ARTICLE Features of the AFFRC model for evaluating the relationship between the water cycle and rice production Michiko Hayano Æ Naoki Horikawa Æ Tsuneo Kuwagata Æ Jun Furuya Æ Yasushi Ishigooka Æ Toshihiro Hasegawa Æ Tomoyuki Taniguchi Æ Akira Shimizu Æ Hitoshi Toritani Æ Minoru Tada Æ Takao Masumoto Received: 22 July 2007 / Accepted: 19 December 2007 / Published online: 22 January 2008 Ó Springer-Verlag 2008 Abstract This paper introduces the Agriculture, Forestry and Fisheries Research Council of Japan (AFFRC) model, an integrated model that predicts future rice production in the Mekong River basin by taking into account the effect of global warming on both the water cycle and the rice economy. The model focuses especially on the water bal- ance of paddy fields for different farmland water use systems. We defined six categories of irrigated paddies and three categories of rain-fed paddies on the basis of their systems of water usage. We included a process-based model to predict future rice production, accounting for daily changes in available water resources such as precip- itation. Many models of crop production treat rice in the same way as other crops; the particular characteristics of rice farming are considered in more detail in our model. Our results show that it is possible to estimate future rice production in the Mekong River basin by taking into account changes in available water, and to model the resultant effects on the grain market. Keywords Rice production  Rain-fed paddies  Irrigated paddies  Economic activities  Water cycle changes  Monsoon Asia  Mekong River basin Introduction In many parts of the world there are water resource problems caused by extreme changes to the water cycle. Among others, these include desertification, the disap- pearance of rivers, and the depletion of groundwater reservoirs. Water is an essential resource to meet growing demand for food production. Agriculture accounts for about 70% of all freshwater withdrawn from lakes, waterways, and aquifers around the world (e.g., FAO 2007). Water used for agriculture is a crucial component of the global water cycle. Global-scale changes in hydrolog- ical cycles, which are commonly expressed as changes in precipitation patterns, may restrict global water supply and thus undermine the stability of long-term levels of food supply and demand. Ten countries, of which nine are Asian, account for about 90% of world rice production (Masumoto 2004). The Mekong River is typical of Southeast Asian rivers; it runs through six countries (China, Myanmar, Thailand, Laos, Cambodia, and Vietnam) before debouching into the South China Sea. According to the World Meteorological Organization (Crop Explorer; http://www.pecad.fas.usda. gov/cropexplorer/), there are large regional and seasonal meteorological variations in the Mekong River basin. For example, mean annual precipitation within the basin varies regionally from 1,000 to 4,000 mm and the amounts of precipitation in the dry season and rainy season are sub- stantially different. The annual average flow of the Mekong River is 14,000 m 3 /s. During the dry season, the discharge M. Hayano (&)  T. Kuwagata  Y. Ishigooka  T. Hasegawa  H. Toritani National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba 305-8604, Japan e-mail: mhayano@affrc.go.jp N. Horikawa  T. Taniguchi  T. Masumoto National Institute for Rural Engineering, 2-1-6 Kannondai, Tsukuba 305-8609, Japan J. Furuya  M. Tada Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba 305-8686, Japan A. Shimizu Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba 305-8687, Japan 123 Paddy Water Environ (2008) 6:15–23 DOI 10.1007/s10333-008-0106-1