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ECOSYSTEM RESTORATION
FOR WATER SUPPLY
Mountain regions all over the planet are crucial water towers:
Indeed, the Hindu Kush Himalayas supply water for over 55%
of Asia’s cereal production or near 25% of the Worlds cereal
production (UNEP, 2009; UNEP 2010). Increased irrigation
schemes were a key component of the former Green revolu-
tion in Asia, and 70–90% of the world’s water consumption is
indeed consumed by irrigation (UNEP, 2009; 2010). Riparian
vegetation helps buffer erosion, prevents and mitigates agricul-
tural run-off, while trees, shrubs and plants are crucial in hin-
dering erosion of hill slopes and the loss of nutrients.
Meandering rivers and wetlands serve not only to slow speed of
water, but also to allow gradual sedimentation of organic mat-
ter, sediments and create spawning habitat for fish and habi-
tats for amphibians and reptiles, insects and birdlife. Wetlands
have been estimated to provide ecosystem services of a value
of around 5,000–20,000 USD/ha/year (Costanza
et al
., 1997;
Zhao
et al
., 2005; both in 2010 USD) or globally over 6,615 tril-
lion USD per year.
In some regions, diversion of water for agricultural and other
purposes has reduced river flow to drylands, coastal areas, with
Forests play a key role in global water supply. At present 75% of globally usable fresh-
water supplies come from forested catchments (Fischlin
et al
. 2007), therefore water
is critically linked to forests in much of the developing world. Forests are also crucial
for flow regulation and in hindering flash-floods from water originating in mountains
or in extreme rainfall events (UNEP, 2004; 2010, in press). This is crucial in terms of
providing predictable water supply to crop areas, such as through retention of water in
wetlands and forests buffering both droughts and floods (Bruijnzeel 2004; UNEP, 2005;
ICIMOD, 2009). Forests also have a key function in climate regulation through influenc-
ing weather and rainfall, as well as in capturing rain- and mist water, such as in cloud
forests (UNEP-WCMC, 2004) and in filtering water.
severe impacts on these drylands, coastal habitats and estua-
rine-dependent species. For example, damming of the Colo-
rado River has drastically changed what used to be an estuarine
system into one of high salinity and reduced critical nursery
grounds for many commercially important species including
shrimp (Aragón-Noriega and Calderon-Aguilera 2000).There
are many well-documented examples where diversion of wa-
ter for agriculture has degraded and reduced the extent of in-
land water bodies (e.g. Aral Sea and Tarim river, China)(UNEP,
2004), affecting fish spawning and migration and causing a
collapse of the fishing industry and a loss of species diversity
(MA 2006). Intensifying agriculture also erodes ecosystem
services: From 1961 to 1999 the area of land under irrigation
nearly doubled; the use of nitrogenous and phosphate fertiliz-
ers increased by 638% and 203%, respectively, and the produc-
tion of pesticides increased by 854% (Green
et al
. 2005), and
improving irrigation efficiency is crucial to restoring ecosystem
services (Crossman
et al
., 2010).
Restoration towards securing water supply and filtering must,
however, not only take into account trees and riparian vegeta-
tion, it must also address the naturally occurring species and