# 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  
#### 3.3.1 Hydro-Meteorological Variables  
In the paddy water demand model, effective rainfall is an important factor for estimating the daily water requirements. Effective rainfall is a fraction of total rainfall received that can be used directly in the paddy field after losses due to runoff and deep percolation. To optimize the use of rainfall and save irrigation water for future usage, a reasonable estimation of future seasonal effective rainfall is therefore necessary. Changes in effective rainfall are substantially different with the GCM and RCP scenarios with no consistent pattern (Table 2). The Commonwealth Scientific and Industrial Research Organization (CSIRO) and Hadley Global Environment Model 2-Earth System (HadGEM2-ES) models show a substantial decrease in effective rainfall, while the Max Planck Institute-Earth System Model running on low resolution grid (MPI-ESM-LR) and Canadian Earth System Modelling (CANESM2) models forecast a notable increase. The change in effective rainfall, therefore, is not necessarily defined by the characteristics of a certain model, rather, it largely depends on its physical parameterization. These variations underline the inherent uncertainty of GCM forecasts on climate models. Analysis of simulated annual rainfall from different GCMs by [41] also found that each GCM exhibits a large spread of the annual rainfall. Predicting effective rainfall is thus a potential source of uncertainty in impact assessments. The model outputs reveal that future effective rainfall will decrease from the baseline period by an average of 9.39%, 34.33%, and 17.90% for RCP 4.5, RCP 6.0, and RCP 8.5, respectively, using the multiple models in the dry season period (Figure 3). There is a noticeable decrease of 38.47% (27.01%) in RCP 6.0 (RCP 8.5) in the latter part of the century (2080s) for the worst-case scenario (RCP 8.5). In Figure 3, the decrease is pronounced in March, April, May, and June. However, the season is wetter in April, May, and June during later future periods (2050s and 2080s). This indicates that future dry seasons might be wetter than the current dry season. This predicted rainfall might militate against the conditions of drought that currently often affect paddy schemes. In the wet season, effective rainfall is projected to respectively increase 3.46% (5.55%) for RCP 4.5 (RCP 8.5); for RCP 6.0 rainfall is expected to decrease (by 9.79%). However, in both seasons, the RCP6.0 scenario shows a different trend, projecting a higher rate of decrease in the dry season and an increase in the wet season in all future periods. This might be due to the lack of data available for this scenario in some GCM repositories (Table 2). Climate projections in the study location, therefore, show a decrease in the effective rainfall of the dry season (January-June) and an increase in the wet season (July-December). Based on these findings, flooding is likely to increase during the wet (main rice growing) season, as well as intermittent dry spells during the dry season. This difference in rainfall in both seasons needs to be taken into account in the scheme's water resource planning.