Agriculture Reference
In-Depth Information
However, even in the Asian monsoon region, water is not always abundant even in
the wet season, and unforeseen abnormal water shortages occasionally happen. At such
times, just as in arid and semi-arid regions, the absolute volume of moisture needed for
the growth of crops tends to be in short supply. Furthermore, “plot-to-plot irrigation”
tends to allows upstream farmers to have a strong priority in taking water. Most of the
downstream farmers with lower priority are reconciled to taking the drainage water
released from upstream paddy plots.
During abnormal dry spells, all water users want additional supplies of water. The
scarcity (i.e. value or shadow price) of water will temporarily soar in response to the
tightness of demand and supply of water. Good governance and equitable distribution of
water through Participatory Irrigation Management (PIM) is considerably important
during abnormal dry spells. It may be dangerous to leave the water distribution to market
mechanisms during abnormal dry spells because speculation and cornering may happen,
and disturb people's access to water.
2.3 Characteristics of paddy rice agriculture — multi-functional roles of water
use
Paddy field irrigation in the Asian monsoon region improves the utilisation efficiency
of water resources throughout the river basin, and contributes greatly to the formation of
healthy water cycles in river basins. In many instances, paddy field irrigation using this
ample water also has the “knock-on effects” of recharging groundwater; mitigating
floods; providing a domestic water supply and water for fish farming, shipping and other
industries; passing on traditional culture; protecting biodiversity; forming aquatic
landscapes; and other socio-economic effects and environmental services, in addition to
its benefits for agriculture. The functions that give rise to these benefits are generally
known as the “multi-functional roles of irrigation”. With paddy field irrigation in the
Asian monsoon region, these various socio-economic and environmental benefits are
relatively large. Therefore, these multi-functional roles are also characterised in that they
need to be correctly evaluated from the point of view of water use efficiency and
sustainability of PIM.
Masumoto (2003, 2004) comprehensively reviewed methodologies of quantifying
multi-functional roles of paddy field irrigation. He classified the multi-functional roles
into four groups:
water cycle control functions: flood prevention, groundwater recharge, prevention of
soil erosion, sediment collapse and landslides
environmental load control functions: water purification function, climate mitigation,
organic waste processing
nature formation functions: protection of biodiversity, landscape formation
social culture formation functions: health and recreation, relaxation.
He also introduced and interpreted some recent results of studies on quantification of the
multi-functional roles of paddy field irrigation more specifically. He pointed out that
attempts had been made to evaluate the multi-functional roles quantitatively. The specific
examples of these results were categorised as follows:
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