Paddy Field Characteristics in Water Use: Experience in Asia - Water and Agriculture: Sustainability, Markets and Policies - page 209

Chapter 15.
Paddy Field Characteristics in Water Use:
Experience in Asia

Kazumi Yamaoka 1

Typical arguments at international water fora advocate a competitive relation between
agricultural water use and other water use, including for ecosystems. This premise is
generally applicable to the discussion on irrigation in arid and semi-arid regions where
water is constantly scarce. However, it is unsuitable for humid regions such as the Asian
monsoon region where paddy rice culture has been developed for thousands of years,
using ample natural water from rainfall, including flooded water and artificially irrigated
water from various water sources such as streams, ponds and rivers. The inundated water
in paddy fields and flowing water in irrigation and drainage canals serves as a network
of wetlands and waterways to create another excellent secondary natural environment
outside the river. Furthermore, paddy fields stretching along a river serve as a retardant
reservoir that at once receives outflow from the mountainous hinterlands and irrigated
water drawn from the river, and that gradually supplies the water to groundwater
aquifers and the downstream river. This paper, in the context of the impact of irrigation
on the environment, reviewing studies and reports of recent years on quantifying
hydrological characteristics on a basin scale and identifying services for secondary
natural environment in Japan, shows the unique natural features and cultural climate in
paddy field irrigation in humid regions contrasting with those in irrigation in arid and
semi-arid regions. It also describes international activities among rice growing countries,
regions, international organisations and research institutions, namely the INWEPF, and
the Japanese policy direction “Shifting to agriculture, thinking much of preservation of
the environment”, and gives recommendations for future challenges.

1. Introduction

Although Asia accounts for only 24% of the world's land area, it holds more than
60% of the world's population of about six billion. About 54% of the world's population
live in a region known as humid Asia, or the Asian monsoon region, that covers only
about 14% of the world's land area. Arable land in Asia, producing food to sustain this
population, accounts for only about 34% of the world's arable land area of about
1. National Institute for Rural Engineering (NIRE), Ibaraki-ken, Japan.