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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).

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