Modelling the effects of adopting agroforestry on basin scale surface runoff and sediment yield in the Philippines.
Modelling the effects of adopting agroforestry on basin scale surface runoff and sediment yield in the Philippines.wca2014-1576 David Wilson 1,*Rodel Lasco 1 1World Agroforestry Center, Los Baños, Philippines
The Carood watershed incorporates a heavily degraded, mosaic landscape covering 21, 407 hectares in the province of Bohol, Philippines. The area is home to around 60,000 people whose principal livelihood activities of subsistence agriculture – particularly rice and maize production – as well as livestock management and aquaculture, are closely bound to the ecosystem services provided by the watershed. The degraded nature of the watershed, which has been largely deforested and replaced with extensive agricultural and grasslands over the last half century, has disrupted the evenness of river flow resulting in alternate flooding and drought episodes, an accelerated level of soil erosion as well as downstream sedimentation. The degradation of the landscape has impacted the economic activities of local communities and alternative land-use practices which continue to offer livelihood benefits are required to tackle the associated environmental problems. However, reported problems remain largely anecdotal with limited available hydrological data. This study therefore, uses Soil and Water Assessment Tool (SWAT) to simulate the effects on watershed hydrology of different land use practices under two scenarios: current land-use practices and improved land management using agroforestry in strategic locations. Using a combination of observed climatic and soil data, land-cover and geomorphological data derived from high-resolution satellite imagery the results reveal the effects of different land-use practices on the quality (sediment load), quantity (surface runoff) and seasonal availability (evenness of flow) of water in the Carood watershed. The simulations demonstrate that the adoption of agroforestry in strategic locations represents an effective land-use option to address the reported water quality and quantity issues. In particular, the use of carefully located or restored riparian buffers in addition to contour planting in grasslands appear to be the most effective techniques to reduce sediment transfer to the watershed river network.