# Climate-Smart Agro-Hydroological Model for a Large Scale Rice Irrigation Scheme in Malaysia
## 3 Results and Discussion
### Modeling Streamflow under Climate Change Impacts  
Figure 7 shows an example of average future changes in seasonal streamflow under multi-model projections based on RCP 4.5, 6.0, and 8.5 scenarios relative to the baseline period (1976-2005). The average changes for RCP 4.5, 6.0, and 8.5 are \(-\)0.40%, \(-\)1.68%, and \(-\)5.71%, respectively, during the dry season (Table 4). The model outputs suggest a decreasing pattern in streamflow in this season for all future periods, with a higher rate (\(-\)5.94%) expected under the RCP8.5 scenario in the latter part of the century (2080s). A similar change pattern is observed in the wet season, however, with a lower rate, except for RCP4.5, in which it is expected to increase (0.36%). The model output, therefore, highlights the changes in future streamflow at Bernam river basin to be more pronounced during the dry season period. This might be associated with the warmer temperature during this period, which consequently affects the future streamflow. The available water for supply to the scheme largely depends on the streamflow at the basin outlet. A significant change in the future streamflow translates to the available irrigation supply. Therefore, the scheme is predicted to experience water shortages, particularly during the dry season period. This would consequently affect the water resources in the scheme, which could lead to negative impacts on the overall crop production in the area. A similar decrease in annual streamflow was observed by [4] and [5]. Although the changes in streamflow are not great, the basin may suffer from reduced water pressure, particularly during the dry season period.  
Projection of Available Supply for Irrigation  
The projected available water for supply to the scheme, which largely depends on the streamflow from the Bernam basin, would decrease in both dry and main seasons in all future periods, with a noticeable decrease (\(-\)12.57%) in the latter part of the century (2080s) for RCP 8.5 during the dry season (Figure 8). The average changes for RCP4.5, 6.0, and 8.5 are \(-\)7.94% (\(-\)7.86%), \(-\)10.30% (\(-\)9.84%), and \(-\)12.42% (\(-\)12.26%) during the dry (and main) seasons, respectively. The model outputs reveal that the decrease in available water for supply would be higher during the dry season period. This might be due to the decrease in rainfall and warmer temperatures during the season, which increase the rate of evapotranspiration more compared to the wet season period, and consequently affect the future available supply. Therefore, the model could be integrated with adaptive cropping patterns to enhance future water allocation. Since the project is a run-of-the-river project, a recommended supply could be  
Figure 7: Projected mean monthly streamflow from multiple models for three RCP scenarios (RCPs 4.5, 6.0, and 8.5) for three future periods of 2010–2039, 2040–2069, and 2070–2099 relative to the baseline period of 1976–2005.  
adopted that enables proportionate distribution of water among the tertiary canals through proper control of the off-take structure gate. A factor can be introduced (considering the rice's water-sensitive growth stages) to achieve an equitable supply. The factor depends on the management and operational decisions in the command area with respect to the available water for irrigation. With the advance of the irrigation season, the recommended irrigation supply (allowable supply based on available water) for tertiary canals is proposed.