Groundwater depletion and irrigated agriculture in the semi-arid grasslands of the central USA

January 28th, 2014

Prof. David R. Steward, Kansas State University, United States

Groundwater currently provides a reliable source of water for irrigation in the central plains of the USA. Trade-offs exist in many areas where the shorter-term gains from water-use in irrigated agriculture is leading to groundwater depletion, and must be balanced with the longer-term needs. Recent research by the author, who is a professor at a land-grant university, builds towards understanding groundwater and its connectivity with social and natural processes.

Hydrology

Groundwater flow in the Ogallala/High Plains Aquifer of the central plains (see Figure 1) is driven by a gently sloping base1 with a west-east gradient of approximately 1/500. Groundwater seeps down-gradient until it eventually reemerges to the land surface. The water may reemerge as baseflow that sustains rivers during dry periods, as uptake by phreatophyte plants that directly tap groundwater, or as pumping from wells.

Regional water balances have been quantified near the Konza Prairie Long-Term Ecological Research site by Steward et al. (2011).2 Such studies are founded on a mathematical technique called the Analytic Element Method3, which enables the development of accurate solutions for modeling groundwater interaction with rivers.4 These models provide a basis for developing simpler hydrologic response functions5, which can be used to study changes in the groundwater table both up- and down-gradient from the point of water use. Studies by the author are facilitated by integrating the vector-based Analytic Element Method with GIScience methods6 and raster data for spatial analysis of results.7

Anthropogenic forcings and interdisciplinary modeling

The models and data methods used to study groundwater flow in the central plains have been integrated with agricultural economic models by Steward et al. (2009).8 Such studies provide a clearer understanding of the relationship between groundwater use, economic activity, and the impacts of policy change. These methods have also been integrated with agricultural models of crop production in Bulatewicz et al. (2009)9 to study the interactions between groundwater, economics, and crop production. Models are linked using the OpenMI (Open Modelling Interface), which has emerged from the EU Water Framework Directive as a standardized method to pass variables between models. Such paradigms enable groundwater model inputs and outputs to be utilized by models of other processes, and facilitate systemic understanding of water resources systems.

Our use of this technique in Bulatewicz et al. (2010)10 passes crop choice from the economic model to the agriculture model, which passes irrigation water needs to the groundwater model. This in turn passes available stores for the next year to the economic model, which uses this information to modify the possible crop choices based upon water availability. The key to the implementation of our integrated models was development of Simple Script Wrappers (SSW), which allows code written in Matlab, Scilab, or Python to be easily integrated into an OpenMI model.11

Ecohydrologic ramifications

The source of groundwater recharge is that portion of precipitation that does not run-off the land, evaporate, or transpire through plants. A portion of groundwater is brought up by phreatophytes, which are trees that exist primarily in riverbeds of the region, and are capable of directly tapping groundwater. A mathematical and computer model of this uptake was developed in Steward and Ahring (2009)12 to study the source of water captured by phreatophytes. This model showed that fields of trees are capable of extracting water from considerable depths. The distribution of phreatophytes was studied in Ahring and Steward (2012)13 to assess the relationship between areas of tree extirpation and lowering of the groundwater table. These results show promise for using observed changes in phyreatophyte distribution to identify areas with groundwater depletion.

Vulnerability and resiliency

A hyper-extractive system exists in the central plains of the USA, where irrigated agriculture provides the basis of a vibrant agricultural economy.14 Groundwater stores provide the resiliency for the region to sustain itself through dry weather periods. However, the depletion of groundwater that supports this region is creating long-term sustainability challenges. There is a clear need for science and engineering to study this region and to provide the support needed to inform the decision making process. An integrated study by Steward et al. (2013) develops methods to provide groundwater projections which are integrated with crop production for the livestock sector, and projects the outcomes of changes in groundwater levels on current and future crop production. The approach allows an understanding of the consequences of changes in groundwater resources and the impact of proactively reducing water-use now for future generations.

The role of the land-grant universities

The Morrill Act of 1862 established a system of state land-grant universities in the USA with a mission of research, education, outreach and service, targeting regional issues. The problems facing society in balancing water needs today and in the future require a broader understanding of the consequences of change.15 The land-grant universities provide a perspective of interdisciplinary knowledge and understanding, and they are uniquely positioned to provide the regional engineering and scientific support necessary for informed decision making.

