March
8, 2007 Manmade climate
change due to
pollution seriously inhibits precipitation over hills in semi-arid
regions, a
phenomenon with dire consequences for water resources in the Middle
east and
many other parts of the world, a study by a Chinese-Israeli research
team, led
by Prof. Daniel Rosenfeld of the Hebrew University of Jerusalem, has
shown. The Chinese and
Israeli
researchers showed that the average precipitation on The research study,
published in
the current issue of the journal Science,
is titled "Inverse Relations between Amounts of Air Pollution and
Orographic Precipitation" and was written by Prof. Rosenfeld of the
Hebrew
University's Ring Department of Atmospheric Sciences, Jin Dai and
others from
the Meteorological Institute of Shaanxi Province, China, and Zhanyu Yao
of the
Chinese Academy of Meteorological Science. These findings
highlight the
threat to vital water resources in polluted regions of the world where
hilly-area precipitation makes a significant contribution to the
regional water
supply, as in the southwestern The precipitation
inhibition
process occurs as water vapor condenses on the pollution particles and
creates
a cloud with a large number of drops that are so small that they float
with the
air and are slow to coalesce into raindrops or to freeze into sleet and
snowflakes. This slowing translates into a net loss of precipitation
when the
cloud "lifetime" is shorter than the time necessary to release its
water. This is the case for clouds that form when they ascend across a
ridge
and then descend and evaporate on the downwind side. By making use of
precipitation
and visibility records that show a direct causal link between the
airborne
particle pollution and the mountain precipitation losses, the unique
China
study can serve as a template to bear out hypotheses about the effects
of
pollution on rainfall that were undertaken previously by Prof.
Rosenfeld in
hilly regions with similar pollutive conditions. These include Atmospheric aerosols
have been
described in earlier studies as playing a role in cooling the
atmosphere by
reflecting some of the incoming solar radiation back into space -- thus
serving
as a counterbalance to global warming resulting from the release of
greenhouse
gases. The latest study by Prof. Rosenfeld and his Chinese associates
shows,
however, that this "beneficial" effect is offset by the proven direct
link between air pollution and decreased mountain precipitation, and
that
climate change means much more than "just" global warming.
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