A Quantitative Framework for Assessing the Effects of Climate and Land-use Change on Streamflow.

TOUMA, DANIELLE ELIE. A Quantitative Framework for Assessing the Effects of Climate and Land-use Change on Streamflow. (Under the direction of Dr. Ranji Ranjithan, Dr. E. Downey Brill and Dr. Sankar Arumugam.) The objective of this research was to develop and test a framework that can be used to assess the effects of climate and land-use change on the stream ecology in a basin. The current method of analyzing extreme events of streamflow is insufficient in non-stationary environments. Although tools and models are available for this assessment, no systematic approach is established. The proposed framework outlines and integrates the key steps and necessary procedures to assess the changes in streamflows. Precipitation and temperature data from four General Circulation Models (GCMs) and land cover data from a land-use model were coupled with a hydrologic model to simulate daily flows. The GCM monthly precipitation and temperature data were preprocessed using a downscaling method to achieve data on a refined spatial scale and a k-Nearest Neighbor algorithm was used to temporally disaggregate the data to a daily scale. The housing density data from the EPA Integrated Climate and Land-use Scenarios (ICLUS HD) were reclassified to be compatible with the USGS National Land Cover Database. The Soil and Water Assessment Tool (SWAT) was used to process the land-use and climate data in the basin. The flow values were used to estimate several Indicators of Hydrologic Alteration (IHA) which were then assessed for the amount of changes using the Range of Variability Approach (RVA). The hydrologic alterations are evaluated based on flows in a pre-development period and post-development period. To assess the changes under reduced scenario uncertainties and realistic planning time frames, the post-development period flows were scenario simulated for 2011-2040, while the pre-development period flows were simulated using the observed conditions between 1981-2010. The North East Cape Fear River basin was used to illustrate the framework. The SWAT model was calibrated to an R 2 of 0.69 for the daily streamflow. The A2 and B1 scenarios from the Fourth Assessment Report from the Intergovernmental Panel for Climate Change were used in the framework to drive the climate and land-use changes in the postdevelopment period. The basin is expected to experience 3.4 – 10.8% increase in mean precipitation, 0.35 – 1.10 °C increase in mean temperature based on four different types of GCMs. Urban development is expected to increase by 14 – 17% between the predevelopment period and the post-development period which is representative of the A2 and B1 scenarios. The mean flows increased by 1.6-19.6% under climate change simulations but do not change more that 0.01% under land-use change simulations. Changes in mean flows and some mean monthly flows under climate change conditions were statistically significant to a 95% level for all GCMs and both the A2 and B1 scenarios but were not significant under land-use change conditions. The combination of both land-use and climate change provided the same alterations as climate change alone. The IHA parameters showed alterations in the annual minimum and maximum daily means and mean monthly flows for all GCMs under climate change for both scenarios, even when the mean changes were not shown to be statistically significant. Flows simulated under land-use change, however, showed no hydrologic alteration. Overall, the climate change for the A2 scenario showed the most alteration in the basin. There was a wide variation among the simulations under the different GCM data sets that leads to uncertainty in the flows. The framework was found to streamline the tools and methods used in modeling the streamflow in the basin under climate and landuse change conditions and enable systematic assessments of their affects on ecological flow alterations. Further investigation into the uncertainty in the flows is needed, while other preprocessing tools such as multi-model combinations can be integrated into the framework to potentially improve it. A Quantitative Framework for Assessing the Effects of Climate and Land-use Change on Streamflow by Danielle Elie Touma A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science