Modeling land use change impacts on hydrology and the use of landscape metrics as tools for watershed management: The case of an ungauged catchment in the Philippines

The impacts of land use/land cover (LULC) change and the relationship between landscape pattern and hydrologic processes in the ungauged Calumpang watershed, Batangas, Philippines were studied. LULC change from 2003 to 2008 included an increase in built-up areas (69%) and a reduction of mixed vegetation including riparian vegetation (-10%), which have significant effects on hydrology. Using the Soil and Water Assessment Tool (SWAT), significant increases in surface runoff (5%) and sediment yield (6%) and a reduction in baseflow (-11%) were shown. Spatial and temporal variations of the impacts were observed: degraded sub-basins experienced increased streamflow (up to 31%) during stormy months and reduced baseflow (up to -26%) during dry months. In contrast, improved sub-basins decreased stormflow (up to -4%), and increased baseflow (up to 5%) during dry months. Nine landscape metrics known to affect hydrology were quantified using Fragstats and were correlated with surface runoff, basefiow and sediment yield using partial least square (PLS) regression. The results indicated that increasing patch density and largest patch index of agricultural and forested landscapes, respectively, leads to a decrease in surface runoff and sediment yield while increasing baseflow. In contrast, increasing cohesion and aggregation index of agricultural and forested landscapes, respectively, results to an increase in surface runoff and sediment yield as baseflow decreases. Although more observed data is needed for validation, the relationship model produced in this study can be applied to new data or used for scenario analysis. When coupled with economic, social and political assessments, the model serves as a useful tool in formulating comprehensive watershed management and land use policies.