Water balance change under climate and landuse/landcover variability in the North Carolina Piedmont.

摘要

Fresh water availability is an important concern for human society as well as ecosystems. In this dissertation, water resources trends in the North Carolina Piedmont were analyzed to understand historical trends and provide potential future scenarios in response to different climate and landuse/landcover (LULC) dynamics. North Carolina Piedmont has experienced a large scale LULC conversion from farmland to naturally grown forest, followed by recent urbanization, in the last century. Simulation with the Soil and Water Assessment Tool (SWAT) indicates that forest re-growth mitigated the impact of increased precipitation on stream discharge in areas that reforested from abandoned agricultural fields due to increasing water consumption. For projected climate conditions, nested global and regional circulation model results from the North American Regional Climate Change Assessment Program (NARCCAP) were evaluated for bias relative to current measurements in North Carolina. For historical NARCCAP output (1971-2000), precipitation shows seasonal bias pattern and, there is a general trend of NARCCAP temperature cold bias. After applying bias correction methods, NARCCAP climate simulation outputs have significant reduction of seasonal biases in precipitation temperature except for a few extreme events. For future projections of monthly runoff production, a set of scenarios are used for SWAT simulations with increasing carbon dioxide (CO2), projected climate and LULC. Under future climate conditions evapotranspiration (ET) is projected to increase in winter and spring while annual water yield (WY) would show various changing patterns, with greater dependence on projected CO2 and precipitation. When only future climate scenario was included, the highest WY was produced by combining increasing CO2 and future precipitation while future temperature alone produced the lowest WY. When projected LULC is applied, future urban growth may cause decreased ET and increased WY because of the imperviousness increment. However, interaction between climate and LULC change can mitigate these effects. Most of the simulation scenarios projected WY similar or slightly lower than current WY on an annual basis due to the offsetting effects of increasing temperature and urbanization. Therefore, it is necessary to incorporate interactions of all factors, CO2, climate and LULC change, to simulate future water availability in the North Carolina Piedmont.