Quantification of Stochastic Crop-Water Production Functions and Net Profit-Water Functions for Agriculture on the Edwards Aquifer

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1 Quantification of Stochastic Crop-Water Production Functions and Net Profit-Water Functions for Agriculture on the Edwards Aquifer Graduate Student Researcher: Ju Young Lee, Texas A&M University, Dept. of Civil Engineering, 3136 TAMU, Graduate Faculty Advisor: Dr. Kelly Brumbelow, Texas A&M Universit y, Dept. of Civil Engineering, 3136 TAMU, (979) Project Duration: March 2003 through February Problem Statement: The Edwards Aquifer is a site of extreme water resource demands for environmental, agricultural, and urban needs. As one part of its aquifer management policies, the Edwards Aquifer Authority (EAA) has imposed a cap on agricultural irrigators of 2 feet of irrigation per calendar year; of that amount, 1 foot can be sold on an open market. This policy is only a few years old, and experience with it is very limited from both the farm profitability and water resources management perspectives. Research is needed to assess how the EAA s 2 foot rule may affect long-term agricultural and water resources systems in the region. Nature, Scope, and Objectives of the Research: The Edwards Aquifer of central Texas (Figure 1) is an extraordinary water resource that is now the site of intense competition for water among urban, agricultural, and environmental interests. Due to the presence of endangered and threatened species in the San Marcos and Comal Springs fed by the aquifer, water use from the aquifer is carefully controlled by the Edwards Aquifer Authority (EAA) with an eye towards preservation of aquifer levels and outflows at the springs. One recent policy implemented by the EAA is to limit agricultural irrigators pumping from the aquifer to 2 acre-feet of water per cultivated area of land in each calendar year. This rule is significant in areas that may have as much as 0.5 inches of potential evapotranspiration on some summer days. Of the 2 feet of water allocated to each irrigator, up to 1 foot may be sold on an open market, and buyers from urban areas as well as speculators have emerged in to that market. The Winter Garden agricultural region of Kinney, Medina, and Uvalde Counties enjoys a mild winter climate which allows for production of high value crops well-timed for the consumer market. These factors sum up to produce a very complicated farm profitability calculus. Moreover, as monitoring of actual well pumping for irrigation has only been recently established, the true picture of agricultural water use for the full range of climatic conditions is only vaguely known. This project will accomplish two primary objectives oriented towards improved understanding of agricultural water use and farm profitability in this important region. First, this project will quantify the relationship of crop yield to seasonal irrigation (the crop-water production function or CWPF) for agricultural sites on the Edwards Aquifer for the fullest climatic record possible. Brumbelow and Georgakakos (2002a and 2002b)

2 have demonstrated the use of advanced optimzation techniques along with physiological ly based models of crop growth and development to determine CWPF s. By determining the CWPF s for a crop and site for multiple years of historical meteorology, the stochastic nature of the yield- irrigation relationship can be determined and expressed as a CWPF- Probability Distribution (CWPF-PD), and example of which is shown in Figure 2. The availability of accurate crop models for crops such as sorghum, corn, and cotton (e.g., Tsuji et al. 1998, etc.) will allow for appropriate analysis for several important regional crops. Some important crops (such as spinach) that are not included in that class of models will be analyzed using reference evapotranspiration and crop coefficient methods. That application will be the first merging of Brumbelow and Georgakakos methods with the more traditional reference ET irrigation scheduling model. Data sources for the assessment will include the National Climatic Data Center for historical meteorology, the Natural Resources Conservation Service for soils data, and the National Agricultural Statistics Service for historical crop yield data. The second part of this project will extend the CWPF-PD information described above into Probability Distributions of Net Profit-Water Functions (NPWF-PD s). These functions will input yield versus irrigation data into the full farm net profit calculus to include costs associated with irrigation as well as potential revenues from water sales. An example of this stochastic function is shown in Figure 3. The NPWF-PD can potentially be useful as a farm profitability planning tool and a as a means to assess the effectiveness of water resources management policies such as the EAA s 2-foot rule. The work contained in this project is intended to be part of a continuing research process. It is anticipated that the experience gained in this project will include understanding of modeling and optimization techniques, water resources planning processes, and manipulation and use of large climatic data sets. Extensions to this project will include real-time irrigation management tools and more extensive water resources policy assessment. The conflicts and policy difficulties of the Edwards Aquifer are likely the forerunner of ever more critical circumstances for water resources systems throughout Texas and the United States. The techniques developed in this project will no doubt find applicability in other water resources systems under extreme stress. 11. Results Expected from this Project (make this brief): It is expected that this project will produce preliminary assessments useful for water resources planning and management purposes and for farm profitability purposes for the Edwards Aquifer region of Texas. Moreover, the techniques developed and tested herein will be generally applicable to other system where agricultural use of water is important and part of a complex decision-making structure at multiple scales.

