KU-IWMI Seminar on Scientific Cooperation: 26 th March 2003. 1 1. Multi-Objective Optimal Planning of Land and Water Resources for Sustainable Small-holder Agriculture: Case Study in the Mae Klong River Basin, Thailand M. Mainuddin 1 , B. Kwanyuen 2 and S. Sangunurai 1 1 IWMI Southeast Asia Regional Office 2 Assistant Professor, Dept. of Irrigation Engineering, Kasetsart University. Email address of corresponding author:m.mainuddin@cgiar.org 1. Introduction More than ever before in the course of human history, the way in which land is being used has become a source of widespread concern. The population of the world surpassed 6 billion; hence, never before in history have that many mouths to feed (Van Keulen et al., 2000). In Asia, populations will continue to increase sharply between now and 2025. (Roetter et al., 2000). This increase in population in urban and rural areas continues to exert pressure on natural resources with an increased focus on productivity in order to attain food security. On the other hand, competing demands from urban, industrial, and recreational interests are imposing increased pressure on agriculture for efficient land and water use. With these ever-increasing demands, the need for improved management of available land and water resources is of utmost importance. Optimization of resource management considering the multiple goals, priorities, and constraints, using state-of-the-art data generation and estimation techniques including simulation models and expert knowledge can contribute significantly to the sustainable management of resources. This form of optimization is usually done on a much larger scale and often details at the field and community level are either ignored or aggregated. Medium- to long-term plans and targets selected by local or national governments scenario analysis or other methods aiming at regional-scale analysis, have little direct impact on farmers. Farmers make decisions about land management of a short- to medium-term nature, whereas policymakers make medium  to long-term decisions. They do achieve these using different sets of information and objectives. Farmers will respond to these plans when they are translated into better markets, better credit systems, improved information, etc. When optimization models are applied to whole basin, land units are largely of the order of 1 to 10 km 2 , meaning that there is still much variability in site- and situation-specific conditions. In addition, every farm household has different sets of resources at their disposal with respect to land, water, equipment and labor, capital and education. Farmers therefore still have the challenge of making many appropriate decisions. The better government planning and subsequent translation into improved socio-economic conditions, the faster farmers see returns for their investments (Penning de Vries, 2000). IWMI with KU has initiated a study under Theme 1 titled Developing a proto-type procedure for multiple goal analysis for allocation of land and water resources of river basins: Case Study on the Mae Klong River Basin, Thailand. The purpose of this project is to develop and test a proto-type decision support system (DSS) that can be used for river basin analysis to explore possible land and water resources management options considering land and water as a limiting resources. Such decision tools will be useful in evaluating development scenarios among different stakeholders taking into account the priorities as well as the constraints and opportunities for the use of natural resources. The development scenarios for river basin planning do not take into account the variability in the biophysical and socio-economic conditions at the farm or community level, which may adversely affect smallholders and poor farmers. In this study, multiple goal linear programming procedures will be used at the farm or village level considering the on-farm and household details in one or two representative water and land evaluation units (the smallest unit for optimization at river basin scale). The effect of the development scenarios (for the river basin) will be analyzed and alternatives will be developed to minimize these effects. The purpose of the study is therefore, to develop sustainable land