Evaluation of Runoff Responses to Land Use Changes and Land Cover Changes in the Upper Huaihe River Basin, China

Runoff changes in response to land use and land cover changes in the Huaihe River were drastic in the last few decades and are poorly understood because results from those studies are often equivocal. Hitherto, the methodology to quantify the effects of land use and land cover changes on the runoff response has been mainly the paired catchment approach, which is a blackbox, and usually restricted to small headwater basins where a control can be established. A model-based change-detection approach is developed in this study as an alternative to paired catchment methods. This approach is particularly suited to evaluating effects of land use and land cover changes on the hydrologic response in large to mesoscale watersheds in which suitable control is not possible. The Xinanjiang model was used to evaluate the newly implemented approach in the Dapoling watershed (with an area of $1,640{\mathrm{km}}^2$) in the upper Huaihe river basin. Three schemes were used to examine changes in the data series: (1) Calibration for a period before (or after) changes and simulations of runoff that would have been observed without land use and land cover changes (reconstruction of runoff series); (2) comparison of calibrated parameter values for periods before and after the land use and land cover change; and (3) comparison of runoffs simulated with parameter sets calibrated for periods before and after the landcover change. The results show that, since 1976, the medium-coverage and high-coverage natural forest area has decreased, and the corresponding runoff has declined by nearly 25% from 1976 to 2005 attributable to the continuous expansion of tea gardens and human development. Model parameters, for example, the evapotranspiration coefficient KC, varied considerably from 0.64 to 0.94 attributable to the land use and land cover change within the watershed. This study demonstrates that the modeling approach may be a useful alternative to the paired watershed approach for examining land use and land cover changes and their impact on the runoff.