3 References Brumbelow, K. and A. Georgakakos. 2002a. Optimal single-site irrigation planning using physiologically based crop models. Agric. Systems. (in review). Brumbelow, K. and A. Georgakakos. 2002b. Consideration of temporal-climatic variability and change in agricultural water resources planning. Water Resour. Res. (in review). Tsuji, G.Y., G. Hoogenboom, and P.K. Thornton (eds.) Understanding Options for Agricultural Production. Kluwer Academic Publishers, Dordrecht, Netherlands.

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6 Ju Young Lee Curriculum Vitae Education Aug.2001~Present: Ph.D Course in division of Water Resource and Environmental Engineering, Department of Civil Engineering, College Station, Texas A & M University Sept.1998-Aug.2000 M.S(E)[Equivalent to an American M.S. degree] in division of Environmental System Engineering, Seoul, Korea University. (Supervisor Processor: Prof. Euiso Choi (Department of Civil Engr.) Mar.1993-Aug. 1998(Dual Major Program) B.S in Department of Food and Biotechnology, Seoul, Korea University B.S in Department of Civil Engineering, Seoul, Korea University Selected Publications Lee, JuYoung., Biodegradation of BTEX Contaminated Soil and Groundwater Using Microcosm Test, Master Thesis, Advisors: Dr. Euiso Choi, (echoi@korea.ac.kr),dr. Hyeung Kim (hyeong@korea), Korea University, Seoul, Korea, Choi E., Lee.J., Hwang H., Kwon S., Kang H., and Ko S(2000) Biological BTEX degration by Microbial Population in Petroleum Contaminated Soil, Journal of Korea Society of Environmental Engineering(KSEE), Session G-2, vol 2, pp 87-88, Seoul, Korea. Lee.J., Naufal Ziad, Carpio L, Amaya., and Donnelly, K.C(2002) PCB Pollution Control System of America Inc. in Bedford, OH, Research for Verification about EPA Region 5 (Chuyahoga Country/Bedford/OH 44146), Texas A&M University Awards Fellowship( ), Sam-Uk Construction and Engineering Co. Ltd.

7 KELLY BRUMBELOW Assistant Professor Environmental and Water Resources Engineering Division Department of Civil Engineering Texas A&M University College Station, TX EDUCATION: Ph.D. in Civil Engineering (2001), Georgia Institute of Technology B.S. Civil Engineering and B.S. International Affairs (1994), Georgia Institute of Technology PROFESSIONAL EXPERIENCE: Assistant Professor, Department of Civil Engineering, Texas A&M University ( Present) Research Engineer, School of Civil and Environmental Engineering; and Assistant Director, Georgia Water Resources Institute; Georgia Institute of Technology ( ) SELECTED HONORS AND AWARDS: UCOWR Dissertation Awards Honorable Mention (2002) ASCE Freeman Fellowship (1999) Georgia Tech School of CEE Outstanding Teaching Assistant Award (1996) NSF Graduate Research Fellowship ( ) SELECTED PUBLICATIONS: 1. Brumbelow, K. and A. Georgakakos An assessment of irrigation needs and crop yield for the United States under potential climate changes. Journal of Geophysical Research Atmospheres. 106(D21). 27,383-27, Brumbelow, K. and A. Georgakakos Optimal single-site irrigation planning using physiologically based crop models. Agricultural Systems. (in review). 3. Brumbelow, K. and A. Georgakakos Assessment of agricultural water resources sharing scenarios under objectives of efficiency, equity, and security. Water Resources Research. (in review). 4. Brumbelow, K. and A. Georgakakos Consideration of temporal-climatic variability and change in agricultural water resources planning. Water Resources Research. (in review).