chemical

prod-ucts and produce those chemicals more efficiently

and effectively For example, in the early 1900’s,

Ger-many was the center of the chemical industry, but

Dow was selling bromine for less than 75 percent of

the price charged in Europe Dow expanded during

World War I by producing chemicals used in

explo-sives Following the war, the company became active

in supplying chemicals to the automobile industry

Dow also improved the quality of gasoline By the time

of his death at the Mayo Clinic in 1930, Dow had

re-ceived more than ninety patents for processes for

ex-tracting chemicals

Although Dow’s research dealt with how to mine

chemicals from ancient oceans, his ideas and

technol-ogy have had broader uses The same methods can be

used to mine modern seas Thus, shortly after Dow’s

death, his company opened its first seawater

process-ing plant Dow was one of the founders of the modern

chemical industry He took halogen science from

the-ory to reality

Dale L Flesher

See also: Bromine; Calcium compounds; Chlorites;

Magnesium; Marine mining

Drought

Category: Environment, conservation, and

resource management

Drought is a shortage of precipitation that results in a

water deficit for some activity Droughts occur in both

arid and humid regions Traditional and modern

so-cieties have evolved methods of adjusting to the drought

hazard.

Background

In order to analyze and assess the impacts of drought,

as well as delimit drought areas, the characteristics of

“drought” must be defined Conditions considered a drought by a farmer whose crops have withered dur-ing the summer may not be seen as a drought by a city planner There are many types of drought: agricul-tural, hydrological, economic, and meteorological The Palmer Drought Severity Index is the best known

of a number of indexes that attempt to standardize the measurement of drought magnitude Neverthe-less, there remains much confusion and uncertainty

on what defines a drought

Roger Graham Barry and Richard J Chorley, in At-mosphere, Weather, and Climate (1992), noted that

drought conditions tend to be associated with one or more of four factors: increases in extent and persis-tence of subtropical high-pressure cells; changes in the summer monsoonal circulation patterns that can cause a postponement or failure of the incursion of wet maritime tropical air onto the land; lower ocean surface temperatures resulting from changes in ocean currents or increased upwelling of cold waters; and displacement of midlatitude storm tracks by drier air

Effects of Drought Drought can have wide-ranging impacts on the envi-ronment, communities, and farmers Most plants and animals in arid regions have adapted to dealing with drought, either behaviorally or through specialized physical adaptations Humans, however, are often un-prepared or overwhelmed by the consequences of drought Farmers experience decreased incomes from crop failure Low rainfall frequently increases a crop’s susceptibility to disease and pests Drought can partic-ularly hurt small rural communities, especially local business people who are dependent on purchases from farmers and ranchers

Drought is a natural element of climate, and no re-gion is immune to the drought hazard Farmers in more humid areas grow crops that are less drought re-sistant In developing countries the effects of drought can include malnutrition and famine A prolonged drought struck the Sahel zone of Africa from 1968 through 1974 Nearly 5 million cattle died during the drought, and more than 100,000 people died from malnutrition-related diseases during just one year of the drought

Subsistence and traditional societies can be very re-silient in the face of drought American Indians either

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stored food for poor years or migrated to wetter areas.

The !Kung Bushmen of southern Africa learned to

change their diet, find alternate water sources, and

generally adapt to the fluctuation of seasons and

cli-mate in the Kalahari Desert

More than any other event, the Dust Bowl years of

the 1930’s influenced Americans’ perceptions and

knowledge of drought Stories of dust storms that

turned day into night, fences covered by drifting soil,

and the migration of destitute farmers from the Great

Plains to California captured public and government

attention The enormous topsoil loss to wind erosion,

continuous crop failures, and widespread

bankrupt-cies suggested that the United States had in some way

failed to adapt to the drought hazard

Federal Drought Response in the

United States

Beginning in the 1930’s, the federal government took

an increasing role in drought management and relief

In 1933, the federal government created the Soil

Ero-sion Service, known today as the Natural Resources

Conservation Service No other single federal

program or organization has had a greater

im-pact on farmers’ abilities to manage the drought

hazard President Franklin D Roosevelt’s

Prai-rie States Forestry Project (1934-1942) planted

more than 93,078 hectares of shelterbelts in the

plains states for wind erosion control The

fed-eral government purchased approximately

400,000 hectares of marginal farmland for

re-planting into grass Federal agencies constructed

water resource and irrigation projects

Post-Dust Bowl droughts still caused

hard-ships, but the brunt of the environmental,

eco-nomic, and social consequences of drought were

considerably lessened Fewer dust storms

rav-aged the plains New crop varieties and better

farming practices decreased crop losses during

drought years Government programs and better

knowledge have enabled families and

commu-nities to better cope with drought

Coping with Future Droughts

Numerous attempts have been made to predict

droughts, especially in terms of cycles However,

attempts to predict droughts one or more years

into the future have generally been

unsuccess-ful The shorter the prediction interval, the

more accurate the prediction Nevertheless,

progress has been made in estimating drought occur-rence and timing For example, the El Niño/South-ern Oscillation may be a precursor to drought in some areas Possibly with time the physical mechanics of cli-mate and drought will be understood adequately for long-term predictions to have value

Perhaps of greater value is the current capacity to detect and monitor drought in its early stages (usually meaning within one to twelve months) Early recogni-tion of potential drought condirecogni-tions can give policy makers and resource managers the extra time needed

to adjust their management strategies Information

on soil moisture conditions aids farmers with planting and crop selection, seeding, fertilization, irrigation rates, and harvest decisions Communities that have a few months’ warning of impending drought can in-crease water storage, implement water conservation measures, and obtain outside sources of water The progress made in the world’s developed coun-tries has not always been available to the developing nations Overpopulation and overuse of agricultural lands have resulted in regional problems of

A drought results from a lack of precipitation that causes massive water short-ages, affecting entire populations of people (©Galyna Andrushko/

Dreamstime.com)

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cation and have impeded the ability of developing

na-tions to respond Monitoring equipment can be

costly Furthermore, drought adjustments used in the

United States may not be applicable to other

coun-tries’ drought situations

David M Diggs

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