Environmental Engineering Reference
In-Depth Information
and the Caribbean 6.2 percent; and north east and north Africa 4.6 percent
(ICRISAT 2008 ). Deserti
cation and droughts have their greatest impact in Africa
where two-thirds of the continent is desert or is water scarce.
In economic theory, drinking water is partly a public good and partly a normal
consumption good. In North America, a large portion of drinking water is used
outside the home as a normal good for uses such as gardening and washing cars.
Domestic water use in the US averages between 80 and 100 US gallons (302
378
L), whereas in Canada the per capita consumption is 343 L, but only about
10 percent of it is for drinking and cooking. However, with very few exceptions, all
publicly supplied water is treated to drinking water standard, partly for fear that
untreated water could lead to illness.
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1.2.1 Climate Change and Water
Dore ( 2005 ) surveyed the evidence for changing global patterns of precipitation. This
subsection is based on those
findings. It appears that annual land precipitation has
continued to increase in the middle and high latitudes of the Northern Hemisphere
(very likely to be 0.5
1 percent per decade), except over Eastern Asia. Over the
subtropics (10 ° N - 30 ° N), land-surface rainfall has decreased on average (likely to be
about 0.3 percent per decade), although this has shown signs of some recovery. But
this recovery could simply be evidence of increased variability. Tropical land-surface
precipitation measurements indicate that precipitation has probably increased by
about 0.2
-
0.3 percent per decade over the twentieth century, but increases are not
evident over the past few decades and the amount of tropical land (versus ocean) area
for the latitudes 10
-
S is relatively small. Nonetheless, direct measurements of
precipitation and model reanalyses of inferred precipitation indicate that rainfall has
also increased over large parts of the tropical oceans. Where and when available,
changes in annual stream-
°
N
10
°
-
ow often relate well to changes in total precipitation. The
increases in precipitation over the Northern Hemisphere mid- and high-latitude land
areas have a strong correlation to long-term increases in total cloud amount. In contrast
to the Northern Hemisphere, no comparable systematic changes in precipitation have
been detected in broad latitudinal averages over the Southern Hemisphere.
Decreasing snow-cover and land-ice extent are positively correlated with
increasing land-surface temperatures. Satellite data show that there is very likely to
have been decreases of about 10 percent in the extent of snow cover since the late
1960s. There is a highly signi
cant correlation between increases in Northern
Hemisphere land temperatures and decreases in snow cover. There is ample evi-
dence to support a major retreat of alpine and continental glaciers in response to
twentieth-century global warming. This evidence has continued to grow over the
period 2010
2014. In a few maritime regions, increases in precipitation due to
regional atmospheric circulation changes have overshadowed increases in temper-
ature in the past two decades, but overall glaciers in the northern and southern
hemispheres have continued to shrink.
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