## 3 Results and Discussion
### Water Demand Projection  
The projected water demand using the ensemble and RCP scenarios indicated the scheme will require more irrigation water in the future (with higher rate under RCP 8.5) in the months of March and September during dry and wet seasons, respectively (Figure 12). This is because in March (during the dry season), ISA III is pre-saturated plus normal irrigations for ISAs I, II, and III, which require larger irrigation amount. In addition, in September (during wet season), ISA III is pre-saturated together with ISAs I, II, and III under normal irrigations. In the other hand, a less water demand is observed from May to June in the dry season period and from November to December in the wet season. Normal irrigations is only observed in these periods, which require lesser irrigation amount. Figure 11: Flow duration curve for ensemble irrigation supply under RCPs with respect to baseline period of 1976–2005: (**a**) 2020s, (**b**) 2050s, and (**c**) 2080s. Figure 12: Projected mean monthly water demand from multi-models with three RCP scenarios for future periods of 2010-2039, 2040–2069, and 2070–2099 relative to baseline period of 1976–2005. The estimated water demand during dry season under multi-model projections based on RCP 4.5, 6.0, and 8.5 scenarios indicate an increasing trend of water demand, with a higher increase (11.09%) anticipated in the late century (2080s) under the RCP 8.5 scenario. The average changes in this season are 5.59%, -5.75%, and 10.71% for RCPs 4.5, 6.0, and 8.5, respectively. Increasing water demand in the dry season is attributed to the rise in temperature and decrease in seasonal rainfall. For RCP4.5 (RCP8.5) scenarios, water demand is expected to decrease 2.6% (6.2%) during the wet season, respectively. Although the temperature is expected to rise in the wet season, the reason for the decrease in seasonal water demand is due to a substantial contribution from the effective rainfall following the wet season Northeast Monsoon rainfall, which compensates for the warmer periods. Climate change may not significantly affect water availability in the countries of South-East Asia because water demand will decrease due to increased rainfall [53]. Throughout the dry season the water demand in the scheme will vary considerably in the future over the months, and the rise in effective rainfall during the wet season will compensate for the high demand for dry seasonal water. Therefore, no irrigation is needed in the months of May and June. However, the major challenge will be to manage the monthly variability in irrigation water demand in the target area properly, failure of which the irrigation system would lead to much greater uncertainty as the project is a run-of-the-river irrigation scheme with limited storage facilities. The project in Tanjung Karang Rice Irrigation is a run of the river (i.e., no water storage provided), which means the flowing water along the river to the scheme is either used or run as waste. Noticeably, the water supply to the scheme is not regulated based on the water demand. Irrigation supply is thus, observed to fluctuate along the seasons with over-supply in some periods and under-supply in other periods. It is projected that in future, the scheme would be over-supplied in January-February, May-June during dry season period, and November-December during wet season, with noticeable excess supplies in June and December (Table 3). However, from March-April in dry season and July-October (except October in 2050s and 2080s for RCP 6.0) in wet season, a shortage supply is projected based on the irrigation demand for RCPs 4.5, 6.0, and 8.5. Since the project is a run of the river, a recommended supply could be adopted, which enables a proportionate distribution of water among the tertiary canals through proper control of diversion headworks. For effective irrigation water management, a good balance between water supply and demand needs to be achieved.