51
and that a similar estimate for the remaining irrigated lands
is considered an upper estimate, then the range of reduced
yields due to water scarcity is in the region of 1.7–12% of the
projected yield by 2050. Given the high dependence on many
of the world’s rivers for irrigation, this estimate could be quite
optimistic.
Except for the fact that glaciers are melting rapidly in many
places, we do not have adequate data to more accurately project
when and where water scarcity will affect irrigation schemes
in full. Making accurate projections is also difficult because of
variations in the effects on ground and surface water, as well
as on water for urban needs and industrial purposes Further-
more, the cost of water may also increase, seriously complicat-
ing the water scarcity question. Recent studies show that cost
of water has increased by about 400–500% since 1990 in the
Indo-Gangetic Basin of India.
Extreme weather events are also very hard to predict. Floods
and particularly drought can offset production gains and cre-
ate great fluxes in crop production, as well as in the survival
of livestock. Indeed, a higher frequency of extreme weather
events can have severe impacts on crop and livestock produc-
tion, particularly in Africa that appears especially vulnerable
Figure 21: Many of the largest rivers in the Himalayas Hindu Kush region are strongly dependent upon snow and glacial melt for wa-
terflow.
Indeed, some scenarios suggest a 20–90% increase in annual flow due to glacial reduction, followed by a 10–40% decline, as
glaciers and snow fall below critical thresholds for functions as water towers in 2050–2100. Combined with possible extreme precipita-
tion events, this may result in greater seasonal droughts, and damage from floods. (Source: Rees and Collins, 2004; UNEP, 2007).
������������������������������������������������
�����
�����
������
���������
���������
�������������
��
�������
����
��������
��������������
�������
���������
����
������
����
������
�������
���������
�����������
���������������������������������������������������
����������������������������������������������������������
���������������������������������������������������
����������������������������������
�����������������
����������������������
���������������������
����������������������������
����������������������������
����������������
���
���
��
��
����������������������
�
�
�
�
�
�
�
�
