involves a pixel to pixel comparison of different land-cover data representing two different time periods in a GIS environment (Long et al. 2007; Tsegaye et al. 2010).
3.2 SWAT Model
SWAT is a hydrologic modeling tool designed to evaluate surface runoff, soil water content, groundwater discharge, and evapotranspiration. SWAT has proven to be an effective tool for assessing water resources and land-cover changes over a wide range of scales (Zhang et al. 2010). Table 1 lists the eleven parameters used in the calibration process from the SWAT models. They were selected based on the list in SWAT calibration tool and extensive literature review (Zhang et al. 2009; Mosbahi et al. 2014). For this study, three SWAT models were built with three simulation periods; period 1 (LULC with weather data from 1970 - 1989), period 2 (NLCD1992 with weather data from 1990 - 1999), and period 3 (NLCD2001 with weather data from 2000 - 2009). We employed three different land-cover data representing each period to simulate the most realistic hydrological model because land-cover data play an important factor in water resources response (Table 2). The SWAT models were calibrated and validated for the first and second half of each period, respectively. We simulated three SWAT models independently