INTEGRATED USE OF REMOTE SENSING, GIS AND SWAT MODEL TO EXPLORE CLIMATE CHANGE EFFECTS ON RIVER DISCHARGE IN THE CAGAYAN RIVER BASIN AND LAND COVER-BASED ADAPTATION MEASURES

摘要

Land cover-based adaptation measures have already been adopted by many concerned institutions in response to the posing ill-effects of climate change. Such scheme is usually achieved using an integration of watershed models, Remote Sensing (RS) and Geographic Information System (GIS). In this study, GIS provided the platform for the ArcSWAT interface of the Soil and Water Assessment Tool (SWAT) model. The model was used to assess the effect of climate change on river discharges from the Cagayan River Basin-the largest river basin in the Philippines-with inputs including land use/land cover maps from RS data (Landsat TM and ETM+ images), Shuttle Radar Topography Mission Digital Elevation Model (SRTM-DEM), soil map and hydrologic data. Automatic watershed delineation was done via the ArcSWAT interface using the input DEM while subbasins and finer subdivisions in the basin called the hydrologic response units (HRU) are defined by setting threshold limits for land use/land cover, soil type and slope class. Values of the Nash-Sutcliffe Efficiency (NSE)＞0.6 and coefficient of determination (R~2)＞0.7 for both model calibration and validation of mean daily river discharges showed that SWAT can realistically model flow dynamics in the study area. Reruns of the calibrated model have demonstrated how changes in climatic parameters, such as rainfall and temperature, can significantly affect river discharge. Specifically, it has been shown that discharge will increase for A1B climate change scenario in years 2020 and 2050 and in general, the proposed land cover distribution scheme has become a control mechanism by successfully reducing river discharge. The study has demonstrated how the integration of RS, GIS and SWAT model can be a powerful tool in watershed management and protection.