GSA Position Statement:
Water Resources: Quantity

Adopted October 2021.

Conclusions and Recommendations

Mitigating present‐day and future, anticipated water shortages and managing water resources for the coming decades requires broad, sustained efforts and active collaboration among geoscientists, engineers, water-resource managers, planners, policy makers, and industry, who should seek to

• Improve the fundamental understanding of the quality, quantity, distribution, and use of water resources to increase the reliability and use of water‐resource management tools. Critical to this is an increased understanding of (1) the interactions between geological, biological, and ecological systems and that quantity also refers to useable quality (water fit for human and ecological consumption); and (2) the impacts of climate change on the water cycle and water resource distribution, including the role of soil moisture in the hydrologic cycle, changes in type and duration of precipitation, and surface water–groundwater interaction.
• Increase public investment in data collection and access to improve the scientific understanding of water resources. A comprehensive understanding can be achieved by maintaining current hydrologic data and monitoring capabilities; developing new data sets and ground- and space-based collection capabilities at the spatial and temporal resolution needed to support model analyses and decision making from local to regional scales; organizing data collection and management by surface‐water and groundwater hydrologic basins; and facilitating open access to these data sets.
• Support computational, risk‐based analyses to optimize data acquisition and enhance the scientific and socioeconomic basis of decision making for water resources management.
• Identify viable twenty-first–century approaches and alternatives when developing regulations, laws, compacts, or treaties involving the allocation and use of water resources. An understanding of the natural behavior, distribution, and variability of surface-water and groundwater is fundamental to the development of these approaches.

Rationale

Surface-water and groundwater resources are inextricably linked; changes in one impact the other. Climate change exacerbates these impacts by directly affecting the hydrologic cycle on local to global scales. Increases in temperature accelerate evaporation from open water, soils, and vegetation. Additional water in the atmosphere combined with heat fuel extreme weather events, change water distribution patterns, intensify precipitation, decrease snowpack, and alter the timing of peak snowmelt. Temperatures in the U.S. increased by 0.7 °C for the period 1986–2016 relative to 1901–1960, with the largest increases seen in Alaska and the western U.S., and projected late-century increases are even greater^1,2. Water distribution patterns will change as climate changes, resulting in too much water in some locations and too little water in others. A changing climate coupled with mis- or un-informed policy decisions further aggravate the problem.

Specifically, climate change will increase the frequency, intensity, and duration of drought in the western U.S., particularly the Southwest, with adverse impacts to water resources¹. The Colorado River Basin and other major river basins in the western U.S. are undergoing aridification, or the ongoing, permanent transformation to a drier environment, to varying degrees³. Impacts of droughts include reduced surface-water flow and groundwater storage, reduced agricultural productivity, loss of biodiversity, soil degradation and loss, wildfires, increases in invasive species and disease, and increases in heat-related human deaths⁴. Droughts are the second costliest weather- and climate-related disaster in the U.S. Between 1980 and 2021, 29 drought episodes resulted in at least US$1 billion in total damages for each event, with an average loss of $9.7 billion per event⁵.

Climate change will also lead to an increase in the frequency and intensity of heavy rainfall events (>99th percentile of daily values), most notably in the Midwest and in the Northeast, where changes average as much as 42% and 55% (compared to data available from 1958)¹. Additional increases exceeding 40% are projected by the end of the century (relative to 1986–2015)¹. Heavy rainfall events lead to increased runoff, flash flooding, mudflows and landslides, and sediment erosion and loading into the nation’s waterways, all with associated impacts to infrastructure (levees, dams, stormwater management systems, etc.) or agriculture. Long periods of heavy rainfall can also reduce the capacity of the soil and underlying geologic substrate to absorb water, thereby challenging the recovery and replenishment opportunities in aquifers. In addition to the challenges offered by flooding events (see the GSA Position Statement: U.S. Flood Risk Management), significant changes in the timing and volume of precipitation can lead to agricultural drought conditions (as opposed to meteorological drought), where peak water availability may be out of phase with the growing season⁶.

Thermoelectric power, irrigation, and public supply account for 90% of all surface-water and groundwater withdrawals in the U.S. (41%, 37%, and 12%, respectively)⁷. Although many renewable energy sources such as solar and wind reduce or eliminate the need for water in electricity production, reservoir hydropower and biofuel sources may have a large water footprint⁸. In addition, water is crucial for mining and processing minerals used in the manufacture of green technologies⁹.

