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
83
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
Lookattheorganizationchartbelow.Itshowstheresponsibilityofeachmanager.Whoseresponsibilitydoeseachsentence(11-1
Lookatthechartsbelow.Theyshowthesalesofcarsindifferentdepartmentstoresduring2006,2007and2008.Whichchartdoe
Readthememoandtheletterbelow.Completethecustomercomplaintform.Writeawordorphrase(inCAPITALLETTERS)ornumber
Readthearticlebelowfromacompany’sstaffmagazine,aboutarecenttrainingcourse.Foreachquestion(23-28)ontheopposite
Readthenewspaperarticlebelowaboutapartnershipbetweenindustryandschools.Aresentences16-22belowthearticle"Ri
Salesin1990fluctuatedbeforedroppingsharply,whereasin2000salesremainedconstantthroughouttheperiod.
•Lookatthelistbelow.Itshowsthebusiness-to-businessservicesofferedbyaconsultancygroup.•Forquestions6-10,decide
Inaperfectlyfreeandopenmarketeconomy,thetypeofemployer—governmentorprivate—shouldhavelittleornoimpactonthe
Nobodyatworkisveryhappy,becauselastweek’ssalesfigureswerepretty______.
随机试题
绿色方向指示信号灯的箭头方向向左,表示准许车辆左转弯。
属于反治的是()
下列各项,不属亡阳证表现的是()
钢筋和混凝土两种材料能有效结合在一起共同工作,下列何种说法不正确?[2005年第69题]
营造行道树一般以()为主,以路中心线为轴线,在公路两旁营造单行或双行的树木。
对于拆除工程,建设单位应在拆除工程施工前( )日内,将相应资料报送建设工程所在地的县级以上地方人民政府建设行政主管部门或者其他有关部门备案。
衡量财政支出规模的指标包括()。
越来越多的有说服力的统计数据表明,具有某种性格特征的人易患高血压,而另一种性格特征的人易患心脏病,如此等等。因此,随着对性格特征的进一步分类研究,通过主动修正行为和调整性格特征以达到防治疾病的可能性将大大提高。以下哪项最能反驳上述观点?
请在【答题】菜单中单击【考生文件夹】按钮,并按照题目要求完成下面的操作。注意:以下的文件必须保存在考生文件夹下。打开考生文件夹下的演示文稿yswg.pptx,根据考生文件夹下的文件“PPT-素材.docx”,按照下列要求完善此文稿并保存
InBritain,winteristheseasonnotonlyforvisitstothetheatre,opera,concertsandballet,butalsoforshoppingorforsi
最新回复
(
0
)