## 3 Proposed Methodology
### Case Study  
The agricultural sector in Thailand is mainly located in the northern part of the country, with Tak City as one of the agricultural areas. Tak City is the capital of Tak Province, situated in western Thailand, 492 km from Bangkok. One of their primary industries is the agricultural sector. According to data from the Central Agricultural Registration Database System of the Ministry of Agricultural Extension in 2020, the top five products produced in Tak City are corn, rice, cane, cassava, and rubber, as shown in Figure 2[35]. Tak has a tropical savanna climate, where winter is dry and warm, and summer can reach up to 37 \({}^{\circ}\)C [36]. The average rainfall throughout the last decades has been varied, with the highest during July and August, as shown in Figure 3. As part of its development, the need to have better farming management in Tak City increases. In the Tak City case, some agricultural products are not rainfed and depend much on irrigation water. That being said, irrigation management is needed to enhance the productivity of small farmers and ensure that those small farmers can gain access to water resources.  
Figure 3: Average Monthly Precipitation and Temperature (1981–2010) (Plotted from: Thai Meteorological Department, 2018 [36]).  
Figure 2: Tak City Agriculture Product Yield Percentage in 2020 (Plotted from Central Agricultural Registration Database System Ministry of Agricultural Economics Thailand, 2020 [35]).  
Irrigation management aims to give the proper amount of water to the crop according to their necessity. Irrigation management should yield both quality and quantity of the crops based on the type of crop, type of soil, and water availability. The timing for water irrigation is also important to achieve optimum production. Nonetheless, the need for better agriculture management is not limited to only irrigation management. Due to climate changes, the rainy season period is shifted, and thus analytical water forecasting needs to be conducted before planting the crop. The result of the water forecast also helps the type of crop that should be planted and how the water should be distributed, respectively. The type of soil and water availability can help farmers decide the type of crop they will plant in certain areas. Nevertheless, as the problems lie in the limitation of soil nutrients and water for better crop yields, the decision support system (DSS) is needed to manage and optimize those limitations.  
In Tak province, Huay Mae Thor reservoir withholds 63,000,000 m\({}^{3}\) and supplies water for many uses, especially agriculture. This amount of water can provide about 51,200,000 m\({}^{2}\) of agricultural area. However, only 6,640,800 m\({}^{2}\) are provided by the reservoir. Six gates connecting the river and the reservoir control the water to the agricultural area in six zones shown in Figure 4. The average amount of water from 2016 to 2020 is about 42,000,000 m\({}^{3}\), illustrated in Figure 5. The DSS is applied to crop planning and irrigation management in the case study of Huay Mae Thor reservoir, Tak Province, Thailand. Six areas/zones are considered in the experiment, where the water from the reservoir is supplied to the agricultural area shown in Table 1.