Description

Summary: The implementation of the Environmental Impact (SWAT Modeling) component of this SANREM CRSP project in year 3 was highlighted by further work on SWAT model development in Indonesia, Philippines and Vietnam. In all three countries, additional input data have been collected over the past year for SWAT modeling purposes. Data Elevation Models (DEMs), land use maps and soil maps have also been prepared in all three countries. In the Philippines, SWAT model has been developed for assessing the hydrologic effects of land use changes. Other SWAT models for small upland watersheds have also been developed and are being refined. In Indonesia and Vietnam, SWAT model development work is underway.

Initial SWAT simulation results in the Philippines showed that conversion of forest to agricultural lands causes serious erosion and sediment yield in the area. Agricultural lands planted with corn, potato and tomato which comprise about 22.38% of the test watershed area resulted to an average annual sediment yield of 110.1 t/ha with the areas planted with potato producing the largest sediment yield of 205 t/ha. Forest and pasture and/or grassland yielded a sediment yield of 0.7 t/ha and 2.15 t/ha, respectively. On the average, simulation results showed an annual sediment yield of 12.86 t/ha for the whole area. SWAT models were also developed for Kiluya and Kalaignon subwatersheds of Alanib river. Using hydrologic data, the models performed satisfactorily during model calibration with an explained variance ranging from 0.86 to 0.89. Primary hydrologic and climatological data collection has also commenced in the test watersheds, in partnership with Dr. Conrad Heatwole of Virginia Tech, to generate adequate basis for model calibration and validation.

In Indonesia and Vietnam, SWAT model simulations are yet to be performed. Significant findings on hydrologic effects of land use particularly VAF systems based on SWAT model simulation are expected to be generated in the ensuing year of project implementation.

Although more substantive SWAT modeling work will be done in year 4 of project implementation, results of SWAT modeling work generated so far have far-reaching implications on sustainable natural resources management in Southeast Asian watersheds. SWAT modeling results in this region will be presented at the SWAT-SEA Conference to be held in Chiang Mai, Thailand in January 2009.