Given the longer residence time of groundwater (compared to surface water), aquifers can be slow to respond to stresses, and problems may not be noticed and remedied for many years¹⁰. About 70% of groundwater withdrawals in the U.S. are used for agriculture, and the extraction rate increasingly exceeds the replenishment rate in many areas, resulting in decreased groundwater storage⁷. Total groundwater depletion in the U.S. from 1900–2008 was about 1000 km³, with faster depletion rates during 2000–200810. Two-thirds of the depletion is from the High Plains aquifer (the largest in the U.S.), the Gulf Coastal Plain aquifer system (Mississippi Embayment section), and the Central Valley aquifer in California^10,11. Sustained groundwater withdrawals and subsequent lowering of the water table can result in the loss of connectivity with and decreased flow of surface water. Streamflow losses can extend far beyond the region of pumping¹². Drilling deeper is not a sustainable solution; deeper aquifers tend to be more saline and require treatment, and deeper wells tend to have higher construction costs and energy demands¹³. Furthermore, deeper aquifers may contain fossil groundwater, where recharge could take thousands of years.

Mitigating groundwater depletion will require reducing demand, particularly in irrigated agriculture, and increasing supply through artificial aquifer recharge and other methods¹⁰. Efforts at the municipal level to capture stormwater and use gray water can enhance local water supplies and show promise for sustainable urban water management¹⁴. Any mitigation strategy is complicated by the fact that local groundwater conditions can be highly variable and cross geopolitical boundaries. Scientific and technical issues are often coupled with political, legal, and socioeconomic considerations and constraints¹⁰. Given these complexities, we must recognize that one technical approach is not appropriate for all aquifers, and solutions will require comprehensive and integrated analysis and discussion.

Comprehensive and robust data sets with high spatial and temporal resolution, including basin- and aquifer-scale geophysical data and three-dimensional geologic maps are needed to inform groundwater modeling and address the issues outlined above. The U.S. Geological Survey (USGS) has developed and maintained extensive surface- and groundwater monitoring networks¹⁵ and databases such as the National Hydrography Dataset¹⁶, but gaps in coverage and data remain¹⁷; the USGS is currently developing a Next Generation Water Observing System (NGWOS) that will address these gaps and eventually “provide high temporal and spatial resolution data on streamflow, evapotranspiration, snowpack, soil moisture, water quality, groundwater/surface-water connections, stream velocity distribution, sediment transport, and water use.”¹⁷ At regional and global scales, satellites such as the Gravity Recovery and Climate Experiment (GRACE) launched in 2002 and GRACE Follow-On (GRACE-FO) launched in 2018 provide terrestrial water storage information based on changes in Earth’s gravitational field¹⁸. Such data combined with ground- and model-based approaches are critical for understanding causes and variations in surface- and groundwater quantities, seasonal to decadal variations, and opportunities for storage and replenishment in the face of climate change, drought, flooding and runoff, and anthropogenic influence.

Opportunities for GSA and GSA Members to Help Implement Recommendations

To facilitate implementation of the goals of this position statement, The Geological Society of America recommends that its members take the following actions:

• Engage with policy makers to support efforts to mitigate present-day and future anticipated water shortages.
• Contact stakeholders (water managers, land managers, water users, policy makers, and regulators) to identify information and research needs and collaborate on the development of sustainable water‐resource management goals and plans.
• Participate in public-education activities to foster partnership and collaboration among local, state, and federal governments; educational and research institutions; energy, industrial, and agricultural users; and the public.
• Participate in professional forums to educate peers and the public about regional water quantity issues, including the role of climate change in altering the hydrologic cycle, and identify ways that better data and analyses can improve water‐resource management.
• Ensure that water footprint^19,20 (both direct and indirect water use) informs both personal and professional decisions every day as well during future planning efforts.
• Improve communication with decision makers and the public about water resource availability issues. Communication is aided by analogies and examples relevant to the affected stakeholders/populations.

