Land Use and Climate Change Impact Assessment of Hydrological Characteristics Of Addalam Watershed Using Soil And Water Assessment Tool (SWAT)

Abstract

Assessing the future environmental impact of climate change and land use change as it greatly affects the hydrologic processes and physical condition of the watershed is important as a mitigation and adaptation strategies to minimize risks and vulnerability of the watershed.

Prediction of the possible outcome of rainfall change in 2050 to the watershed was one important index that SWAT model has generated. The measures for the goodness-of-fit of model predictions used during the calibration and validation periods were the Coefficient of determination (R2) and the Nash Sutcliffe Simulation Efficiency (NSE), these numerical model performance measures the fraction of the variation in the measured data that is replicated in the simulated result of the model which was the basis of the acceptability of the model simulated values.

The SWAT model was parameterized and calibrated to simulate the hydrologic responses of the Addalam watershed to land use and climate changes using the A1B medium range climate scenario of PAGASA using the PRECIS (Providing Regional Climates for Impacts Studies, pronounced pray-sea) model. The A1B medium range climate scenario of PAGASA was used to capture the future impact of climate change and land use change. The seasonal temperature change and rainfall change in 2050 revealed a significant change in the annual water balance parameters of the watershed.

Application of the model on analysis of integrated climate and land use changes indicated the positive impact of scenario 3 (reforestation) reveals the reduction of surface runoff and sediment yield in 2050-time frame as compared to scenario 1 which represents 2050 climate and rainfall increase and scenario 2 (50% transformation of agricultural land to urbanization) of about 4.47% converting 50% of Agricultural land and 100% of grassland to forest area.

It was concluded that the increased surface runoff and sediment yield in 2050 time slices could trigger more landslide and erosion and flooding in low lying areas. And it will be recommended that adaptation strategies should be formulated to address these issues and associated impacts affecting development in the area. An advance planting dates of crops during dry months is one way of addressing farmers on the expected rainfall reducing the impact of water scarcity and hazards.