CLIMATE AND HYDROLOGIC CHANGE ASSESSMENT FOR GEORGIA F. Zhang and A. Georgakakos AUTHORS: School of Civil and Environmental Engineering, Georgia Institute of Technology, 790 Atlantic Dr. Atlanta, GA 30332. REFERENCE: Proceedings of the 2011 Georgia Water Resources Conference, held April 11-13, 2011, at the University of Georgia. Abstract. This article describes a climate change and hydrological impact assessment for several basins in Georgia. First, a new statistical technique, Joint Variable Spatial Downscaling (JVSD), is developed to produce high resolution gridded hydrological datasets for the Southeast US from 13 different Global Circulation Models (GCMs). A lumped conceptual watershed model (Geor- gakakos et al., 2010) is then employed to characterize the hydrologic responses under the historical climate and the future climate scenarios. The historical (baseline) assess- ment is based on climatic data for the period 1901 through 2009. It consists of running the hydrological models un- der historical climatic forcing (of precipitation and tem- perature) for the 109 year period from 1901 to 2009 (in monthly steps). The future assessment consists of running the Georgia watershed models under all A1B and A2 cli- mate scenarios for the period from 2000 through 2099 (100 years) in monthly time steps. For the baseline sce- narios and each of the 26 future climate scenarios (i.e., 13 A1B scenarios and 13 A2 scenarios), this study assesses the changes of both climate variables (i.e., precipitation and temperature) and hydrologic variables (i.e., soil mois- ture, evapotranspiration, and runoff) for each watershed. The results show that: (1) the 26 IPCC future climate sce- narios (2000-2099) do not indicate any long term change in average precipitation; (2) the precipitation distribution is expected to “stretch” becoming wetter and drier than that of the historical climate; (3) temperature and potential evapotranspiration (PET) show consistently increasing historical and future trends; (4) soil moisture storage ex- hibits a declining trend historically and for future climates; and (5) watershed runoff, and thus river flow, exhibits a similar historical decline across all Georgia watersheds. INTRODUCTION Current water resources planning and management prac- tices in the Southeast US may be vulnerable to the poten- tial impacts of future climate changes on both water quan- tity and water quality. These are largely due to the hydro- logical stationarity assumption among policy and decision makers who are often unconcerned about climate and en- vironmental changes over the coming decades. An integra- tive approach to assessing climate change impacts on wa- ter resources by following a well-defined assessment framework is crucial to regional water resources managers (Georgakakos et al., 1998). Generate consistent climate forcing sequences, i.e., rainfall, temperature etc. River/ Reservoir Planning & Management Simulate soil moisture, evapotranspiration, runoff, etc. GCM Scenarios Bias Correction Downscaling Assess Impacts on water uses & users. Watershed Hydrology Reg. Reservoir Runoff Reservoir Control Point Local Inflow Withdrawal Legend Lake Lanier 105MW Sumatra Norcross Blountstown Chattahoochee 36 MW Woodruff Bainbridge Newton Albany Montezuma Griffin Andrews W. George Columbus N. Highlands Oliver Goat Rock Bartletts Ferry West Point 82 MW Whitesburg Atlanta 16.8 MW Morgan Falls 168 MW Engage Stakeholders & Support Planning & Managmnt Processes. OBS Cells (~12 x 12 km2): • Monthly & Daily • 1950-1999 (50 Years); • Temperature, Precipitation GCM Cells (~250 x 250 km2): • Monthly & Few Daily • A1B: 2001-2100; (100 Years) • A2: 2001-2100; (100 Years) Figure 1. Integrated Modeling Framework The aim of this study is to develop an integrated climate change assessment framework and to generate reliable data and information to support the on-going re- gional water resources planning and management efforts in Georgia and the southeast US. Figure 1 illustrates the integrated modeling framework comprising three main components: (1) processing of general circulation model (GCM) scenarios for bias correction and downscaling (climate component); (2) developing physically based conceptual models for all ACF sub-watersheds (hydrology component); and (3) representing all ACF regulation in- frastructure and water uses within an adaptive river and reservoir regulation and assessment model (water re- sources component). CLIMATE CHANGE SCENARIOS Many researchers have demonstrated the physical science basis, impact, adaptation and vulnerability of our changing climate and environment. The climate change issues have been addressed in a couple of literatures for the impact on water resources (Lettenmaier and Rind, 1992; Stamm et al., 1994; Conway, 1998; Wood et al., 2004;). Among these studies, as an important tool for qualitative impact