Agriculture Reference
In-Depth Information
Ice Age Now 2011). In addition to the impact on glaciers, climate change may also
thaw the cryosphere and melt the permafrost of the Qinghai-Tibet Plateau (Cheng
and Wu 2007). Even with increasing risks of water scarcity due to glacial melting,
the water demand in South Asia is increasing very rapidly.
8.5 WATER RESOURCES AND THE RISING DEMAND
Water scarcity is a problem as old as civilization (Yeston et al. 2006). Globally, only
10% of the maximum available water and 30% of the green water (plant available)
is being used (Oki and Kanae 2006). The problem is the high variability (spatial and
temporal) and the uncertainties. The projected climate change exacerbates risks and
uncertainties (Sophocleous 2004) related to the severity of the water scarcity that
already exists. The renewable freshwater resources in arid and semiarid regions,
such as those in India and other South Asian countries, are likely to become more
unstable and prone to severe drought stress (Shen and Chen 2010). The problem of
drought stress on small landholder farms may be exacerbated by high risks of soil
degradation because of the widespread use of extractive farming practices and the
projected climate change.
Despite the abundance of renewable freshwater resources, the existing water scar-
city on a regional basis in India is also likely to be exacerbated with the projected
climate change. India receives an annual precipitation of about 4000 km
3
; however,
it has very high spatial and temporal variability (Kumar et al. 2005). For example,
Mousinram near Cherrapunji, in the northwestern region, receives the world's high-
est rainfall (~1250 cm/year). However, it also frequently suffers from a shortage of
water during the nonrainy season, every year (Kumar et al. 2005). The country as
a whole faces the problem of flood and drought syndrome, which may be accentu-
ated by the projected change in precipitation and temperature, overexploitation of
groundwater (see Section 8.6), water logging and salinity because of the excessive
use of canal water, salt water intrusion into aquifers of the coastal areas, and water
pollution/eutrophication and contamination.
South Asian rivers carry an annual water flux of ~2100 km
3
(~6% of global runoff)
and an annual sediment flux of ~1 billion Mg (~10% of global flux) (Subramanian
2008). High concentration of nitrogen (N) in waters of rivers in South Asia is
increasing because of intensive use of fertilizers in agroecosystems. The discharge-
weighted average of NO
3
-N in Indian rivers is 2 mg/L, and the average sediment-
bound N (mostly organic) is 0.2% (Subramanian 2008). In comparison, the reported
global average for the uncontaminated river system is 0.028 mg/L of NO
3
-N. The
concentration of NO
3
-N varies among rivers and locations in a river.
There is also contamination of groundwater with fertilizers, pesticides, and other
agricultural and industrial pollutants. In addition, arsenic (As) contamination in
groundwater in the Southeast Asia region is alarming, and >100 million people are at
risk (Rahman et al. 2009). The upper level of As concentration (μg/L) in the ground-
water has been reported at 4730 in Bangladesh, 1610 in Cambodia, 4440 in China,
3880 in West Bengal, 3191 in the Uttar Pradesh state of India, 3590 in Taiwan, 3050
in Vietnam, 2620 in Nepal, and 906 in Pakistan (Rahman et al. 2009). The accept-
able level for human consumption is 50 μg/L. Furthermore, the As-polluted water
