A thesis submitted in partial fulfilment of the requirement for the degree of Master of Engineering, School of Environement, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1982

In this study, a computer model for assessing the potential of rainfed agriculture has been further modified from the previous AIT study. The development of the model is based on water balance and it consists of two submodels, for generating daily rainfall and evaporation. For the generation of daily rainfall, it includes three different frequency distributions so that the model could be more flexible. The second submodel is used for generating daily evaporation in which the Thomas-Fiereing model was selected for preserving the mean, standard deviation and serial correlation. A comparative study between pan evaporation and potential evapotranspiration estimated by the Jensen-Raise Formula, Radiation Method and Penman Method has been carried out in this study. A daily pan factor as estimated by the Penman Method has been applied for ten stations of Thailand . Subsequently, the potential evapotranspiration can be easily estimated by Pan Evaporation Method, In order to make the model more comprehensive and applicable in the estimation of every variable needed for the assessment of the potential of rainfed agriculture for different regions, the effect of different soil types and crops are incorporated in the water balance analysis.