RESULT AND DISCUSSION 1 Land cover changes

Bogor, 21-22 October 2015 657 3. RESULT AND DISCUSSION 3.1 Land cover changes In 2009, Citanduy Hulu sub-watershed was dominated by paddy fields 29 and mix gardens 26. While a total of forest land cover protected forest, limited production forest was 20.73 Table 2. The scenario of 30 forest land cover is constructed from land cover changes of limited production forest and some of the mixed gardens Table 2 and Figure 2. While the scenario of 70 agroforestry land cover is constructed from land cover changes of forests, shrubs, mixed gardens, dry land agricultures and paddy fields. Table 2: Condition of the existing land covers in Citanduy Hulu sub-watershed and the land cover changes in each scenario No. Land cover types Luas Ha Existing condition 2009 30 forest 70 agroforestry 1. Shrubs 553.8 553.8 2. Limited production forest 1 887.9 8,143.5 3. Limited production forest 2 4,974.3 4,974.3 4. Protected forest 9,146.7 9,146.7 5. Settlements 7,730.3 7,722.3 7,722.3 6. Mix gardens 18,543.3 11,295.8 7. Paddy fields 20,676.1 20,676.1 14,239.9 8. Ponds 12.7 12.7 12.7 9. Body of water 420.5 420.5 420.5 10. Dry land agricultures 9,462.5 9,462.5 11. Swamps 1.3 1.3 1.3 12. Agroforestry 50,012.8 T o t a l 72,409.4 72,409.5 72,409.5 3.2 Calibration and verification Calibration aims to determine the value of a parameter group so that simulation results of discharge model closer to the actual discharge value. While verification is used for evaluate the ability of the model whether closer to the actual watershed conditions. Evaluation of the ability of the model applies statistical criteria. The statistical method which has been used is the percentage of differences between observation value DVI and Nash-Sutcliffe coefficient ENS. If the mean simulation discharge is about -15 till 15 of the mean observation discharge, E NS values ≥ 0.5 and R 2 ≥ 0.6, it is included in good criteria Santi et al., 2001. For calibration process and verify the model is used discharge data from Sindangrasa station. Data from Januari-June 2009, is used for calibration process and data from July-December 2009 is used for verify the model. The calculation for Nash-Sutcliffe coefficient ENS is 0.76, Dv = -14,96 and R2= 0,79 for relationship between prediction discharge X and observation discharge Y. Bogor, 21-22 October 2015 658 Figure 2: Land cover existing, scenario of 30 forest land cover and Scenario of 70 agroforestry land cover 3.3 Hydrological condition 3.3.1 Hydrological condition of Citanduy Hulu sub-watershed The mean annual evapotranspiration, runoff, lateral flow and baseflow of Citanduy Hulu subwatershed is 66.1 mm 23, 121.6 mm 43, 83.3 mm 29 and 50.0 mm 18, respectively. The annual rainfall varies between 2,794.5 to 3,429.2 mm.The simulation indicates that river discharge is getting low and evapotranspiration is getting high Figure 3. Based on the land cover existing condition, there is an increase trend of water yield derive from lateral flow and base-flow contribution, meanwhile runoff contribution tends to decrease. Furthermore, the analysis explains when the discharge and rainfall increase, the lateral flow and baseflow also increase but the runoff decreases Figure 4. 3.3.2 Impact of land cover changes on water yield condition in CitanduyHulu subwatershed The impact of land cover changes based on 30 forest land cover scenario shows that discharge tends to decline contrary to evapotranspiration Figure 5. Water yield which derives from runoff contribution tends to decrease, while lateral flow and base-flow tends to stable. Compare to the 70 agroforestry land cover scenario, runoff and base-flow have the significant changes. Both of scenarios affect to the discharge reduction. Runoff contribution on water yield with 30 forest land cover tends to greater than 70 agroforestry land cover. Whereas base-flow contribution on water yields with 70 agroforestry land cover tends to greater than 30 forest land cover. Bogor, 21-22 October 2015 659 Figure 3: Changes trend for each of water yield component in Citanduy Hulu sub watershed Figure 4: Changes trend for each of flow on the discharge in Citanduy Hulu sub-watershed Bogor, 21-22 October 2015 660 Figure 5: Changes trend for each of water yield component in Citanduy Hulu sub-watershed affected by 30 forest land cover and 70 agroforestry land cover Figure 6: Changes trend for each of flow on the discharge in Citanduy Hulusub-watershed affected by 30 forest land cover and 70 agroforestry land cover Bogor, 21-22 October 2015 661 Both of scenarios indicates when the discharge and rainfall increase, the lateral flow and baseflow also increase but the runoff decreases Figure 6. When the discharge and rainfall increase, forest land cover with 30 coverage produces runoff higher than 70 agroforestry land cover.Whereas 30 forest land cover produces baseflow lower than 70 agroforestry land cover. While lateral flow generated by the two scenarios do not show the significant changes.

4. CONCLUSION