THE LONG-TERM HYDROLOGICAL IMPACT ASSESSMENT OF LAND USE AND LAND COVER CHANGES USING L-THIA MODEL IN THE QINHUAI RIVER WATERSHED OF JIANGSU PROVINCE, CHINA

This study examined the effects of land use and land cover changes due to urbanization on the annual direct runoff of the Qinhuai River Watershed in Jiangsu Province, China. Landsat Thematic Mapper (TM) images from 1988, 1994, 2006, Enhanced Thematic Mapper Plus (ETM+) images from 2001 and 2003, and China-Brazil Earth Resources Satellite (CBERS) image from 2009 were used to obtain historical land use and land cover maps. These maps revealed that the watershed experienced conversion of approximately 16% non-urban area to urban area between 1988 and 2009. The Long-Term Hydrological Impact Assessment (L-THIA) model was used to calculate direct runoff generation. The model was calibrated and validated using observed daily stream flow data collected at the outlets of the watershed, and then repeatedly run with different urbanization scenarios to investigate the hydrological response to land use changes. The simulation results of L-THIA model for the various urbanization scenarios indicate that when the impervious surface area changed from 3.4% of 1988 scenario to 20.5% of 2009 scenario, the average annual direct runoff depth would increase from 355 mm to 496 mm. The results also indicate that the annual direct runoff depth is highly correlated with the percentage of impervious surface area. When impervious surface area is less than 9.0%, the annual direct runoff depth will increase linearly with impervious surface area (R 2 =0.97); however, when impervious surface area is greater than 9.0%, the annual direct runoff depth will also increase linearly with impervious surface area (R 2 = 1.00) but at much lower rate.