The influences of climate change have also covered Stung Chrey Bak Catchment,with increasing the significant issues over water demands for irrigation schemes. Thus, the aim of this research is to predict water demands of each irrigation schemes through climate change scenarios, using Water Evaluation and Planning model (WEAP). Stung Chrey Bak catchment consists of seven irrigation schemes. Two demand management scenarios were developed for this study –reference and 5 percent annual increase in irrigated area. To achieve this, SWAT model was used to generate flow discharge in each stream, command area and the irrigation demand for each irrigation scheme. As the result, water demand was reported enough for all scenarios in wet season. In contrast, the dry season rice meets water shortage especially in Tang Krasang for baseline scenario around 9262 m3 in January, 47752 m3 in February. In reference scenario, water scarcity occurred only in Tang Krasang, decreasing from 64547 m3 in 2014 to 51007 m3 in 2024. Moreover, if the farmers have continued to expand 5% of cultivated area, the irrigation water demand will highly increase from 27 million m3 in 2014 to 41 million m3 in 2025, causing unmet demand occurred in Tang Krasang, Chrey Bak, and Trapaeng Trabek. For climate change scenario B2 and A2, there is no water scarcity in both dry and wet season since water demands for agriculture are less than stream flow. In a situation of water limitation, water allowance between the three schemes facing unmet demands is very important for optimizing the use of water for agriculture. Cropping patterns should be applied for this situation, namely Chrey Bak scheme starting in early November and Trapaeng Trabek scheme in mid or late November in order to avoid an overlapping of irrigation peak demand.