Yiping (Rocky) Wu

　　Department of Earth & Environmental Science Xi’an Jiaotong University, China

　　Increased atmospheric CO₂ concentration, climate change, and land-use change may significantly impact the hydrological processes of a watershed system. Quantifying and understanding hydrological responses to these environmental changes is, therefore, critical for formulating adaptive strategies for sustainable management of water resources. In this study, we modified the Soil and Water Assessment Tool (SWAT) model to represent more mechanistic vegetation type specific responses of stomatal conductance reduction and leaf area increase to elevated CO₂. Then we used the new model to investigate the historical impacts of CO₂ enrichment and predict the impacts of a shifting climate by the end of the 21^st Century derived by four General Circulation Models (GCMs). On the other hand, perennial dedicated energy crops are regarded to be the second-generation or advanced biofuel feedstocks (cellulosic feedstocks) to meet the rising demand for energy due to its net carbon emission. Therefore, we also evaluated the potential consequences of biofuel-induced land-use changes (e.g., converting grassland to bioenergy crops) using our modified SWAT which can facilitate the implementation of land-use change scenarios. For assessing the effects of climate and land-use changes in the Midwestern U.S. which is sensitive to human activities, we selected the representative moderately-humid Upper Mississippi River Basin (UMRB) and semi-arid James River Basin (JRB) as the case study areas. The results indicated that about 1–4% of the streamflow in the UMRB during 1986 through 2008 could be attributed to the rising CO₂ concentration. Simulations with land use change scenarios in the JRB could help us spatially classify the grasslands in terms of biomass productivity and nitrogen loads, and we further derived the relationship of biomass production targets and the resulting nitrogen loads against switchgrass planting acreages. Besides, we derived a pareto optimal frontier suggesting economically efficient (planting acreage) and environmentally friendly (water quality) planting locations and acreages. Overall, the above climate and land-use change studies would be a valuable guide for decision makers when taking measures to cope with climate change and cultivating bioenergy crops in the Midwestern U.S.