— January 11, 2018
In New Mexico, groundwater accounts for approximately 50% of total water use and 75% of public water supplies. Over the last several years, groundwater levels in many areas of the state have been declining due to a combination of drought and groundwater pumping. Groundwater is replenished by a process called recharge, where snowmelt and rain infiltrates through the soil and slowly moves through the subsurface to eventually reach an aquifer. Because groundwater recharge defines a limit for the availability of groundwater, estimating recharge for the state of New Mexico is necessary for effective water resource management. However, quantification of groundwater recharge represents a significant gap in current understanding of the New Mexico water budget.
The New Mexico Statewide Water Assessment (SWA), which is funded by the New Mexico State Legislature through the New Mexico Water Resources Research Institute (WRRI), is a collaborative effort between state and federal agencies, New Mexico universities, and private consultants, to provide new, dynamic, spatially representative assessments of water budgets for the entire state of New Mexico. As part of the SWA, NMBGMR hydrogeologist, Talon Newton has been working with NMT faculty members and graduate students to develop a model that estimates groundwater recharge for the entire state. The EvapoTranspiration and Recharge Model (ETRM) uses readily available spatial datasets that provide information about climate (e.g. precipitation, net solar radiation, and/or temperature), topography, soil characteristics, geology, and vegetation cover to assess what happens to rain and snow that falls in New Mexico. Using estimated values of daily precipitation as the total input of water, the ETRM calculates how much of this water runs off into streams, infiltrates into the subsurface, is stored in the soil, evaporates and is used by vegetation. Any water that is left over is counted as recharge. This series of calculations has been done for everyday over a 14 year simulation period (2000 – 2013) in over 5 million 250m x 250m cells that uniformly cover the state. Results are preliminary as researchers and students are currently working to improve the accuracy of recharge estimates. Possible applications of this model include the improvement of current hydrologic models being used for water resource management, use in state and regional water planning, and forecasting future changes in recharge due to land use change and climate change.