蒸散是水循环和能量平衡的重要载体.其重要性不言而喻.作为陆地和大气交互的重要物质和能量流的
传输体,蒸散的剖切需要得到理解.
1.蒸散理解的历史痕迹
纵观中西方的文化和历史发展,从蒸散中也能细微的品味到差异.
中国,讲水循环就引用屈原的天问,柳宗元的天对.我们对自然的认知过程都散落在文豪的诗句中.
多是概念的理解,而没有任何逻辑推导过程可以遵从.
而西方的发展,则完全不同了.密切的和物理的发展联系在一起.从理解物质的组成,粒子的可分性等方面
具有明晰的逻辑思维过程.brutasert在蒸散的书中给了详尽的论述.
1802年DELTON提出的蒸散计算方法是重要的里程碑.
2.DELTON,能量平衡,penman
三种方法都是很经典的估算蒸散的方法.
DELTON,能量平衡都需要知道地表的温度,而这几乎是不可能的.
penman结合了两者,消除了对地表温度的依赖.
然后对于潜在蒸发的争论就没有停歇过.
而对于蒸发皿观测资料过去50年的降低,却很难得到有效的气候变化的信息.
大部分的解释都来自于基于penman公式的解释.
3.互补相关模型
如果尺度足够大,那么受到平流等的局部作用就很小.能量输入和输出可以认为守恒.
所以互补相关在大尺度上理解能量和水量平衡是没有问题的.
但是这个尺度多大?不知道.
在小的蒸发皿而言,输入Rn明显和蒸发观测不相等.
从蒸发皿-湖泊-大海,其对大气的反馈作用是不同的.
所以在小尺度内讲互补是不可行的.
此外时间尺度的差异也融合在里面.
不同时间尺度,里面揉合的东西也不同.
4.遥感蒸散
遥感蒸散正好处在了尴尬的境地.
像元尺度,瞬间.
如何利用遥感的信息,如何来消除短板.

最后,morton 1990年的部分转载如下:
The third lesson is thal we know surprisingly
little about hydrology. In fact we
know so little that we think we know a lot.
Until such time as this illusion is abandoned,
the financial resources and
scientif ic skills will continue to be directed
away f rom the kind of original research that
is needed to jolt hydrology out of its long
period of stagnation.

The fourth lesson is that a similar situation
exists in many of the related
environmental sciences. For example,
ldso (1984a, 1984b) and ldso and Brazel
(1984) have criticized the predictions of
the Carbon Dioxide Assessment Committee
of the U.S. National Research Council
(1983) that a doubling of the atmospheric
carbon dioxide content would cause a near
surface temperature rise of approximately
3 degrees Celsius and would be associated
with a 40 to 75 percent reduction in
the streamflows for the major watersheds
in the western United States. The grounds
for these criticisms are (1) that the prediction
is contrary to the available evidence;
(2) that the models used to produce the
predictions ignore the existence of a number
of confutative feedback mechanisms,
one of which concerns the way that increased
carbon dioxide concentrations
decrease transpiration by causing the stomala
to contract. Moreover, after
discussing feedback mechanisms that
could affect the relationshio between over-
grazing and desertif ication, ldso (1 981)
concluded by stating: "Consequently,
more basic research into boundary layer
processes appears necessary to provide
the additional and improved algorithms required
to make the (general circulation)
models more descriotive of the real world".


The fifth lesson is that there is a real
need for an alternative approach to environmental
research. Such an approach
should involve a study of natural systems
as they actually exist after feedback mechanisms
have modified, or even reversed,
the effects of small-scale orocesses. lt is
exemplified in the Gaia hypothesis (Lovelock,
1979, 1986), the accomplishments of
the Bergen School of Meteorology (see
Jewell, 1981)and the development of the
complementary relationship models (Morton,
1983a, 1986a) for estimating actual
areal evapotranspiration and lake evaporation.
Although not used nearly as often
as the linear cause-and-effect approach,
this alternative has a much better record of
success.


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