References:

1. Steward, D. R., Groundwater response to changing water-use practices in sloping aquifers, Water Resources Research, 43, W05408, doi:10.1029/2005WR004837, 2007. http://dx.doi.org/10.1029/2005WR004837

2. Steward, D. R., Yang, X., Lauwo, S. Y., Staggenborg, S. A., Macpherson, G. L. and Welch, S. M., From precipitation to groundwater baseflow in a native prairie ecosystem: a regional study of the Konza LTER in the Flint Hills of Kansas, USA, Hydrology and Earth System Sciences, 15, 3181-3194, 2011. http://dx.doi.org/10.5194/hess-15-3181-2011

3. Steward, D. R. and A. J. Allen, The Analytic Element Method for rectangular gridded domains and application to the Ogallala Aquifer, Advances in Water Resources, 60, 89-99, 2013. http://dx.doi.org/10.1016/j.advwatres.2013.07.009

4. Steward, D. R., Le Grand, P., Jankovic, I. and Strack, O.D.L., Analytic formulation of Cauchy integrals for boundary segments with curvilinear geometry, Proceedings of The Royal Society of London, Series A, 464, 223-248, 2008. http://dx.doi.org/10.1098/rspa.2007.0138

5. Steward, D. R., Yang, X., and Chacon, S., Groundwater response to changing water-use practices in sloping aquifers using convolution of transient response functions, Water Resources Research, 45, W02412:1-13, 2009b. http://dx.doi.org/10.1029/2007WR006775

6. Steward, D. R. and Bernard, E. A., The synergistic powers of AEM and GIS geodatabase models in water resources studies, Ground Water, 44(1), 56-61, 2006. http://dx.doi.org/10.1111/j.1745-6584.2005.00172.x

7. Yang, X., Steward, D. R., de Lange, W. J., Lauwo, S. Y., Chubb, R. M. and Bernard, E. A., Data model for system conceptualization in groundwater studies, International Journal of GIS, 24(5), 677-694, 2010. http://dx.doi.org/10.1080/13658810902967389

8. Steward, D. R., Peterson, J. M., Yang, X., Bulatewicz, T., Herrera, M., Mao, D. and Hendricks, N., Groundwater economics: An object oriented foundation for integrated studies of irrigated agricultural systems, Water Resources Research, 45, W05430:1-15, 2009a.

9. Bulatewicz, T., Jin, W., Staggenborg, S., Lauwo, S. Y., Miller, M., Das, S., Andresen, D., Peterson, J., Steward, D. R., and Welch, S. M., Calibration of a crop model to irrigated water use using a genetic algorithm, Hydrology and Earth System Sciences, 13, 1467-1483, 2009. http://dx.doi.org/10.5194/hess-13-1467-2009

10. Bulatewicz, T., Yang, X., Peterson, J. M., Staggenborg, S., Welch, S. M., and D. R. Steward, Accessible integration of agriculture, groundwater, and economic models using the Open Modeling Interface (OpenMI): Methodology and initial results, Hydrology and Earth System Sciences, 14, 521-534, 2010. http://dx.doi.org/10.5194/hess-14-521-2010

11. Bulatewicz, T., A. Allen, J.M. Peterson, S. Staggenborg, S.M. Welch, and D.R. Steward, The Simple Script Wrapper for OpenMI: Enabling interdisciplinary modeling studies, Environmental Modelling & Software, 39, 283-294, 2013. http://dx.doi.org/10.1016/j.envsoft.2012.07.006

12. Steward, D. R. and Ahring, T., An analytic solution for groundwater uptake by phreatophytes spanning spatial scales from plant to field to regional, Journal of Engineering Mathematics, 64(2), 85-103, 2009. http://dx.doi.org/10.1007/s10665-008-9255-x

13. Ahring, T. S. and D. R. Steward, Groundwater surface water interactions and the role of phreatophytes in identifying recharge zones, Hydrology and Earth System Sciences, 16, 4133-4142, 2012. http://dx.doi.org/10.5194/hess-16-4133-2012

14. Aistrup, J. A., Kulcsar, L., Beach, S., Mauslein, J. and D. R. Steward, Hyper-extractive economies in the U.S.: A coupled-systems approach, Applied Geography, 37, 88-100, 2013. http://dx.doi.org/10.1016/j.apgeog.2012.09.010

15. Steward, D. R., Bruss, P. J., Yang, X., Staggenborg, S. A., Welch, S. M. and M. D. Apley, Tapping unsustainable groundwater stores for agricultural production in the High Plains Aquifer of Kansas, projections to 2110, Proceedings of the National Academy of Sciences of the United States of America, 110(37) E3477-E3486, September 10, 2013. http://dx.doi.org/10.1073/pnas.1220351110

David R. Steward is a professor in Civil Engineering at Kansas State University, a land-grant university. Prof. Steward’s research interests include: interdisciplinary water resources modeling, groundwater flow, the Analytic Element Method, mathematical and computational methods in boundary value problems, and providing engineering support for society to address water resources sustainability challenges.

The views expressed in this article belong to the individual authors and do not represent the views of the Global Water Forum, the UNESCO Chair in Water Economics and Transboundary Water Governance, UNESCO, the Australian National University, or any of the institutions to which the authors are associated. Please see the Global Water Forum terms and conditions here.