Summaries (En) | Gift

Summary (En)

Summary (En)

At first glance, it appears that the region is well endowed with water resources. While accounting for only about 16 percent of the world's land surface, it receives 22 percent of its precipitation and produces 28 percent of its renewable water resources. However, the region is home to 53 percent of the world's population and its IRWR [internal renewable water resources] are only about half of the world's average. By and large, most countries in Asia (except for Singapore, Maldives and Republic of Korea) are still not considered water-stressed. However, even in countries with high level of per capita water availability, large segments of the population are beset with water scarcity as a result of the large variations in the spatial and temporal distributions of rainfall and stream flow. About 84 percent of the total water withdrawal of the region is for agriculture. Irrigation accounts for the bulk of water use in agriculture due to the large irrigation base and the fact that approximately half of the irrigated area is devoted to flooded rice production. Although still relatively small in most Asian countries, the industrial, municipal and environmental demands for water continue to increase at a rate twice that of population growth. The proportion of water available for agriculture is projected to decline to 62 percent worldwide and 73 percent in developing countries by 2020. Hence, the opportunities for expanding the irrigation base are limited. If food security is to be maintained, ways of increasing water productivity must be found. A host of interrelated issues must be addressed in the short-and-medium terms if a water crisis in the region is to be averted. Among others, these include: changing demand patterns, impact of climate change and watershed modifications on dependable water supply, low water productivity in agriculture,in adequate investments in water supply systems to meet future demands, a shift toward decentralized and privatized water service and market mechanisms, the need to reduce non-revenue water, sustaining and expanding the irrigation base, recycling wastewater for agriculture, access to water of the rural and urban poor, groundwater mining, the need to strengthen international collaboration for managing shared water resources, protection of freshwater ecosystems, and fostering a favorable environment for a comprehensive water resources policy and program frameworks. The specific issues in irrigation that are more pressing were discussed. Suggestions on how to address these issues were presented. Two very significant changes in irrigation development policy and strategy in many developing countries of Asia were discussed. First is the shift from large, gravity irrigation systems towards small privatized farmer-controlled irrigation systems such as shallow tubewells, low-lift pumps, farm reservoirs and diversion dams. Second is the dramatic shift from the virtual monopoly of the central role of national government towards greater participation of other players such as WUAs [water users association], NGOs [non governmental organizations], and local government units. The public sector activities are now focused on improving the management of water at the main system level and adopting new policies aimed at creating incentives for WUAs or cooperatives to take over the O and M [operation and management] of the rest of the irrigation facilities.

For the purpose of examining on role of irrigation and cultivation system to paddy ecosystem, we study species and number of Odonata larvae and analyze the stable isotope ratios of the Odonata larvae and the plankton/detritus in water of paddy fields and irrigation ponds. As a results, cultivation system clearly effects to composition of species and number of Odonata larvae. delta sup(13)C indicates that Orthetrum albistylum speciosum larvae and Coenagrionidae spp. larvae which are dominant species in paddy water, depend on specified food sources, each other. delta sup(15)N shows that the trophic level of Odonata larvae is higher than that of the plankton/detritus in paddy water. It is considered that analyze the stable isotope ratios application is effective to examine water ecosystem and food web in paddy.