九年级英语上册 Module 11 Population Growth,Water Shortages文章背景材料 外研版

PopulationGrowth, Water Shortages

Theworld's population, at nearly 6 billion, is growing by about 80million people

eachyear. This number implies an increased demand for freshwater of about billion

cubicmeters a year—an amount equivalent to the entire annual flow rateof the Rhine

River.While population growth rates have slowed somewhat, the absolutenumber of

peopleadded to the population each year—the relevant figure whenconsidering the

availabilityof and need for freshwater—remains near historic highs. Forexample,

becausenearly 2 billion people have been added to the planet since 1970, percapita

availabilityof water is one-third lower now than it was then. China

andIndia, the world's first and second most populous countries, provideexamples

ofhow even modest population growth rates translate into large absolutenumbers

whenthe population base is large. In China the population growth rate isabout 1%

peryear, estimated in 1998. Nevertheless, because China's population isover 1.2

billionpeople, even a low population growth rate means 12 million additionalpeople

eachyear. India's population growth rate, which is substantially higherthan

China's,at about 1.9% per year, means about 18 million people added each yearto

India'scurrent population of about 970 million. In thetwo

regionsof the world that already face the most serious absolute or seasonal

shortagesof water—Africa and the Near East—population growth rates remainamong

thehighest in the world. In sub-Saharan Africa population is growing byan average

2.6%a year; in the Near East and North Africa, by 2.2%. These populationgrowth

rateshave ominous implications for per capita water supply in thecountries of these

regions.Waterstress and scarcity.As their populations grow, more and more

countriesare facing water shortages. A country is said to experience waterstress

whenannual water supplies drop below 1,700 cubic meters per person. Atlevels

between1,700 and 1,000 cubic meters per person, periodic or limited watershortages

canbe expected. When annual water supplies drop below 1,000 cubic metersper person,

thecountry faces water scarcity. Once a country experiences waterscarcity,it can

expectchronic shortages of freshwater that threaten food production, hinder

economicdevelopment, and damage ecosystems. Malin

Falkenmarkdeveloped the concepts of water stress and water scarcity based on an

indexof per capita freshwater needs. She estimated a minimum need of 100liters

perday per person for household use and from 5 to 20 times as much foragricultural

andindustrial uses. These concepts have been widely accepted and used by

hydrologists,the World Bank, and other organizations. For example, Population

ActionInternational (PAI) has relied on them to make projections of percapita water

availabilityand to forecast water shortages in 2025 and 2050.

Calculationsof water stress and water scarcity are based on estimates of acountry's

renewablefreshwater supplies and do not include water withdrawn from fossil

groundwater.Fossil groundwater is essentially a nonrenewable resource: It takes

tensof thousands of years for these deep aquifers to replenishthemselves. A country

maytemporarily avoid the effects of water stress by mining itsnonrenewable water

supplies,but this practice is not sustainable, particularly if the population

continuesto grow rapidly and per capita demand for freshwater increases.

Asof 1995, 31 countries, with a combined population of over 458million, faced either

waterstress or water scarcity. This represents an addition of only 3countries since

1990,when 28 countries, with a combined population of 335 million facedchronic

waterstress or water scarcity. The number of people estimated to live in

water-scarceand water-stressed countries rose by nearly 125 million during these

fiveyears, however, largely reflecting population growth in water-shortcountries.