Introduction to Drinking Water Management - Global Drinking Water Management and Conservation - page 6

150 years, ground-based observations show that there is very
likely to have been a reduction of about 2 weeks in the annual duration of lake and
river ice in the mid- to high latitudes of the Northern Hemisphere. New analyses
show that in regions where total precipitation has increased, it is very likely that
there have been even more pronounced increases in heavy and extreme precipita-
tion events. The converse is also true. In some regions, however, heavy and extreme
events (i.e. de

Over the past 100

-

ned to be within the upper or lower 10 percentiles) have increased
despite the fact that total precipitation has decreased or remained constant. Where
this has occurred, it is attributed to a decrease in the frequency of precipitation
events. Overall, it is likely that for many mid- and high-latitude areas, primarily in
the Northern Hemisphere, statistically signi

cant increases have occurred in the
proportion of total annual precipitation derived from heavy and extreme precipi-
tation events; it is likely that there has been a 2

4 percent increase in the frequency
of heavy precipitation events over the latter half of the twentieth century. For the
Southern Hemisphere, there is some concern that while extreme precipitation events
have increased, total annual precipitation may have declined (Dore and Singh 2013 ;
Dore and Simcisko 2013 ).
Over the twentieth century (1900

-

1995), there were relatively small increases in
global land areas experiencing severe drought or severe wet conditions. In some
regions, such as parts of Asia and Africa, the frequency and intensity of drought
have been observed to increase in recent decades. In many regions, these changes
are dominated by inter-decadal and multi-decadal climate variability, such as the
shift in the El Ni

-

o Southern Oscillation (ENSO) toward more warm events. But
there is great uncertainty over the change in the frequency and variability of El Ni

ñ

ñ o

and La Ni uence on the distribution of

precipitation. Ocean currents continue to be major in

ñ a events, which typically have a global in

uences on precipitation
everywhere on the globe and so possible changes in any of the major ocean currents
could change precipitation drastically.
Other statistical analyses of rainfall patterns in some of the dryland regions reveal
a steep drop in the early 1970s, which has persisted, a reduction of about 20 percent
in precipitation levels resulting in a 40 percent reduction in surface runoff (EU,
Council of the European Union 2007 ). Furthermore, the International Water Man-
agement Institute predicts that climate change will have dire consequences for
feeding an ever-expanding global population, especially in areas of Africa and Asia
where millions of farmers rely solely on rainwater for their crops. In Asia, 66 percent
of cropland is rain-fed, while 94 percent of farmland in sub-Saharan Africa relies on
rain alone, according to the International Water Management Institute (IWMI 2007 ).
These are the regions where water storage infrastructure is least developed and
where nearly 500 million people are at risk of food shortages.
There is no doubt that the changing pattern in the observed precipitation is the
signature of global climate change. That is, precipitation is being globally reallo-
cated by climate change. Perhaps it is the least developed that will experience the
most adverse consequences of climate change. Richer countries have now lived
with Third World poverty for decades and will view more disasters there, aggra-
vated by extremes of climate, as nothing new. The consequences of global warming