## Materials and Methods
### Modeling Future Impacts of Climate Change on Hydrological Processes  
A recent version of hydrologic modeling software developed by the U.S. Army Corps of Engineers Hydrologic Engineering Centre (HEC-HMS 4.2.1) was used for simulating precipitation-runoff processes of upper Bernam watershed systems. The model requires two types of data: the spatial and climatic data. The spatial data used include digital elevation model (DEM), downloaded from Geographic information software program (DIVA-GIS) website, maps of soil and land use of the area obtained from Department of Agriculture (DOA) Malaysia while daily archives of the hydro-climatic data from 1976-2006, obtained from the Water Resources and Hydrology Division, Department of Irrigation and Drainage (DID) Malaysia, which include rainfall, temperature (minimum and maximum), relative humidity, wind speed and solar radiation were used. The HEC-HMS model components include basin models, meteorological models, control specifications, and input data. The components were used to simulate the hydrologic response in the Bernam watershed. The spatial data collected was used to set up the basin model using HEC-GeoHMS to calculate parameters, such as sub-basin areas, times of concentration, lag time, and reach lengths based on the DEM geospatial information. The hydrological elements consist of sub-basin, reach, junction, sink (outlet), and diversion within the watershed as shown in Figure 4. Land use map of the area was processed into eleven classes. These include Aquaculture, Forest, Marshall, Oil palm, Paddy, Pasture, Rubber, Secondary forest,  
Figure 3: Windows for downscaling climatic variables time-series (2010–2099): (**a**) downscaling daily rainfall generation and (**b**) downscaling meteorological variables. Swamp forest, Urban, and Waterbody. The size of the land use classes of Bernam catchment ranges from 0.2 to about 41% with the largest area dominated by forest followed by Oil Palm then Rubber. Moreover, the forest area contributed more for the impervious surfaces in the watershed followed by Oil Palm area then area covered by Rubber. Impervious area is a portion of the watershed for which all contributing precipitation runs off, with no infiltration, evaporation or other volume losses. This is expected considering the nature of the land use within the watershed, which is majorly forest and oil palm. Similarly, the soil was classified into two major hydrologic soil groups, namely groups B and C. About 84% and 16% of soil groups B and C, respectively dominate the soil in Bernam watershed. The group B soils typically have from 10%-20% clay and 50%-90% sand, and have loamy sand or sandy loam textures, with moderately low runoff potential when thoroughly wet. Whilst group C soils typically have from 20%-40% clay and less than 50% sand and have loam, silt loam, sandy clay loam, clay loam, and silty clay loam textures with moderately high runoff potential when thoroughly wet. This means less runoff amount is averagely expected in the area. The sizes of the merged sub-basins range between 160.49 km\({}^{2}\) and 370.32 km\({}^{2}\). Land use and soil grids were processed to obtain percentage of impervious area, maximum deficit, initial deficit and constant rate of each sub-basin as presented in Table 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sub-Basin No.** & **Area (km\({}^{2}\))** & **Initial Deficit** & **Maximum** & **Constant Rate** & **Impervious** \\  & **(mm)** & **Deficit (mm)** & **(mm/h)** & **Surface (\%)** \\ \hline
1 & 325.38 & 50.46 & 52.50 & 48.45 & 2.51 \\
2 & 370.32 & 47.64 & 51.65 & 49.50 & 4.28 \\
3 & 160.49 & 50.55 & 51.50 & 50.50 & 5.10 \\
4 & 261.10 & 49.43 & 50.36 & 48.44 & 3.83 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristics of delineated sub-basins of Bernam watershed. Figure 4: Hydrologic Engineering Corps Hydrologic Modeling System (HEC-HMS) model development processes for upper Bernam river watershed: (**a**) basin merge, (**b**) basin river network, (**c**) HMS-node, and (**d**) HMS basin model.