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the calibrated model was executed to simulate the combined
effects of climate change and land use/land cover change to the
sediment yield of the Cagayan River Basin. The results of this
run are also shown in Figures 6a and 6b.
5.5. Model Simulation incorporating land cover-based
mitigation measures
The study used riparian reforestation and afforestation of hilly
and mountainous areas as two land cover-based mitigation
measures. Important SWAT input files (e.g., *.mgt, *.sol,
* hru) were modified to reflect these land cover changes. These
mitigation measures were applied to the model under the four
previously mentioned scenarios in Sections 5.1 to 5.4. Figure 7
shows the spatial distribution of HRUs where these mitigation
measures are applied while Figure 6b shows their effect on the
generated sediment yield of the basin.
6. ANALYSIS AND DISCUSSION OF RESULTS
6.1. The Effects of LULC and Climate Changes on the
Sediment Yield of the Cagayan River Basin
The Cagayan River Basin was found to have a total average
annual sediment yield of 114.76 ton ha! yr! under the base
Scenario that is, if the present land use/land cover (LULC)
distribution of the basin were to use in model simulation. This
simulated sediment yield agrees with the reported observed
range of average erosion rate for Regions CAR, I and II
according to FAO (1998) as cited by Asio et. al (2009). The
projected changes in LULC and climatic parameters have
produced an increase in sediment yield (+4.5% to +28.8%)
compared to the base scenario except for the climate change
scenario A2 2020. The said climate change scenario has
produced a decrease (-2.1%) in the basin’s sediment yield
possibly due to the projected lesser rainfall and less increase in
temperature compared to its counterpart for the year 2050 (A2
2050) and scenario A1B. It should be noted, however, that the
same scenario will eventually produce an increase in sediment
yield if coupled with LULC change (A220LC in Figure 6a).
In general, it has been demonstrated that sediment yield will
increase if the current LULC change rate and projected change
in the climatic parameters in the Cagayan River basin would
persist and climate change scenario AIB would bring a higher
increase in sediment yield compared to the A2 scenario.
6.2. Effects of Applying Proposed Mitigation Measures
The land cover-based mitigation measures applied to both
climate change scenarios with LULC change have produced
lesser sediment yields compared to the base scenario (Figure
6b) by about -26.3% to -45.32%. It is interesting to note that
the highest generated sediment yield (157.21 t ha yr! under
A1B50LC scenario) was decreased to 109. 44 t ha yr which
was lower than the current sediment yield of the basin (114.76 t
ha! yr!) under the base scenario. This demonstrated how
riparian reforestation and afforestation of hilly and
mountainous areas have successfully mitigated the ill-effects of
climate change to the sediment yield of the Cagayan river basin
even if coupled with LULC change.
7. CONCLUSIONS
The study has demonstrated how the integration of SWAT
model, Remote Sensing and GIS can be a powerful tool in
simulating watershed variables such as the sediment yield of a
large river basin. Moreover, the study has validated the
applicability of the model in simulating flow and sediment
discharge dynamics of the Cagayan river basin based on the
satisfactory values of the statistical measures of model
efficiency. Lastly, climate change data were successfully
utilized to quantify the impact of changes in the climate regime
to the sediment yield of the study basin.
REFERENCES
Alansi, A. W., Amin, M. S., Abdul Halim, G., Shafri, H. Z., &
and Aimrun, W. (2009). Validation of SWAT model for stream
flow simulation and forecasting in Upper Bernam humid
tropical river basin, Malaysia. Hydrol. Earth Syst. Sci. Discuss.,
7581-7609.
