Person:

Georgakakos, Aristidis P.

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https://hdl.handle.net/1853/71284

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School of Civil and Environmental Engineering

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Now showing 1 - 10 of 29

Hydro-Climatic Trends in the Southeastern US

(Georgia Institute of Technology, 2013-04) Regan, Jeffrey ; Georgakakos, Aristidis P.

Indications of a climatic change on a global scale are increasingly calling into question what we know about and what to expect from our own local climates. A changing climate means the traditional method of using historical hydro-climatic conditions as expected conditions in water planning and management may be unwise. New methods for determining and characterizing expected local hydro-climatic conditions should consider an evaluation of how historical local hydro-climatic conditions have changed over time. In this sense, an evaluation of hydro-climatic trends in the Southeastern US has been developed using historical records from weather gages. Trends for monthly precipitation, maximum and minimum temperatures, evaporation, and stream flow have been developed for various historic time intervals during 1909 to 2009. The historic hydro-climatic trends have been plotted and mapped in a manner to easily show seasonal and regional shifts that have occurred in the past 50 and 100 years. These trends vary by season and location, and there are few trends that appear to be region-wide and no trends that appear year-round. In the past 100 years the annual temperature records region-wide indicate a cooling trend strongest during winter and fall and weakest during summer months. However 50-year trends indicate a warming trend in almost all months region-wide. The 100-year trends of precipitation indicate an increase in annual precipitation in most areas, however, a decrease during the driest summer months. The 50-year trends indicate a decrease in annual precipitation and increased evaporation in almost all regions. Identification and illustration of these trends is an important step in debunking the traditional notion that “what was, will be” and moving towards a non-stationary hydro-climatic approach to water planning and management.
Environmental Flow and Ecological Impacts of Alternative Regulation Scenarios for the ACF River Basin

(Georgia Institute of Technology, 2011-04) Kistenmacher, Martin ; Georgakakos, Aristidis P.

This article presents a study that evaluates the impact of several different alternative regulation scenarios on the environmental flows within the Apalachicola-Chattahoochee-Flint (ACF) river basin. A river basin model is used to simulate the flow of water through the basin under each regulation scenario. The resulting river flows are then analyzed to determine the effects of different regulation policies on environmental flows. A variety of water uses exist within the ACF basin. Water is withdrawn to support municipal, agricultural, and industrial uses, while hydropower can be generated at several locations throughout the river basin. There is also demand for water to be kept within the rivers for recreation and navigation. Additionally, environmental flow regimes represent in-stream uses of water that are designed to help sustain the natural ecosystem. The basin contains several large reservoirs that can be used to regulate the flow of water and help allocate it to different uses. Driven by long timeseries of historical inflow data, the ACF-DSS river basin model is used to simulate different regulation scenarios. For each scenario, the resulting output consists of timeseries of system variables such as withdrawals, hydropower production, reservoir elevations, and river flows. The impacts of a particular regulation scenario on the environmental flows and river ecology are determined by analyzing the river flows at several locations through the basin. Using the Indicators of Hydrologic Alterations (IHA) software (Nature Conservancy, 2009), a host of biologically relevant statistics is calculated. By comparing each scenario’s statistics to those resulting from the natural unimpaired river flows, the degree of hydrologic alteration caused by the specific regulation policy is determined. Additionally, the statistics from different scenarios are compared to each other to identify which regulation policies provide desirable flow regimes for ecosystem protection.
Climate Change Impacts on Georgia Agriculture and Irrigation Demand

(Georgia Institute of Technology, 2011-04) Braneon, Christian ; Georgakakos, Aristidis P.

The agriculture industry plays a huge role in Georgia’s economy, contributing billions of dollars annually. In addition, the state’s water resources are intrinsically tied to the agricultural sector since both surface water and groundwater are used by farmers to irrigate crops with groundwater accounting for over sixty percent of agricultural water demand. Although Georgia is typically considered to be a state with plentiful water resources due to average annual rainfall exceeding that of many other parts of the United States, the competing demands placed on water resources by the municipal, industrial, agricultural, and ecological sectors make water resources management and planning a significant challenge for stakeholders and policy makers. This is complicated further by the uncertainty surrounding agricultural water use due to a lack of observed data regarding agricultural water application rates and seasonal volumes. Furthermore, climate change has the potential to decrease the availability of water resources due to probable changes in rainfall distribution and increases in potential evapotranspiration demand. In this study, the Decision Support System for Agrotechnology Transfer (DSSAT) suite of crop models is utilized along with available daily weather data (precipitation, minimum and maximum temperature, and solar radiation) from the Georgia Environmental Monitoring Network (GAEMN), the National Climatic Data Center (NCDC), and the National Solar Radiation Database (NSRDB) to estimate historical irrigation volumes for farmers irrigating Georgia’s primary field crops (peanut, cotton, and maize). Historical crop yield and acreage data from the National Agricultural Statistics Service (NASS) is used to calibrate model parameters and determine locally acceptable plant water stress as a management parameter. The plant water stress parameter is used to mimic the farmers’ decision on when and how much to irrigate during the growing season. Climate change assessments are in progress using spatially and temporally downscaled weather data from selected general circulation models. Results are presented here showing estimated seasonal water demand for peanut production in Decatur County for the 2002-2008 time period. A comparison of simulated and NASS estimated yields is also presented. The model is able to represent historical yields well with simulated yield after calibration typically within two percent of NASS estimated yield. Irrigation volumes range from 34 to 359 mm, with the least water demand in 2008 and peak water demand in 2007. Future work will focus on developing probabilistic assessments of the relative changes in crop yield and water demand that are derived from climate change scenarios.
Climate and Hydrologic Change Assessment for Georgia

