Dear Xiong,

Merry X-mass. I have a published paper in Journal of
Agricultural Meteorology , 2005, Vol 60 (5): 637-640.

entitled: Effects of global climate change on water
resources. I have discussed a little on the effect of
CO2 fertilization on ET and crop which u can find it
below. If u need full paper I can send it to u.

Evaporation is greatest in the warm waters of the
low-latitude tropical ocean, where solar heat input is
greatest. Global atmospheric circulation patterns tend
to distribute this moisture poleward to higher
latitudes, where it cools and condenses into rain.
This condensation releases large amount of latent heat
(Hardy, 2003). Global warming would tend to increase
evapotranspiration (ET) rates and irrigation water
requirements.  Ideally, a warmer atmosphere can also
hold more water, but the actual change in evaporation
will depend on both the ability of the atmosphere to
hold the water and the changes in wind patterns.
Projections show that a temperature rise of about 2°C
could cause a potential increase in evaporation by 40%
in a humid temperate region (IPCC, 1996). Similarly,
reviews of the state-of-the-art climate models suggest
that with the doubling of atmospheric CO2
concentration, global average evaporation may increase
by 3 to 15 percent (Gleick, 1998).
   Transpiration (water loss into the atmosphere from
plants) is dependent on various factors, including
plant type and plant cover, root depth, stomata
behavior, and the concentration of CO2 in the
atmosphere. Research shows that some groups of plants
will lower water use when exposed to a higher
concentration of CO2. The direct effects of elevated
CO2 (the rate of increase of atmospheric CO2
concentration has been about 1.5 ppm or 0.4% per year
over the past two decades) on plants is likely to
cause increases in stomatal resistance (Bouwer, 2003),
which will also tend to reduce evapotranspiration.  On
the other hand, some studies suggest that plants grow
more in an environment that has a higher level of CO2
gas. As a result, there will be an increase of leaf
area of those plants, which in turn increases water
use. The elevated CO2 will stimulate increases in
plant leaf area (probably for C3 plants) and canopy
temperature (Bouwer, 2003), both of which increase
evapotranspiration. Some plants are found to
acclimatize to increased CO2 levels (Hardy, 2003).
However, the real world is quite different from the
laboratory setting. It is, therefore, difficult and
inappropriate to generalize the results.


Best regards,

M. E. Asadi



Tel: 0098-171-3354868 (office)
Mobile phone: 0098-0911-175-2719
Fax: 0098-171-3359813
Mailing Address:

Mr. Asadi, Mail Box 49175-639, Gorgan, Iran


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around
http://mail.yahoo.com