首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Water will evaporate from any wetted surface. A .significantly large fraction of the rainfall that falls on land is returned to
Water will evaporate from any wetted surface. A .significantly large fraction of the rainfall that falls on land is returned to
admin
2011-04-26
75
问题
Water will evaporate from any wetted surface. A .significantly large fraction of the rainfall that falls on land is returned to the atmosphere in this fashion. In addition water is assimilated by root systems of growing plants and is later transpired from the leaf surfaces by a process essentially identical to evaporation. The two effects, evaporation and transpiration, cannot be individually discriminated for their effectiveness in returning rainfall to the atmosphere, but their sum contribution can be evaluated and is usually called the evapotranspiration factor. The fraction of rain falling on the United States that is returned to the atmosphere by evapotranspiration, for example, is 70 percent; for the world as a whole, approximately 62 percent. In arid countries such as Australia the fraction is larger, and in less arid areas such as the United Kingdom it is lower. Water returned to the atmosphere by evapotranspiration is unavailable to man, except in, the sense that useful plants may be grown in the place of useless ones. It cannot be trapped and redistributed for industrial or other purposes.
In regions of low rainfall, plant cover will develop to a point where all precipitation is used in evapotranspiration and none remains for stream now. Seasonal rainfalls provide a qualifier for this statement because streams will flow even in the most arid areas during periods of maximum rainfall. In general, if the potential evapotranspiration—that which would result from the maximum plant cover a region could support under ideal circumstances—should exceed the precipitation, overland stream flow ceases. Conversely, if evapotranspiration is less than precipitation, runoff is generated.
The amount by which precipitation exceeds evapotranspiration is the perennial yield of stream flow water, and this is the usable fraction of rain and snowfall. Across the entire United States the water yield amounts to 30 percent of the total rainfall, or approximately 1.77×1015 liters per year. But when we consider the distribution of water deficiencies and surpluses we find that essentially the entire eastern half of the United States, together with a small region in the Pacific northwest, enjoys water surplus, while most of the country to west of the Mississippi is water- deficient and arid.
According to the passage, the water that is available to us is ______.
选项
A、equal to the precipitation
B、purified by useful plants
C、the fraction of water that is not evaporated
D、the rain falling and the snow melted
答案
C
解析
转载请注明原文地址:https://kaotiyun.com/show/so6O777K
0
考博英语
相关试题推荐
Whenataterminalforpublictransportation,neverleaveyourluggageunattended.
ReadtheinformationbelowaboutmakinginternationalpaymentsthroughtheInternet.Choosethecorrectwordtofilleachgap,f
NOTJUSTASHOP!Inhisyearlyreport,theChairmanofachainofretailoutletswritesaboutthefinancialaspectsofthe
Lookattheadvertisementbelow.Itshowsservicesofferedbyabusinessconsultancy.Forquestions6-10,decidewhich(A-H)wou
Readthearticlebelowaboutasuccessfulbusinesspartnership.Foreachquestion(23-28)ontheoppositepage,choosethecorrect
Surprisinglyenough,modernhistorianshaverarelyinterestedthemselvesinthehistoryoftheAmericanSouthintheperiodbefo
Severaltrialeffortsinthe1980sprovedthatitwasfinancially______torestoreoldbuildings.
Becauseofdifficultiesingettingavisa,thestudentshadto______theideaofapplyingforstudyintheUnitedStates.
Hisjobwassotiringthathefeltabsolutely______.
TheCommitteehasapprovedyourqualificationsandyouwillhe______astheretiringHeadClerk’spost.
随机试题
在低温季节施工时,混凝土出机口温度应每()h测量1次。
简述《独立宣言》的基本内容。
上能清肺润燥,中能清胃生津,下能滋阴降火的药物是
A.肺动脉瓣区第2音(P2)亢进B.剑突下示心脏抬举性搏动C.心浊音界缩小或叩不出D.颈静脉充盈E.双下肺湿哕音
下列施工安全的制度保证体系中,属于日常管理制度的是()。
有人将社会人口分为“高端人口”与“低端人口”。这种带有明显歧视导向的论调,抹杀的是包括农民工在内的普通劳动者的社会贡献,以及他们的尊严。而承认普通劳动者的尊严实际上是承认()。
下列科学常识表述不正确的是()。
人力资源管理费用不包括()。
Therehasbeennothingmoreastonishingintheprogressofwarwhichisreallytheapplicationofthemechanicsofforcetohuma
Mostpeopleareawarethatoutdoorairpollutioncandamagetheirhealth,butmanydonotknowthatindoorairpollutionalsoca
最新回复
(
0
)