Assessment of land-use impact on streamflow via a grid-based modelling approach including paddy fields

To investigate the hydrologic impacts of land-use changes on streamflow for an urbanizing watershed with paddy fields, a grid-based daily hydrologic model was adopted. The model was calibrated with two years (2000-2001) of observed streamflow data and validated using 5 months (2001) of measured soil moisture data and 1 year (2002) of observed streamflow data. After the model was tested, it was run to estimate impacts of urbanization on each hydrologic component with the land-use data sets for 1986, 1994, and 2002 generated from Landsat TM satellite images. Total runoff increased from 41.4% (1986) to 44-9% (2002) for a 5.4% increase in urban area, implying that direct runoff increase exceeded baseflow decrease. Urbanization affected the proportions of direct runoff for each land-use category more than the change in total runoff and the ratio of direct runoff to total runoff. The change proportions in direct runoff for urban areas, paddy fields, and forest were 14.3%, -9.8% and -6.7% respectively for a 5.4% increase, 4.6% decrease and 3.4% decrease in each land-use area respectively. The results indicate that paddy fields play an important role in runoff regulation, and the evaluation method can assist regional policy makers in developing land management strategies that minimize hydrologic impacts on streamflow. Copyright (c) 2005 John Wiley & Sons, Ltd.