Science Center Objects

The Issue: Fresh groundwater withdrawals for irrigation from 66 principal aquifers in the United States comprised approximately three-fourths of total groundwater withdrawals in the year 2000. The magnitude of these withdrawals is certainly substantial but difficult to quantify because few states actually monitor groundwater withdrawals for irrigation. Water-resource managers are also interested in how much of a withdrawal is lost to consumptive use (primarily evapotranspiration) and how much ends up as return flow (not used consumptively and thus available for further use.) The magnitude of the consumptive use of groundwater withdrawals for irrigation is, again, substantial but difficult to quantify, and no states monitor consumptive use of the withdrawals.

How USGS will help: By leveraging ongoing groundwater resource assessments in principal aquifers of the U.S., the USGS will develop and demonstrate remote-sensing based methods to consistently estimate consumptive use of irrigation water on national and regional scales.

9722-E57 - Consumptive Water Use and Groundwater Withdrawals in Irrigated Lands - Completed FY2014

Problem - There is a need to develop and test a consistent, accurate, and efficient approach for estimating groundwater withdrawn for irrigation and the associated consumptive use of the withdrawals on a regional scale. Recent advances in remote-sensing technology and energy-balance methods now allow more accurate and repeatable direct estimates of actual evapotranspiration (ETa) from irrigated lands, the predominant component of consumptive use. The required remote-sensing imagery is available from 1979 to present for the entire continental U.S. We thus have an opportunity to develop historical geospatial datasets of consumptive use for irrigated lands throughout the Nation, and to further use those datasets to estimate groundwater withdrawals for irrigation on a scale that is consistent with the principal aquifers of the Nation. Further development of these methods will support an operational system for updating nationwide estimates of irrigation water use, and for improving groundwater withdrawal and consumptive use estimates for basin-, regional-, and national-scale water availability assessments.

Objectives - The objectives of this study are to develop and demonstrate remote-sensing-based methods to consistently estimate consumptive use of irrigation water on national and regional scales. On a national scale, our objective is to demonstrate the utility of these methods for improving the accuracy and consistency of estimates of consumptive use (ETa) of irrigation water, and to then explore geographic and recent (1990-2005) temporal trends in the data. On a regional scale, we will further develop methods to incorporate remotely-sensed ETa data into water-budget models to derive more accurate and consistent estimates of groundwater withdrawals and consumptive use for different hydro-climatic regions in the U.S., and for selected principal aquifer systems including the Columbia Plateau and High Plains.

Relevance and Benefits - This study is consistent with the national USGS mission and goals identified in the USGS Science Strategy document. The study will help develop a clear knowledge of the status of the Nation’s water resources, data on trends in water availability and use over recent decades, and an improved ability to forecast the availability of freshwater for future human, economic, and environmental uses.

Approach - The study includes national- and regional-scale approaches that build on recent efforts to estimate monthly, seasonal, and annual ETa using energy-balance methods with remotely-sensed thermal imagery collected by Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Very High Resolution Radiometer (AVHRR) sensors. At the national scale, monthly ETa will be estimated and provided at two spatial scales at 5-year increments from at least 1990 through 2005. Selected consumptive use estimates made using this approach will be compared to measured irrigation withdrawals where possible, and to consumptive use estimates reported in pre-1995 USGS water use compilations. At the regional scale, we will explore improvements to an existing method that uses remotely-sensed ETa estimates combined with a water balance model to estimate irrigation demand and groundwater withdrawals. The potential improvements include downscaling the current ETa estimates to a 100-m resolution, methods to differentiate surface-water and groundwater irrigation withdrawals, and more accurate methods to determine the fraction of estimated ETa supplied by precipitation.