(Georgia Institute of Technology, 2011-04) Zhang, F. ; Georgakakos, Aristidis P.

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 (Georgakakos et al., 2010) is then employed to characterize the hydrologic responses under the historical climate and the future climate scenarios. The historical (baseline) assessment is based on climatic data for the period 1901 through 2009. It consists of running the hydrological models under historical climatic forcing (of precipitation and temperature) 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 climate scenarios for the period from 2000 through 2099 (100 years) in monthly time steps. For the baseline scenarios 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 moisture, evapotranspiration, and runoff) for each watershed. The results show that: (1) the 26 IPCC future climate scenarios (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 exhibits 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.
A Hydro-economic Model for Integrated Water Resources Assessment

(Georgia Institute of Technology, 2011-04) Frederic Kimaite ; Georgakakos, Aristidis P.

This article presents a detailed hydroeconomic modeling tool used to assess potential economic tradeoffs of alternative water resources management policies and development options under different climate scenarios. The tool leverages the strengths of detailed hydrological, water resources, and economic models to accurately represent the complex and multi-objective physical, management, and socio-economic decision processes in a basin. On the supply side, detailed hydrological and water resources assessment models (including operational Turbine Load Dispatching Models, Short and Long Range Reservoir Management and River Simulation Models, Inflow Forecasting Models, Climate Change Assessment Models, and Scenario/Policy Assessment Models) are used to simulate the spatial and temporal water availability in different parts of the basin subject to inflow variability and potential climate change, water use withdrawals and returns, and system constraints imposed by different management policies. On the demand side, detailed economic models based on inductive and deductive water valuation techniques are used to derive marginal economic benefit functions for different water use sectors. The tool is applied to the Apalachicola-Chattahoochee- Flint (ACF) basin in the Southeast US (Figure 1) to assess the economic tradeoffs of two alternative water resources management policies under current and potential future climate conditions. The alternative management policies are the Interim Operations Plan (IOP) used by the US Army Corps of Engineers (US ACE) and a new operational plan proposed by Georgakakos, 2010 (GTIOP). Preliminary results (Figure 2) show that (a) GT-IOP clearly outperforms the current ACF water resources management policy under both historical and future climates; and (b) the ACF basin is likely to experience significant water related economic losses due to potential future climate change unless appropriate mitigation measures are implemented.
Seasonal Rainfall Prediction for the Southeast U.S. Using Sea Surface Temperature Information

(Georgia Institute of Technology, 2011-04) Chen, Chia-Jeng ; Georgakakos, Aristidis P.

This article presents a novel method able to identify and use the most relevant sea surface temperature (SST) information for seasonal rainfall prediction in the Southeast United States (SE US). The method searches for oceanic dipole areas with strong teleconnection relationships with rainfall, and generates seasonal forecasts based on a Bayesian forecasting scheme. The dipoles comprise oceanic areas of various sizes and geographic location, with the difference of the average SST over the poles being the predictor information. Dipole generation is based on teleconnection strength evaluation by the Gerrity Skill Score (GSS). In this application, seasonal rainfall series in the SE US is adopted as the predictand variable. Results show that the strongest predictability exists in winter (December – February). Even at lead times of 3 – 6 months, ensemble forecasts explain more than 50% of the observed rainfall variation. Zonal dipoles in North Atlantic near the Tropic of Cancer, dipoles between North Pacific and Northeast Atlantic, and ENSO-like dipoles are the most statistically significant patterns influencing winter SE US rainfall. Temporal and spatial persistence of SST are identified as oceanic patterns driving corresponding atmospheric circulation modes and affecting rainfall. Skill in other seasons are moderate compared to winter, however useful predictabilities appear in different lead times. On-going work focuses on assessing the value of the forecasts for agriculture and water resources management. Three rainfall stations at Buford dam, West Point Dam, and Montezuma as shown in Figure 1 are used for generating seasonal rainfall series. The monthly average rainfall climatology is also shown indicating that winter rainfall is significant for the ACF water resources. Figure 2 presents ensemble forecast results of winter rainfall with 6 months lead time compared with observations. In the model calibration period, from 1951 to 2000, more than 80% of observations fall in the reliability band. The remaining 9 years, from 2001 to 2009, are used to test the skill of model forecasts. The figure shows that 8 of the 9 seasons fall within the forecast band, indicating considerable skill. Overall the root mean square error (RMSE) and the correlation coefficient (CORREL), derived between the observation series and the average forecasting trace, are 0.021 (m) and 0.730 respectively. These values indicate that the model compares favorably with other existing methods.
A New Hydrologic Routing Model with Applications for Georgia Rivers

