Water availabllity varles tremendously across countries, ranging from 1,428 m³/ cap/yr in the Republic of Korea to 58,632 m³/cap/yr in Laos (see Table 3). Acco rding to Rosegrant and Meinzen-Dick (1996) countries with fresh water resources ranging from 1,000 to 1,600 m³/cap/yr face water stress, with major problems i n drought year. Countrles are also considered water scarce when intemal renewab le water resources are less than 1,000 m3/cap/yr; below this threshold, water a vailability becomes a severe constraint on socio-economic development and envlr onmental quality (Engleman and LeRoy, 1993). These aggregate, country-level ind icators of water availability may differ from the specific vari-ability in wate r resources by region, Iocality, and season in each country. Chen and Ji (1995) reported that annual rainfall in Chlna has decreased from 1,600 mm/yr in the s outheastern coastal regions to less than 200 mm/yr in the northwestern reglon. Rainfall has become more irregularly dlstributed, causlng drought, flashfloods, and waterlogging. Likewlse, the monsoonal rains in Southeast Asia have been ir regular during the last five years, particularly in the Indochina peninsula.

Large irrigation schemes by upstream waterwork development of large river in th e Asia-Pacific countries did contribute to higher production of food grain and electricity, but on the other hand, they also cause adverse effects on the down stream areas, most readily felt In the Mekong Delta where salinity intrusion an d impounded acld water during the dry season become a hindrance to agriculturc production.