Paddy Field Characteristics in Water Use: Experience in Asia - Water and Agriculture: Sustainability, Markets and Policies - page 235

Paddy field irrigation using this ample water also has the “knock-on effects” or
“multi-functional roles” 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.
The water taken from a river and not consumed in paddy fields contributes to
enhancing ecosystem services in the Asian monsoon region in two ways: a) water in the
total paddy irrigation and drainage system serves as a network of wetlands and
waterways, and creates another excellent secondary natural environment outside the river
with an enriched flora and fauna; b) water drained from paddies and returning to the river
reinforces the ecosystems inside the downstream rivers, marshes and swamps. Almost
100% of the length of rivers in Japan has respectively been assigned, under the River Act,
an amount of minimum river flow for maintaining an appropriate downstream river flow
function for ecosystems, including bio-diversity.
Paddy field irrigation improves the utilisation efficiency of water resources
throughout the river basin, and contributes greatly to the formation of healthy water
cycles in river basins. The component ratio of return flow, embracing irrigated water and
rainfall in farm land, from upstream agricultural land increases as water flows
downstream, up to 35% at the lowest reach in the Kino River Basin in Japan. One the
other hand, 98% of the equivalent amount of intake water at Sanuki D.W. and 84% of that
at Okamoto D.W. return to the Kinu and Kokai River in Japan at several downstream
points.
Paddy fields provide a valuable habitat for living creatures because a combination of
shallow ponded warm water and fertile soil serves as an incubator and source of fodder
for living creatures. Furthermore, irrigation ponds connected with paddy fields through
canals, and scattered coppices and groves, provide another habitat and place of refuge for
living creatures during the non-irrigation period. Therefore, while the area of paddy
accounts for only 7% of the territory of Japan, more than 30% of all species of fish and
dragonflies and more than 20% of all species of reptiles, amphibians and plants survive in
paddy fields and canals in the surveyed 14 areas.
Groundwater recharge is another crucial function of paddy fields. Upstream paddy
fields of Kumamoto city in Japan supply 45% of the total groundwater recharge
(281 million tons) of which the city requires around 226 million tons annually for
drinking water, industrial water, and air conditioning for buildings.
5.2 Recommendations
Because the value, i.e. shadow price, of water is extremely low in normal times and
temporarily soars in response to tightness in the demand and supply of water, even in the
wet season, instead of water use efficiency in the normal condition, water use efficiency
during abnormal dry spells should be improved through promoting PIM in paddy field
irrigation in the Asian monsoon region.
Multiple socio-economic benefits and environmental services should be evaluated and
taken into account for designing government-oriented assistance (e.g. financial, legal,
institutional and educational services) for investment, rehabilitation and management of
water systems for rice, in order to achieve food security, poverty alleviation and
ecosystem conservation, which is difficult to maintain by a market approach.