(Georgia Institute of Technology, 2011-04) Kim, Dong Ha ; Georgakakos, Aristidis P.

In this paper, a new hydrologic river routing model is developed to identify storage-outflow relationships for different reaches of a river. The model is then incorporated into a Bayesian forecasting framework (BFF) to generate ensemble forecasts of river flows that incorporate hydrologic and model uncertainties. The routing model assumes that a river reach can be viewed as a cascade of conceptual reservoirs, each of which receives water from the upstream and releases water to the downstream according to a release rule. Additionally, these release rules are assumed to follow monotonically increasing storage-outflow relationships. Without any assumption on the mathematical structures of the rules, a Linear Quadratic Regulator (LQR) is used to identify the storage-outflow relationships. The routing model was tested on the Equatorial Lakes in East Africa because this system is a series of cascading reservoirs and because actual observations of the storageoutflow relationships are readily available. Given the initial storage of each lake, the model was able to find storage-outflow relationships that closely approximate the observed data, as depicted in Figure 1.. The storage-outflow relationships were then used to generate ensemble forecasts of river flows. Under this forecasting scheme, a historical analog method is used to select an ensemble of system inflows. Each inflow trace is then simulated with the previously estimated storageoutflow relationships to generate ensembles of river flows. In order to improve forecast performance, a Bayesian forecasting framework (BFF) was developed and used to generate updated river flow ensembles. The distributions of the river flow forecasts at the outlet of the lake system before and after the application of the BFF are shown in Figure 2. It can be seen that the variances of the BFF distributions (blue-colored box plots) are smaller than those of the pre-BFF distributions (gray-colored box plots), while the actual river flows that materialized (red dots) still fall within the forecasted ranges. The BFF derived forecasts therefore provide more concise forecasts without significant loss of reliability. The new routing model will be tested under various flow and terrain conditions for various rivers in Georgia. Comparisons with existing methods, such as Muskingum, Muskingum-Cunge, method of characteristics, and explicit/implicit routing schemes will be carried out to test model accuracy and efficiency.
ACF River Basin: Climate and Demand Change Impacts and Mitigation Measures

(Georgia Institute of Technology, 2011-04) Yao, Huaming ; Georgakakos, Aristidis P.

This article presents the potential impacts of climate change on the Apalachicola -Chattahoochee- Flint (ACF) river basin (Figure 1) in the southeast US. The long term future basin inflow sequences corresponding to A1B and A2 climate change scenarios were used to drive a water resources model that incorporates the river network, all storage projects and hydroelectric facilities, water withdrawals and returns, instream flow requirements, and management procedures. The assessment criteria of impacts include reliability of water supply for municipal, industrial, and agricultural users with current demand level (year 2007) and future projection (year 2050); lake levels; environmental and ecological flow requirements; and hydropower generation. Results indicate that, under the climate change scenarios and with the current management procedures, the system will experience severe adverse water resources impacts such as extended reservoir drawdowns (Figure 2), water supply deficits (Figure 3), and frequent violations of instream flow requirements. Adaptive management procedures and modified operation rules are proposed and tested to mitigate the impacts of climate changes. The results indicate that such measures can significantly reduce adverse climate and demand change impacts (Figure 4 and Figure 5), but they need to be institutionalized as part of state and federal agency policies.
Water and Conflict

(Georgia Institute of Technology, 2011-03-15) Bethea, Sally ; Cozzens, Susan E. ; Georgakakos, Aristidis P. ; Deutsch Lynch, Barbara ; Stiftel, Bruce
Georgia Water Resources Institute annual technical report FY 2010

(Georgia Institute of Technology, 2010-06-30) Georgakakos, Aristidis P.