Thailand's forests in reservoir watershed areas are declining at an alarming rate due to land use demand. Reforestation aiming at maintaining optimum forest areas becomes a top priority in reservoir management planning which needs hydrologic responses as inputs. This study aims at measurable assessment of the changes in hydrologic responses of the Ubolratana Reservoir in northeastern Thailand due to increasing forest areas. The assessment was done in two parts: (i) forest areas by CA Markov model and (ii) rainfall–runoff by Soil and Water Assessment Tool (SWAT) model. Assessment results indicate that increasing forest areas cause a decrease of runoff, peak flow, and hence, inflow volume into the reservoir. The optimum size of forest area was found to be much larger than the existing size, confirming the need for existing reforestation. Additional benefits of pursuing reforestation include less erosion and sedimentation which are required in reservoir management planning.

由于土地使用需求，泰国水库集水区的森林正在以惊人的速度减少。旨在维持最佳森林面积的重新造林成为水库管理规划的重中之重，需要水文响应作为投入。这项研究旨在对由于森林面积增加而在泰国东北部的Ubolratana水库的水文响应变化进行可衡量的评估。评估分为两个部分：（i）通过CA Markov模型进行的森林面积评估；（ii）通过土壤和水评估工具（SWAT）模型进行的降雨径流计算。评估结果表明，森林面积的增加会导致径流，峰值流量的减少，从而导致流入水库的流量减少。发现森林面积的最佳大小比现有大小大得多，这证实了对现有造林的需求。