Examining the Impacts of Land-Use Change on Hydrologic Resources

The research community over the past several years has put a great effort into studying the potential impacts of a changing climate. But the issues that face the world today encompass greater change than just that of climate. For instance, there are changes due to population dynamics (such as migration), economics, and the way that land is used. Water resources are affected specifically by changes in climate and land use. A water balance developed for the purpose of examining climate change was extended to allow analysis of impacts from land-use change. In addition, it was modified so that a watershed could be modeled by multiple smaller units within the basin. Two methodologies were applied to break the basin into smaller parts: first, hydrologic boundaries of major tributaries were used, and second, a delineation based on five classes of land-use type, which included tundra, forest, rangeland, agriculture, and urban land, was created. The model originally had three parameters which were calibrated statistically. A goal of this project was to take a step towards making these parameters physically-based in the watershed, thereby avoiding the need for statistical calibration which might allow parameters to mask interconnections in the hydrologic process. The parameter which represents maximum soil moisture capacity was therefore set based on land-use type. The South Platte Basin upstream of the town of Masters, Colorado was chosen as a case study basin. The study included eight sub-basins delineated by hydrologic boundaries and the five land classes mentioned previously. A climate change sensitivity analysis was performed and a hypothetical land-use scenario was analyzed. This hypothetical scenario increased the percentage of urban land and removed all agriculture. In addition, some rangeland was converted to forested land. These tests were examined individually and in a combined scenario. Results found that the land-use scenario estimated greater runoff and acted to mitigate negative effects and enhance positive impacts of climate change. The magnitude of the impact of land-use change was found to be of the same order as that of climate change, and it therefore further warrants further research into possible effects of such changes. The study clearly demonstrated the sensitivity of model results to inclusion of land-use change, and the need for further development of the hydrological model for the Yellow River basin in North China, a water-critical region of the LUC project study area.