References

1. USGCRP, 2018, Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II. Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart, eds., U.S. Global Change Research Program, Washington, D.C., USA, 1515 p., https://doi.org/10.7930/NCA4.
2. Vose, R.S., D.R. Easterling, K.E. Kunkel, A.N. LeGrande, and Wehner, M.F., 2017, Temperature Changes in the United States. Climate Science Special Report: Fourth National Climate Assessment, Volume I. Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock, eds., U.S. Global Change Research Program, Washington, D.C., USA, p. 185–206, https://doi.org/10.7930/J0N29V45.
3. Colorado River Research Group, 2018, When is drought not a drought? Drought, aridification, and the “new normal,” 4 p., https://www.coloradoriverresearchgroup.org/uploads/4/2/3/6/42362959/crrg_aridity_report.pdf.
4. National Drought Mitigation Center, 2020, Are you impacted by drought?, https://drought.unl.edu/ranchplan/DroughtBasics/AreYouImpactedbyDrought.aspx.
5. NOAA National Centers for Environmental Information (NCEI), 2020, U.S. Billion-Dollar Weather and Climate Disasters, https://www.ncdc.noaa.gov/billions/.
6. National Drought Mitigation Center, 2020, Types of drought, https://drought.unl.edu/Education/DroughtIn-depth/TypesofDrought.aspx.
7. Dieter, C.A., Maupin, M.A., Caldwell, R.R., Harris, M.A., Ivahnenko, T.I., Lovelace, J.K., Barber, N.L., and Linsey, K.S., 2018, Estimated use of water in the United States in 2015: U.S. Geological Survey Circular 1441, 65 p., https://doi.org/10.3133/cir1441. [Supersedes USGS Open-File Report 2017-1131.]
8. Jin, y., P. Behrens, A. Tukker, and L. Scherer, 2019, Water use of electricity technologies: A global meta-analysis, Renewable and Sustainable Energy Reviews, 115, https://doi.org/10.1016/j.rser.2019.109391.
9. Mudd, G.M., 2008. Sustainability reporting and water resources: a preliminary assessment of embodied water and sustainable mining, Mine Water and the Environment, 27, p. 136–144, https://doi.org/10.1007/s10230-008-0037-5.
10. Konikow, L.F., 2015, Long-Term Groundwater Depletion in the United States, Groundwater, v. 53, p. 2–9.
11. Council for Agricultural Science and Technology, 2019, Aquifer Depletion and Potential Impacts on Long-term Irrigated Agricultural Productivity, Issue Paper 63, 20 p., https://www.cast-science.org/publication/aquifer-depletion-and-potential-impacts-on-long-term-irrigated-agricultural-productivity/.
12. Condon, L.E. and Maxwell, R.M., 2019, Simulating the sensitivity of evapotranspiration and streamflow to large-scale groundwater depletion, Science Advances, v.5(6), 9 p., https://doi.org/doi:10.3390/rs10060829.
13. Perrone, D., and Jasechko, S., 2019, Deeper well drilling an unsustainable stopgap to groundwater depletion. Nature Sustainability, v. 2, p. 773–782 https://doi.org/10.1038/s41893-019-0325-z.
14. National Academies of Sciences, Engineering, and Medicine, 2016, Using Graywater and Stormwater to Enhance Local Water Supplies: An Assessment of Risks, Costs, and Benefits. Washington, D.C.: The National Academies Press, https://doi.org/10.17226/21866.
15. U.S. Geological Survey, 2021, Water Resources, https://www.usgs.gov/mission-areas/water-resources/data-tools.
16. U.S. Geological Survey, 2021, National Hydrography, https://www.usgs.gov/core-science-systems/ngp/national-hydrography/.
17. U.S. Geological Survey, 2021, Next Generation Water Observing System, https://www.usgs.gov/mission-areas/water-resources/science/usgs-next-generation-water-observing-system-ngwos?qt-science_center_objects=0#qt-science_center_objects.
18. Frappart, F., and Ramillien, G., 2018, Monitoring Groundwater Storage Changes Using the Gravity Recovery and Climate Experiment (GRACE) Satellite Mission: A Review, Remote Sensing, v.10, p. 829, https://www.mdpi.com/2072-4292/10/6/829.
19. Hoekstra, A. & Hung, P., 2002, Virtual Water Trade: A Quantification of Virtual Water Flows between Nations in Relation to International Crop Trade Value of Water Research Report Series No. 11 (UNESCO-IHE Institute for Water Education), http://www.waterfootprint.org/Reports/Report11.pdf.
20. Hoekstra, A.Y. & Mekonnen, M.M., 2012, The water footprint of humanity. Proc. Natl Acad. Sci. USA, v. 109(9), p. 3232–3237, https://doi.org/10.1073/pnas.1109936109.