11.3.2.4. Tropical Asia
Agricultural adaptation to climatic variability is an evolving process. Planned
interventions through research, extension, or pricing or marketing policies
can have inadvertent detrimental impacts for poor farmers. Agricultural productivity
in tropical Asia is sensitive not only to temperature increases but also to
changes in the nature and characteristics of monsoons. An increase in leaf surface
temperatures would have significant effects on crop metabolism and yields, and
it may make crops more sensitive to moisture stress (Riha et al., 1996). Cropping
systems may have to change to include growing suitable cultivars (to counteract
compression of crop development), increasing crop intensities (i.e., the number
of successive crops produced per unit area per year), or planting different
types of crops (Sinha et al., 1998). Farmers will have to adapt to changing
hydrological regimes by changing crops. For example, farmers in Pakistan may
grow more sugarcane if additional water becomes available, and they may grow
less rice if water supplies dwindle. The yield ceiling must be raised and the
yield gap narrowed while maintaining sustainable production and a friendly environment.
Development of new varieties with higher yield potential and stability is complementary
to bridging the yield gap. Efficient production of a socially optimal level
of agricultural output in this region ultimately may depend on biotechnological
applications, but only if these applications prove to be environmentally sustainable.
Groundwater is the main source of freshwater in many parts of tropical Asia,
particularly in semi-arid regions. Water resources already are limited in terms
of supply and demand in this region. The aquifers in most countries have been
depleted by high withdrawal and low recharge rates, and significant drawdown
problems exist. Even with increases in precipitation, surface runoff may diminish
in some river basins under projected climate change scenarios because of greater
evaporation in a warmer atmosphere (higher hydrological elasticity). Increased
runoff in some river basins can cause deleterious effects such as greater flooding,
waterlogging, and salinity. More than 25% of the irrigated land in the Indus
basin already is affected by waterlogging and salinization (Hillel, 1991). Freshwater
availability in the coastal regions is likely to undergo substantial changes
as a result of a series of chain effects. Improvements in runoff management
and irrigation technology (e.g., river runoff control by reservoirs, water transfers,
and land conservation practices) will be crucial. Increasing efforts should
be directed toward rainwater harvesting and other water-conserving practices
to slow the decline in water levels in aquifers. Recycling of wastewater should
be encouraged in drought-prone countries in tropical Asia. However, major water
development decisions to augment water supplies may have greater relative hydrological,
environmental, and social impacts than climate change per se in the shorter
term. Climate change will affect the benefits to be accrued by future water
development projects and therefore should be taken into consideration in the
context of water resource policies and planning.
With rapid development of the economy in several countries in tropical Asia
during recent decades, the patterns of land use and land cover have been modified
significantly; a sequence of transitions and conversions is discernable. As
a result of different natural and socioeconomic conditions, the speed and scale
of land-use change is very diverse in different parts of Asia. This process
has contributed to significant losses in total forest cover; changes in standing
biomass and the soil carbon budget; extinction of mammals, birds, and vascular
plants; soil degradation; and threats to food security. Excessive human and
livestock population pressure in association with inappropriate agricultural
extension activities also lend an explanation for widespread land degradation
in tropical Asia. Salinization and acidification of soil in low-lying coastal
areas would adversely affect cropland in addition to land losses from permanent
inundation of deltas from anticipated sea-level rise.
Many of the major rivers originating in mountains and highlands are charged
with sediments, depending on the types of land uses in the watersheds (e.g.,
from forestry and agroforestry to open agriculture). Marginalization of production
areas in highlands will continue to increase soil losses, land slips, and slides
in the region. It has been suggested that upland micro-watersheds can be hydroecologically
sustainable only if good forest cover and dense forests are maintained (Rai,
1999). Under changing climate conditions, the pressure toward small- and large-scale
transfers of land for agricultural and urban uses may grow.
Sea-level rise poses the greatest threat and challenge for sustainable adaptation
within south and southeast Asia. The sea level already is rising in many locations,
primarily as a result of geological processes and anthropogenic manipulations.
Projected sea-level rise along the Asian coastlines represents an increase of
three to four times over present rates (Chansang, 1993; Midun and Lee, 1995;
Mimura and Harasawa, 2000). The potential impacts of accelerated sea-level rise
include inundation of low-lying deltas and estuaries, retreat of shorelines,
and changes in the water table (Wong, 1992; Sivardhana, 1993). Episodic flooding
from high storm surges would penetrate much further inland. Salinization and
acidification of soil in low-lying coastal areas will adversely affect agricultural
production, in addition to land losses from permanent inundation of deltas from
anticipated sea-level rise. The impacts will vary from region to region because
of local factors such as land subsidence, susceptibility to coastal erosion
or sedimentation, varying tidal ranges, and cyclonicity (Bird, 1993). The Ganges-Brahmaputra
in Bangladesh, the Irrawaddy in Myanmar, the Choo Phraya in Thailand, and the
Mekong and Song Hong in Vietnam are among the key low-lying river deltas in
tropical Asia that are most vulnerable to sea-level rise. Local-level social
and institutional adaptations in sensitive regions and development and promotion
of risk management can potentially prevent accelerated impacts to these deltas
through protection of the ecology of the region from further human interventions
so they can sustain themselves at least in a short time horizon.
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