Estimating Groundwater Withdrawals and Consumptive Use for Principal Aquifers

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The USGS works in cooperation with local, State, and Federal agencies to compile and disseminate data on the Nation's water use. The annual water-use estimates are reported at the county, State, and national levels and provide fundamental input to regional hydrologic models. These estimates commonly represent the largest stresses in most aquifers and are needed by local managers to steward the resources and to support regional simulation of the resources to quantify the effects of this water use. 

Map of California showing locations where hydrologic models using MODFLOW

Selected locations where hydrologic models using MODFLOW with the Farm Process are available for consumptive-use and groundwater withdrawal comparisons.

(Public domain.)

Estimated groundwater withdrawals and consumptive use are commonly indirectly based on power records, land use, and census data. These methods have particular difficulties and often yield poor resolution spatial distributions of groundwater withdrawals or consumptive use that cannot be readily distributed for regional simulation with a hydrologic model. In addition, there is a need for monthly estimates of water use in many areas to help water managers have an accurate estimate of the supply and demand components of the hydrologic budget. 

The objectives of this study would be to develop tools and assess the utility of incorporating remotely-sensed information such as land use and actual ET data (ETact) to support the application of hydrologic models of regional aquifer systems where agricultural water use is significant.

The proposed study would compare remotely sensed, land-use based, metered, and simulated estimates of pumpage. This approach would help delineate how modeling and remote-sensing techniques can augment, supplement, or be used in place of metered pumpage, which is still lacking in most regions.The analysis can be performed at different scales to see how accounting at these scales affects the accuracy and uncertainty of water use. Estimations of land use and local climate over selected periods will be used to further refine the water-use estimation techniques and assess the combined effects of uncertainty in climatic and land-use components of water use. The uncertainty of these estimates could be analyzed with respect to several areas where recent hydrologic models have been completed with MF-FMP. The approach would be twofold: (1) an assessment of consumptive use would be performed for selected models where MF-FMP has been applied at different scales; and (2) tools will be developed to use the remotely sensed changes in land use, changes in crops, changes in fractions of land available for transpiration and evaporation as MF-FMP model input data and observations for calibration of simulated consumptive use.