# Climate-Smart Agro-Hydroological Model for a Large Scale Rice Irrigation Scheme in Malaysia
## 3 Results and Discussion
### Climate-Smart Agro-Hydroological Model Simulation Outputs
#### 3.3.3 Impact on Potential Evapotranspiration  
Potential evapotranspiration (ET\({}_{0}\)) is a key element in computing and scheduling of irrigation requirements. Climate change affects all climatic parameters, including ET\({}_{0}\). Values of ET\({}_{0}\) were computed based on downscaled meteorological variables using the FAO-56 Penman-Monteith method. The average maximum and minimum temperatures for the three scenarios of the RCP continue to rise during the 2020s, 2050s, and 2080s over the baseline period. In all GCM models, the probable rise in temperatures in each of the three emission scenarios is generally agreed. This means that in future, and particularly in dry season months, the scheme will be warmer. The findings of the Intergovernmental Panel on Climate Change (IPCC) for Southeast Asia show a similar pattern in the future [45]. According to RCPs 4.5, 6.0, and 8.5, the ET\({}_{0}\) will increase over the coming three periods by 1.6%-3.7%, 0.8%-4.7%, and 1.6%-9.1%, respectively. In the dry season (March-July), the monthly ET\({}_{0}\) rises are prominent (Figure 4). RCP 8.5 (most extreme) in the 2080s at 14.2% and RCP 6.0 at 0.2% are the most significant increases.  
The study shows clearly that the expected increase in temperature directly impacts the irrigation requirements. Figure 5 indicates that there will be increased irrigation needs in the future. Climate-smart adaptation approaches are therefore crucial to meet demand for crop water under future climatic conditions.  
The three possible RCP scenarios would theoretically result in a change in the monthly temperature according to the projection. RCP8.5 predicts a substantial increase in temperature every year with an average temperature of between 3.5 \({}^{\circ}\)C and 3.7 \({}^{\circ}\)C. More warming is expected over the wet season compared to the dry season in the irrigation system (Figure 6). Based on the GCM results, more water will be needed in future, except for the months of October and November. The reference evapotranspiration will rise in future periods as a result of the warming trends resulting from temperature increases.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Period** & \multicolumn{3}{c}{**Changes in Temperature under RCPs**} \\ \hline  & **RCP4.5** & **RCP6.0** & **RCP8.5** \\ \hline Maximum temperature (\({}^{\circ}\)C) & & & \\ \hline
2020s & 0.68 & 0.52 & 0.82 \\
2050s & 1.29 & 1.06 & 1.85 \\
2080s & 1.57 & 1.85 & 3.25 \\ Average & 1.18 & 1.14 & 1.97 \\ \hline Minimum temperature (\({}^{\circ}\)C) & & & \\ \hline
2020s & 0.71 & 0.62 & 0.92 \\
2050s & 1.36 & 1.16 & 1.95 \\
2080s & 1.75 & 1.85 & 3.36 \\ Average & 1.27 & 1.21 & 2.08 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Projected changes in temperature under multi-model projections based on RCP scenarios relative to the baseline period of 1976–2005.  
Figure 4: Projected mean monthly ensemble of multi-model reference evapotranspiration (ET\({}_{0}\)) for RCP4.5, RCP6.0, and RCP8.5 scenarios and future periods of 2020s, 2050s, and 2080s compared to the baseline period.  
Figure 5: Projected multi-model annual reference evapotranspiration (ET\({}_{0}\)) for the RCP4.5, RCP6.0, and RCP8.5 scenarios from 2010 to 2099.  
Figure 6: Projected monthly multi-model effective rainfall (ER) and reference evapotranspiration (ET\({}_{0}\)) for RCP scenarios in future periods (2010–2099).