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Irrigated croplands, mainly rice, in the watersheds of the In-
dus, Ganges, Brahmaputra, Yangtze, Huang He (Yellow River),
Tarim, Syr Darya and Amu Darya are all, to varying extents, de-
pendent on glacial water and snowmelt from the mountains
(Winiger
et al
., 2005). With rising temperatures, combined
with changes in the monsoon, up to 80% of the glaciated area
may be lost within this century (Böhner and Lehmkuhl, 2005;
UNEP, 2007).
While data are sparse in this region, actual observations from
Nepal indicate that current warming at high altitudes is oc-
curring much faster than the global average, up to 0.03º C per
year (Shrestha, 1999), and even faster at higher altitudes, up to
0.06º C per year (Liu and Chen, 2000; Eriksson
et al
., 2008).
Scenarios suggest that the effects on the rivers are highly vari-
able, ranging from a major increase in annual flow until around
2050 followed by a relatively rapid decline in flow for the Indus ,
to a gradual decline in flow in rivers such as the Brahmaputra. If
temperatures rise quickly, such as >0.06º C per year, the annual
flow of the rivers will invariably decline over time, particularly for
those dependent on the mountains, but less so for those more
dependent on the monsoons (UNEP, 2004; 2007).
The irrigated cropland in these basins, which are the most
dependent upon the mountains for water flow, comprises ap-
proximately 857,830,000 ha (UNEP, 2005; 2008). If average
production on irrigated rice is projected at 6 tonnes/ha (range
2–10 tonnes/ha), compared to 2–3 tonnes/ha for non-irrigated
land (combined, average about 3.3 tonnes/ha in Asia), the water
from the melting Himalayas annually supports the production
of over 514 million tonnes of cereals, equivalent to nearly 55.5%
of Asia’s cereal production and 25% of the world production
today. A reduction of, for example, 10–30% due to increased
flood damage to irrigated lands combined with reduced water
flow and seasonal drought, would thus lower world cereal pro-
duction of 3,000 million tonnes (by 2050) by 1.7–5%, even if we
assume no other yield increases in this period (in which case
losses would be larger).
Melting glaciers jeopardize Asian and world
food production